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1.14 |
=head1 LIBECB - e-C-Builtins |
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1.3 |
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1.14 |
=head2 ABOUT LIBECB |
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Libecb is currently a simple header file that doesn't require any |
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configuration to use or include in your project. |
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1.16 |
It's part of the e-suite of libraries, other members of which include |
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1.14 |
libev and libeio. |
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Its homepage can be found here: |
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http://software.schmorp.de/pkg/libecb |
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1.85 |
It mainly provides a number of wrappers around many compiler built-ins, |
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together with replacement functions for other compilers. In addition |
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to this, it provides a number of other lowlevel C utilities, such as |
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endianness detection, byte swapping or bit rotations. |
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Or in other words, things that should be built into any standard C |
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system, but aren't, implemented as efficient as possible with GCC (clang, |
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msvc...), and still correct with other compilers. |
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1.17 |
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1.14 |
More might come. |
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1.3 |
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=head2 ABOUT THE HEADER |
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At the moment, all you have to do is copy F<ecb.h> somewhere where your |
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compiler can find it and include it: |
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#include <ecb.h> |
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The header should work fine for both C and C++ compilation, and gives you |
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all of F<inttypes.h> in addition to the ECB symbols. |
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1.16 |
There are currently no object files to link to - future versions might |
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1.14 |
come with an (optional) object code library to link against, to reduce |
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code size or gain access to additional features. |
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It also currently includes everything from F<inttypes.h>. |
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=head2 ABOUT THIS MANUAL / CONVENTIONS |
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This manual mainly describes each (public) function available after |
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including the F<ecb.h> header. The header might define other symbols than |
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these, but these are not part of the public API, and not supported in any |
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way. |
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When the manual mentions a "function" then this could be defined either as |
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as inline function, a macro, or an external symbol. |
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When functions use a concrete standard type, such as C<int> or |
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C<uint32_t>, then the corresponding function works only with that type. If |
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only a generic name is used (C<expr>, C<cond>, C<value> and so on), then |
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the corresponding function relies on C to implement the correct types, and |
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is usually implemented as a macro. Specifically, a "bool" in this manual |
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refers to any kind of boolean value, not a specific type. |
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1.1 |
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1.40 |
=head2 TYPES / TYPE SUPPORT |
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ecb.h makes sure that the following types are defined (in the expected way): |
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int8_t uint8_ |
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int16_t uint16_t |
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int32_t uint32_ |
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int64_t uint64_t |
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int_fast8_t uint_fast8_t |
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int_fast16_t uint_fast16_t |
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int_fast32_t uint_fast32_t |
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int_fast64_t uint_fast64_t |
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intptr_t uintptr_t |
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1.40 |
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The macro C<ECB_PTRSIZE> is defined to the size of a pointer on this |
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1.45 |
platform (currently C<4> or C<8>) and can be used in preprocessor |
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expressions. |
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1.40 |
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1.74 |
For C<ptrdiff_t> and C<size_t> use C<stddef.h>/C<cstddef>. |
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1.49 |
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1.62 |
=head2 LANGUAGE/ENVIRONMENT/COMPILER VERSIONS |
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1.43 |
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1.46 |
All the following symbols expand to an expression that can be tested in |
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1.44 |
preprocessor instructions as well as treated as a boolean (use C<!!> to |
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ensure it's either C<0> or C<1> if you need that). |
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=over |
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=item ECB_C |
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True if the implementation defines the C<__STDC__> macro to a true value, |
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while not claiming to be C++, i..e C, but not C++. |
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=item ECB_C99 |
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True if the implementation claims to be compliant to C99 (ISO/IEC |
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9899:1999) or any later version, while not claiming to be C++. |
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1.47 |
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Note that later versions (ECB_C11) remove core features again (for |
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example, variable length arrays). |
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=item ECB_C11, ECB_C17 |
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True if the implementation claims to be compliant to C11/C17 (ISO/IEC |
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9899:2011, :20187) or any later version, while not claiming to be C++. |
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=item ECB_CPP |
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True if the implementation defines the C<__cplusplus__> macro to a true |
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value, which is typically true for C++ compilers. |
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1.74 |
=item ECB_CPP11, ECB_CPP14, ECB_CPP17 |
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1.44 |
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True if the implementation claims to be compliant to C++11/C++14/C++17 |
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(ISO/IEC 14882:2011, :2014, :2017) or any later version. |
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1.43 |
|
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1.83 |
Note that many C++20 features will likely have their own feature test |
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macros (see e.g. L<http://eel.is/c++draft/cpp.predefined#1.8>). |
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1.81 |
=item ECB_OPTIMIZE_SIZE |
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Is C<1> when the compiler optimizes for size, C<0> otherwise. This symbol |
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can also be defined before including F<ecb.h>, in which case it will be |
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unchanged. |
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1.57 |
=item ECB_GCC_VERSION (major, minor) |
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1.43 |
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1.84 |
Expands to a true value (suitable for testing by the preprocessor) if the |
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compiler used is GNU C and the version is the given version, or higher. |
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1.43 |
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This macro tries to return false on compilers that claim to be GCC |
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compatible but aren't. |
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1.50 |
=item ECB_EXTERN_C |
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Expands to C<extern "C"> in C++, and a simple C<extern> in C. |
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This can be used to declare a single external C function: |
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ECB_EXTERN_C int printf (const char *format, ...); |
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=item ECB_EXTERN_C_BEG / ECB_EXTERN_C_END |
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These two macros can be used to wrap multiple C<extern "C"> definitions - |
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they expand to nothing in C. |
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They are most useful in header files: |
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ECB_EXTERN_C_BEG |
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int mycfun1 (int x); |
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int mycfun2 (int x); |
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ECB_EXTERN_C_END |
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=item ECB_STDFP |
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1.84 |
If this evaluates to a true value (suitable for testing by the |
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1.50 |
preprocessor), then C<float> and C<double> use IEEE 754 single/binary32 |
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and double/binary64 representations internally I<and> the endianness of |
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both types match the endianness of C<uint32_t> and C<uint64_t>. |
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This means you can just copy the bits of a C<float> (or C<double>) to an |
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C<uint32_t> (or C<uint64_t>) and get the raw IEEE 754 bit representation |
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without having to think about format or endianness. |
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This is true for basically all modern platforms, although F<ecb.h> might |
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not be able to deduce this correctly everywhere and might err on the safe |
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side. |
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1.87 |
=item ECB_64BIT_NATIVE |
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Evaluates to a true value (suitable for both preprocessor and C code |
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testing) if 64 bit integer types on this architecture are evaluated |
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"natively", that is, with similar speeds as 32 bit integerss. While 64 bit |
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integer support is very common (and in fatc required by libecb), 32 bit |
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cpus have to emulate operations on them, so you might want to avoid them. |
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1.54 |
=item ECB_AMD64, ECB_AMD64_X32 |
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These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32 |
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ABI, respectively, and undefined elsewhere. |
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The designers of the new X32 ABI for some inexplicable reason decided to |
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make it look exactly like amd64, even though it's completely incompatible |
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to that ABI, breaking about every piece of software that assumed that |
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C<__x86_64> stands for, well, the x86-64 ABI, making these macros |
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necessary. |
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1.43 |
=back |
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1.62 |
=head2 MACRO TRICKERY |
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1.88 |
=over |
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1.62 |
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=item ECB_CONCAT (a, b) |
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Expands any macros in C<a> and C<b>, then concatenates the result to form |
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a single token. This is mainly useful to form identifiers from components, |
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e.g.: |
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#define S1 str |
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#define S2 cpy |
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ECB_CONCAT (S1, S2)(dst, src); // == strcpy (dst, src); |
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=item ECB_STRINGIFY (arg) |
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Expands any macros in C<arg> and returns the stringified version of |
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it. This is mainly useful to get the contents of a macro in string form, |
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e.g.: |
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#define SQL_LIMIT 100 |
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sql_exec ("select * from table limit " ECB_STRINGIFY (SQL_LIMIT)); |
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1.64 |
=item ECB_STRINGIFY_EXPR (expr) |
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Like C<ECB_STRINGIFY>, but additionally evaluates C<expr> to make sure it |
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is a valid expression. This is useful to catch typos or cases where the |
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macro isn't available: |
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#include <errno.h> |
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ECB_STRINGIFY (EDOM); // "33" (on my system at least) |
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ECB_STRINGIFY_EXPR (EDOM); // "33" |
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// now imagine we had a typo: |
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ECB_STRINGIFY (EDAM); // "EDAM" |
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ECB_STRINGIFY_EXPR (EDAM); // error: EDAM undefined |
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1.62 |
=back |
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sf-exg |
1.60 |
=head2 ATTRIBUTES |
233 |
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1.1 |
|
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sf-exg |
1.60 |
A major part of libecb deals with additional attributes that can be |
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assigned to functions, variables and sometimes even types - much like |
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C<const> or C<volatile> in C. They are implemented using either GCC |
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attributes or other compiler/language specific features. Attributes |
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declarations must be put before the whole declaration: |
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1.20 |
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ecb_const int mysqrt (int a); |
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ecb_unused int i; |
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1.88 |
=over |
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1.1 |
|
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1.3 |
=item ecb_unused |
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Marks a function or a variable as "unused", which simply suppresses a |
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1.85 |
warning by the compiler when it detects it as unused. This is useful when |
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you e.g. declare a variable but do not always use it: |
250 |
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1.3 |
|
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1.15 |
{ |
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sf-exg |
1.61 |
ecb_unused int var; |
253 |
root |
1.3 |
|
254 |
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1.15 |
#ifdef SOMECONDITION |
255 |
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var = ...; |
256 |
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return var; |
257 |
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#else |
258 |
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return 0; |
259 |
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#endif |
260 |
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} |
261 |
root |
1.3 |
|
262 |
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1.56 |
=item ecb_deprecated |
263 |
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264 |
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Similar to C<ecb_unused>, but marks a function, variable or type as |
265 |
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deprecated. This makes some compilers warn when the type is used. |
266 |
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267 |
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1.62 |
=item ecb_deprecated_message (message) |
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269 |
root |
1.67 |
Same as C<ecb_deprecated>, but if possible, the specified diagnostic is |
270 |
root |
1.62 |
used instead of a generic depreciation message when the object is being |
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used. |
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273 |
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1.31 |
=item ecb_inline |
274 |
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1.29 |
|
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1.73 |
Expands either to (a compiler-specific equivalent of) C<static inline> or |
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to just C<static>, if inline isn't supported. It should be used to declare |
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functions that should be inlined, for code size or speed reasons. |
278 |
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1.29 |
|
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Example: inline this function, it surely will reduce codesize. |
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1.31 |
ecb_inline int |
282 |
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1.29 |
negmul (int a, int b) |
283 |
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{ |
284 |
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return - (a * b); |
285 |
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} |
286 |
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287 |
root |
1.2 |
=item ecb_noinline |
288 |
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|
289 |
sf-exg |
1.66 |
Prevents a function from being inlined - it might be optimised away, but |
290 |
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1.3 |
not inlined into other functions. This is useful if you know your function |
291 |
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is rarely called and large enough for inlining not to be helpful. |
292 |
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293 |
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1.2 |
=item ecb_noreturn |
294 |
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295 |
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1.17 |
Marks a function as "not returning, ever". Some typical functions that |
296 |
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don't return are C<exit> or C<abort> (which really works hard to not |
297 |
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return), and now you can make your own: |
298 |
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299 |
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ecb_noreturn void |
300 |
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my_abort (const char *errline) |
301 |
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{ |
302 |
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puts (errline); |
303 |
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abort (); |
304 |
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} |
305 |
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|
306 |
sf-exg |
1.19 |
In this case, the compiler would probably be smart enough to deduce it on |
307 |
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its own, so this is mainly useful for declarations. |
308 |
root |
1.17 |
|
309 |
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1.53 |
=item ecb_restrict |
310 |
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311 |
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Expands to the C<restrict> keyword or equivalent on compilers that support |
312 |
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them, and to nothing on others. Must be specified on a pointer type or |
313 |
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an array index to indicate that the memory doesn't alias with any other |
314 |
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restricted pointer in the same scope. |
315 |
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316 |
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Example: multiply a vector, and allow the compiler to parallelise the |
317 |
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loop, because it knows it doesn't overwrite input values. |
318 |
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319 |
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void |
320 |
sf-exg |
1.61 |
multiply (ecb_restrict float *src, |
321 |
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ecb_restrict float *dst, |
322 |
root |
1.53 |
int len, float factor) |
323 |
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{ |
324 |
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int i; |
325 |
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326 |
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for (i = 0; i < len; ++i) |
327 |
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dst [i] = src [i] * factor; |
328 |
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} |
329 |
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330 |
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1.2 |
=item ecb_const |
331 |
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|
332 |
sf-exg |
1.19 |
Declares that the function only depends on the values of its arguments, |
333 |
root |
1.17 |
much like a mathematical function. It specifically does not read or write |
334 |
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any memory any arguments might point to, global variables, or call any |
335 |
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non-const functions. It also must not have any side effects. |
336 |
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337 |
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Such a function can be optimised much more aggressively by the compiler - |
338 |
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for example, multiple calls with the same arguments can be optimised into |
339 |
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a single call, which wouldn't be possible if the compiler would have to |
340 |
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expect any side effects. |
341 |
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342 |
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It is best suited for functions in the sense of mathematical functions, |
343 |
sf-exg |
1.19 |
such as a function returning the square root of its input argument. |
344 |
root |
1.17 |
|
345 |
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Not suited would be a function that calculates the hash of some memory |
346 |
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area you pass in, prints some messages or looks at a global variable to |
347 |
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decide on rounding. |
348 |
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|
349 |
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See C<ecb_pure> for a slightly less restrictive class of functions. |
350 |
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|
351 |
root |
1.2 |
=item ecb_pure |
352 |
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|
353 |
root |
1.17 |
Similar to C<ecb_const>, declares a function that has no side |
354 |
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effects. Unlike C<ecb_const>, the function is allowed to examine global |
355 |
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variables and any other memory areas (such as the ones passed to it via |
356 |
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pointers). |
357 |
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358 |
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While these functions cannot be optimised as aggressively as C<ecb_const> |
359 |
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functions, they can still be optimised away in many occasions, and the |
360 |
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compiler has more freedom in moving calls to them around. |
361 |
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362 |
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Typical examples for such functions would be C<strlen> or C<memcmp>. A |
363 |
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function that calculates the MD5 sum of some input and updates some MD5 |
364 |
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state passed as argument would I<NOT> be pure, however, as it would modify |
365 |
|
|
some memory area that is not the return value. |
366 |
|
|
|
367 |
root |
1.2 |
=item ecb_hot |
368 |
|
|
|
369 |
root |
1.17 |
This declares a function as "hot" with regards to the cache - the function |
370 |
|
|
is used so often, that it is very beneficial to keep it in the cache if |
371 |
|
|
possible. |
372 |
|
|
|
373 |
|
|
The compiler reacts by trying to place hot functions near to each other in |
374 |
|
|
memory. |
375 |
|
|
|
376 |
sf-exg |
1.19 |
Whether a function is hot or not often depends on the whole program, |
377 |
root |
1.17 |
and less on the function itself. C<ecb_cold> is likely more useful in |
378 |
|
|
practise. |
379 |
|
|
|
380 |
root |
1.2 |
=item ecb_cold |
381 |
|
|
|
382 |
root |
1.17 |
The opposite of C<ecb_hot> - declares a function as "cold" with regards to |
383 |
|
|
the cache, or in other words, this function is not called often, or not at |
384 |
|
|
speed-critical times, and keeping it in the cache might be a waste of said |
385 |
|
|
cache. |
386 |
|
|
|
387 |
|
|
In addition to placing cold functions together (or at least away from hot |
388 |
|
|
functions), this knowledge can be used in other ways, for example, the |
389 |
|
|
function will be optimised for size, as opposed to speed, and codepaths |
390 |
|
|
leading to calls to those functions can automatically be marked as if |
391 |
root |
1.27 |
C<ecb_expect_false> had been used to reach them. |
392 |
root |
1.17 |
|
393 |
|
|
Good examples for such functions would be error reporting functions, or |
394 |
|
|
functions only called in exceptional or rare cases. |
395 |
|
|
|
396 |
root |
1.2 |
=item ecb_artificial |
397 |
|
|
|
398 |
root |
1.17 |
Declares the function as "artificial", in this case meaning that this |
399 |
root |
1.52 |
function is not really meant to be a function, but more like an accessor |
400 |
root |
1.17 |
- many methods in C++ classes are mere accessor functions, and having a |
401 |
|
|
crash reported in such a method, or single-stepping through them, is not |
402 |
|
|
usually so helpful, especially when it's inlined to just a few instructions. |
403 |
|
|
|
404 |
|
|
Marking them as artificial will instruct the debugger about just this, |
405 |
|
|
leading to happier debugging and thus happier lives. |
406 |
|
|
|
407 |
|
|
Example: in some kind of smart-pointer class, mark the pointer accessor as |
408 |
|
|
artificial, so that the whole class acts more like a pointer and less like |
409 |
|
|
some C++ abstraction monster. |
410 |
|
|
|
411 |
|
|
template<typename T> |
412 |
|
|
struct my_smart_ptr |
413 |
|
|
{ |
414 |
|
|
T *value; |
415 |
|
|
|
416 |
|
|
ecb_artificial |
417 |
|
|
operator T *() |
418 |
|
|
{ |
419 |
|
|
return value; |
420 |
|
|
} |
421 |
|
|
}; |
422 |
|
|
|
423 |
root |
1.2 |
=back |
424 |
root |
1.1 |
|
425 |
|
|
=head2 OPTIMISATION HINTS |
426 |
|
|
|
427 |
root |
1.88 |
=over |
428 |
root |
1.1 |
|
429 |
root |
1.58 |
=item bool ecb_is_constant (expr) |
430 |
root |
1.1 |
|
431 |
root |
1.3 |
Returns true iff the expression can be deduced to be a compile-time |
432 |
|
|
constant, and false otherwise. |
433 |
|
|
|
434 |
|
|
For example, when you have a C<rndm16> function that returns a 16 bit |
435 |
|
|
random number, and you have a function that maps this to a range from |
436 |
root |
1.5 |
0..n-1, then you could use this inline function in a header file: |
437 |
root |
1.3 |
|
438 |
|
|
ecb_inline uint32_t |
439 |
|
|
rndm (uint32_t n) |
440 |
|
|
{ |
441 |
root |
1.6 |
return (n * (uint32_t)rndm16 ()) >> 16; |
442 |
root |
1.3 |
} |
443 |
|
|
|
444 |
|
|
However, for powers of two, you could use a normal mask, but that is only |
445 |
|
|
worth it if, at compile time, you can detect this case. This is the case |
446 |
|
|
when the passed number is a constant and also a power of two (C<n & (n - |
447 |
|
|
1) == 0>): |
448 |
|
|
|
449 |
|
|
ecb_inline uint32_t |
450 |
|
|
rndm (uint32_t n) |
451 |
|
|
{ |
452 |
|
|
return is_constant (n) && !(n & (n - 1)) |
453 |
|
|
? rndm16 () & (num - 1) |
454 |
root |
1.6 |
: (n * (uint32_t)rndm16 ()) >> 16; |
455 |
root |
1.3 |
} |
456 |
|
|
|
457 |
root |
1.62 |
=item ecb_expect (expr, value) |
458 |
root |
1.1 |
|
459 |
root |
1.7 |
Evaluates C<expr> and returns it. In addition, it tells the compiler that |
460 |
|
|
the C<expr> evaluates to C<value> a lot, which can be used for static |
461 |
|
|
branch optimisations. |
462 |
root |
1.1 |
|
463 |
root |
1.27 |
Usually, you want to use the more intuitive C<ecb_expect_true> and |
464 |
|
|
C<ecb_expect_false> functions instead. |
465 |
root |
1.1 |
|
466 |
root |
1.27 |
=item bool ecb_expect_true (cond) |
467 |
root |
1.1 |
|
468 |
root |
1.27 |
=item bool ecb_expect_false (cond) |
469 |
root |
1.1 |
|
470 |
root |
1.7 |
These two functions expect a expression that is true or false and return |
471 |
|
|
C<1> or C<0>, respectively, so when used in the condition of an C<if> or |
472 |
|
|
other conditional statement, it will not change the program: |
473 |
|
|
|
474 |
|
|
/* these two do the same thing */ |
475 |
|
|
if (some_condition) ...; |
476 |
root |
1.27 |
if (ecb_expect_true (some_condition)) ...; |
477 |
root |
1.7 |
|
478 |
root |
1.27 |
However, by using C<ecb_expect_true>, you tell the compiler that the |
479 |
|
|
condition is likely to be true (and for C<ecb_expect_false>, that it is |
480 |
|
|
unlikely to be true). |
481 |
root |
1.7 |
|
482 |
root |
1.9 |
For example, when you check for a null pointer and expect this to be a |
483 |
root |
1.27 |
rare, exceptional, case, then use C<ecb_expect_false>: |
484 |
root |
1.7 |
|
485 |
|
|
void my_free (void *ptr) |
486 |
|
|
{ |
487 |
root |
1.27 |
if (ecb_expect_false (ptr == 0)) |
488 |
root |
1.7 |
return; |
489 |
|
|
} |
490 |
|
|
|
491 |
|
|
Consequent use of these functions to mark away exceptional cases or to |
492 |
|
|
tell the compiler what the hot path through a function is can increase |
493 |
|
|
performance considerably. |
494 |
|
|
|
495 |
root |
1.27 |
You might know these functions under the name C<likely> and C<unlikely> |
496 |
|
|
- while these are common aliases, we find that the expect name is easier |
497 |
|
|
to understand when quickly skimming code. If you wish, you can use |
498 |
|
|
C<ecb_likely> instead of C<ecb_expect_true> and C<ecb_unlikely> instead of |
499 |
|
|
C<ecb_expect_false> - these are simply aliases. |
500 |
|
|
|
501 |
root |
1.7 |
A very good example is in a function that reserves more space for some |
502 |
|
|
memory block (for example, inside an implementation of a string stream) - |
503 |
root |
1.9 |
each time something is added, you have to check for a buffer overrun, but |
504 |
root |
1.7 |
you expect that most checks will turn out to be false: |
505 |
|
|
|
506 |
|
|
/* make sure we have "size" extra room in our buffer */ |
507 |
|
|
ecb_inline void |
508 |
|
|
reserve (int size) |
509 |
|
|
{ |
510 |
root |
1.27 |
if (ecb_expect_false (current + size > end)) |
511 |
root |
1.7 |
real_reserve_method (size); /* presumably noinline */ |
512 |
|
|
} |
513 |
|
|
|
514 |
root |
1.62 |
=item ecb_assume (cond) |
515 |
root |
1.7 |
|
516 |
sf-exg |
1.66 |
Tries to tell the compiler that some condition is true, even if it's not |
517 |
root |
1.65 |
obvious. This is not a function, but a statement: it cannot be used in |
518 |
|
|
another expression. |
519 |
root |
1.7 |
|
520 |
|
|
This can be used to teach the compiler about invariants or other |
521 |
|
|
conditions that might improve code generation, but which are impossible to |
522 |
|
|
deduce form the code itself. |
523 |
|
|
|
524 |
root |
1.27 |
For example, the example reservation function from the C<ecb_expect_false> |
525 |
root |
1.7 |
description could be written thus (only C<ecb_assume> was added): |
526 |
|
|
|
527 |
|
|
ecb_inline void |
528 |
|
|
reserve (int size) |
529 |
|
|
{ |
530 |
root |
1.27 |
if (ecb_expect_false (current + size > end)) |
531 |
root |
1.7 |
real_reserve_method (size); /* presumably noinline */ |
532 |
|
|
|
533 |
|
|
ecb_assume (current + size <= end); |
534 |
|
|
} |
535 |
|
|
|
536 |
|
|
If you then call this function twice, like this: |
537 |
|
|
|
538 |
|
|
reserve (10); |
539 |
|
|
reserve (1); |
540 |
|
|
|
541 |
|
|
Then the compiler I<might> be able to optimise out the second call |
542 |
|
|
completely, as it knows that C<< current + 1 > end >> is false and the |
543 |
|
|
call will never be executed. |
544 |
|
|
|
545 |
root |
1.62 |
=item ecb_unreachable () |
546 |
root |
1.7 |
|
547 |
|
|
This function does nothing itself, except tell the compiler that it will |
548 |
root |
1.9 |
never be executed. Apart from suppressing a warning in some cases, this |
549 |
root |
1.65 |
function can be used to implement C<ecb_assume> or similar functionality. |
550 |
root |
1.7 |
|
551 |
root |
1.62 |
=item ecb_prefetch (addr, rw, locality) |
552 |
root |
1.7 |
|
553 |
|
|
Tells the compiler to try to prefetch memory at the given C<addr>ess |
554 |
root |
1.10 |
for either reading (C<rw> = 0) or writing (C<rw> = 1). A C<locality> of |
555 |
root |
1.7 |
C<0> means that there will only be one access later, C<3> means that |
556 |
|
|
the data will likely be accessed very often, and values in between mean |
557 |
|
|
something... in between. The memory pointed to by the address does not |
558 |
|
|
need to be accessible (it could be a null pointer for example), but C<rw> |
559 |
|
|
and C<locality> must be compile-time constants. |
560 |
|
|
|
561 |
root |
1.65 |
This is a statement, not a function: you cannot use it as part of an |
562 |
|
|
expression. |
563 |
|
|
|
564 |
root |
1.7 |
An obvious way to use this is to prefetch some data far away, in a big |
565 |
root |
1.9 |
array you loop over. This prefetches memory some 128 array elements later, |
566 |
root |
1.7 |
in the hope that it will be ready when the CPU arrives at that location. |
567 |
|
|
|
568 |
|
|
int sum = 0; |
569 |
|
|
|
570 |
|
|
for (i = 0; i < N; ++i) |
571 |
|
|
{ |
572 |
|
|
sum += arr [i] |
573 |
|
|
ecb_prefetch (arr + i + 128, 0, 0); |
574 |
|
|
} |
575 |
|
|
|
576 |
|
|
It's hard to predict how far to prefetch, and most CPUs that can prefetch |
577 |
|
|
are often good enough to predict this kind of behaviour themselves. It |
578 |
|
|
gets more interesting with linked lists, especially when you do some fair |
579 |
|
|
processing on each list element: |
580 |
|
|
|
581 |
|
|
for (node *n = start; n; n = n->next) |
582 |
|
|
{ |
583 |
|
|
ecb_prefetch (n->next, 0, 0); |
584 |
|
|
... do medium amount of work with *n |
585 |
|
|
} |
586 |
|
|
|
587 |
|
|
After processing the node, (part of) the next node might already be in |
588 |
|
|
cache. |
589 |
root |
1.1 |
|
590 |
root |
1.2 |
=back |
591 |
root |
1.1 |
|
592 |
root |
1.36 |
=head2 BIT FIDDLING / BIT WIZARDRY |
593 |
root |
1.1 |
|
594 |
root |
1.88 |
=over |
595 |
root |
1.4 |
|
596 |
root |
1.3 |
=item bool ecb_big_endian () |
597 |
|
|
|
598 |
|
|
=item bool ecb_little_endian () |
599 |
|
|
|
600 |
sf-exg |
1.11 |
These two functions return true if the byte order is big endian |
601 |
|
|
(most-significant byte first) or little endian (least-significant byte |
602 |
|
|
first) respectively. |
603 |
|
|
|
604 |
root |
1.24 |
On systems that are neither, their return values are unspecified. |
605 |
|
|
|
606 |
root |
1.3 |
=item int ecb_ctz32 (uint32_t x) |
607 |
|
|
|
608 |
root |
1.35 |
=item int ecb_ctz64 (uint64_t x) |
609 |
|
|
|
610 |
root |
1.77 |
=item int ecb_ctz (T x) [C++] |
611 |
|
|
|
612 |
sf-exg |
1.11 |
Returns the index of the least significant bit set in C<x> (or |
613 |
root |
1.24 |
equivalently the number of bits set to 0 before the least significant bit |
614 |
root |
1.35 |
set), starting from 0. If C<x> is 0 the result is undefined. |
615 |
|
|
|
616 |
root |
1.36 |
For smaller types than C<uint32_t> you can safely use C<ecb_ctz32>. |
617 |
|
|
|
618 |
root |
1.77 |
The overloaded C++ C<ecb_ctz> function supports C<uint8_t>, C<uint16_t>, |
619 |
|
|
C<uint32_t> and C<uint64_t> types. |
620 |
|
|
|
621 |
root |
1.35 |
For example: |
622 |
sf-exg |
1.11 |
|
623 |
root |
1.15 |
ecb_ctz32 (3) = 0 |
624 |
|
|
ecb_ctz32 (6) = 1 |
625 |
sf-exg |
1.11 |
|
626 |
root |
1.41 |
=item bool ecb_is_pot32 (uint32_t x) |
627 |
|
|
|
628 |
|
|
=item bool ecb_is_pot64 (uint32_t x) |
629 |
|
|
|
630 |
root |
1.77 |
=item bool ecb_is_pot (T x) [C++] |
631 |
|
|
|
632 |
sf-exg |
1.66 |
Returns true iff C<x> is a power of two or C<x == 0>. |
633 |
root |
1.41 |
|
634 |
sf-exg |
1.66 |
For smaller types than C<uint32_t> you can safely use C<ecb_is_pot32>. |
635 |
root |
1.41 |
|
636 |
root |
1.77 |
The overloaded C++ C<ecb_is_pot> function supports C<uint8_t>, C<uint16_t>, |
637 |
|
|
C<uint32_t> and C<uint64_t> types. |
638 |
|
|
|
639 |
root |
1.35 |
=item int ecb_ld32 (uint32_t x) |
640 |
|
|
|
641 |
|
|
=item int ecb_ld64 (uint64_t x) |
642 |
|
|
|
643 |
root |
1.77 |
=item int ecb_ld64 (T x) [C++] |
644 |
|
|
|
645 |
root |
1.35 |
Returns the index of the most significant bit set in C<x>, or the number |
646 |
|
|
of digits the number requires in binary (so that C<< 2**ld <= x < |
647 |
|
|
2**(ld+1) >>). If C<x> is 0 the result is undefined. A common use case is |
648 |
|
|
to compute the integer binary logarithm, i.e. C<floor (log2 (n))>, for |
649 |
|
|
example to see how many bits a certain number requires to be encoded. |
650 |
|
|
|
651 |
|
|
This function is similar to the "count leading zero bits" function, except |
652 |
|
|
that that one returns how many zero bits are "in front" of the number (in |
653 |
|
|
the given data type), while C<ecb_ld> returns how many bits the number |
654 |
|
|
itself requires. |
655 |
|
|
|
656 |
root |
1.36 |
For smaller types than C<uint32_t> you can safely use C<ecb_ld32>. |
657 |
|
|
|
658 |
root |
1.77 |
The overloaded C++ C<ecb_ld> function supports C<uint8_t>, C<uint16_t>, |
659 |
|
|
C<uint32_t> and C<uint64_t> types. |
660 |
|
|
|
661 |
root |
1.3 |
=item int ecb_popcount32 (uint32_t x) |
662 |
|
|
|
663 |
root |
1.35 |
=item int ecb_popcount64 (uint64_t x) |
664 |
|
|
|
665 |
root |
1.77 |
=item int ecb_popcount (T x) [C++] |
666 |
|
|
|
667 |
root |
1.36 |
Returns the number of bits set to 1 in C<x>. |
668 |
|
|
|
669 |
|
|
For smaller types than C<uint32_t> you can safely use C<ecb_popcount32>. |
670 |
|
|
|
671 |
root |
1.77 |
The overloaded C++ C<ecb_popcount> function supports C<uint8_t>, C<uint16_t>, |
672 |
|
|
C<uint32_t> and C<uint64_t> types. |
673 |
|
|
|
674 |
root |
1.36 |
For example: |
675 |
sf-exg |
1.11 |
|
676 |
root |
1.15 |
ecb_popcount32 (7) = 3 |
677 |
|
|
ecb_popcount32 (255) = 8 |
678 |
sf-exg |
1.11 |
|
679 |
root |
1.39 |
=item uint8_t ecb_bitrev8 (uint8_t x) |
680 |
|
|
|
681 |
|
|
=item uint16_t ecb_bitrev16 (uint16_t x) |
682 |
|
|
|
683 |
|
|
=item uint32_t ecb_bitrev32 (uint32_t x) |
684 |
|
|
|
685 |
root |
1.77 |
=item T ecb_bitrev (T x) [C++] |
686 |
|
|
|
687 |
root |
1.39 |
Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1 |
688 |
|
|
and so on. |
689 |
|
|
|
690 |
root |
1.77 |
The overloaded C++ C<ecb_bitrev> function supports C<uint8_t>, C<uint16_t> and C<uint32_t> types. |
691 |
|
|
|
692 |
root |
1.39 |
Example: |
693 |
|
|
|
694 |
|
|
ecb_bitrev8 (0xa7) = 0xea |
695 |
|
|
ecb_bitrev32 (0xffcc4411) = 0x882233ff |
696 |
|
|
|
697 |
root |
1.77 |
=item T ecb_bitrev (T x) [C++] |
698 |
|
|
|
699 |
|
|
Overloaded C++ bitrev function. |
700 |
|
|
|
701 |
|
|
C<T> must be one of C<uint8_t>, C<uint16_t> or C<uint32_t>. |
702 |
|
|
|
703 |
root |
1.8 |
=item uint32_t ecb_bswap16 (uint32_t x) |
704 |
|
|
|
705 |
root |
1.3 |
=item uint32_t ecb_bswap32 (uint32_t x) |
706 |
|
|
|
707 |
root |
1.34 |
=item uint64_t ecb_bswap64 (uint64_t x) |
708 |
sf-exg |
1.13 |
|
709 |
root |
1.78 |
=item T ecb_bswap (T x) |
710 |
|
|
|
711 |
root |
1.34 |
These functions return the value of the 16-bit (32-bit, 64-bit) value |
712 |
|
|
C<x> after reversing the order of bytes (0x11223344 becomes 0x44332211 in |
713 |
|
|
C<ecb_bswap32>). |
714 |
|
|
|
715 |
root |
1.77 |
The overloaded C++ C<ecb_bswap> function supports C<uint8_t>, C<uint16_t>, |
716 |
|
|
C<uint32_t> and C<uint64_t> types. |
717 |
root |
1.76 |
|
718 |
root |
1.34 |
=item uint8_t ecb_rotl8 (uint8_t x, unsigned int count) |
719 |
|
|
|
720 |
|
|
=item uint16_t ecb_rotl16 (uint16_t x, unsigned int count) |
721 |
root |
1.3 |
|
722 |
|
|
=item uint32_t ecb_rotl32 (uint32_t x, unsigned int count) |
723 |
|
|
|
724 |
root |
1.34 |
=item uint64_t ecb_rotl64 (uint64_t x, unsigned int count) |
725 |
|
|
|
726 |
|
|
=item uint8_t ecb_rotr8 (uint8_t x, unsigned int count) |
727 |
|
|
|
728 |
|
|
=item uint16_t ecb_rotr16 (uint16_t x, unsigned int count) |
729 |
|
|
|
730 |
|
|
=item uint32_t ecb_rotr32 (uint32_t x, unsigned int count) |
731 |
|
|
|
732 |
root |
1.33 |
=item uint64_t ecb_rotr64 (uint64_t x, unsigned int count) |
733 |
|
|
|
734 |
root |
1.34 |
These two families of functions return the value of C<x> after rotating |
735 |
|
|
all the bits by C<count> positions to the right (C<ecb_rotr>) or left |
736 |
|
|
(C<ecb_rotl>). |
737 |
sf-exg |
1.11 |
|
738 |
root |
1.85 |
Current GCC/clang versions understand these functions and usually compile |
739 |
|
|
them to "optimal" code (e.g. a single C<rol> or a combination of C<shld> |
740 |
|
|
on x86). |
741 |
root |
1.20 |
|
742 |
root |
1.77 |
=item T ecb_rotl (T x, unsigned int count) [C++] |
743 |
|
|
|
744 |
|
|
=item T ecb_rotr (T x, unsigned int count) [C++] |
745 |
|
|
|
746 |
|
|
Overloaded C++ rotl/rotr functions. |
747 |
|
|
|
748 |
|
|
C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>. |
749 |
|
|
|
750 |
root |
1.3 |
=back |
751 |
root |
1.1 |
|
752 |
root |
1.76 |
=head2 HOST ENDIANNESS CONVERSION |
753 |
|
|
|
754 |
root |
1.88 |
=over |
755 |
root |
1.76 |
|
756 |
|
|
=item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v) |
757 |
|
|
|
758 |
|
|
=item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v) |
759 |
|
|
|
760 |
|
|
=item uint_fast64_t ecb_be_u64_to_host (uint_fast64_t v) |
761 |
|
|
|
762 |
|
|
=item uint_fast16_t ecb_le_u16_to_host (uint_fast16_t v) |
763 |
|
|
|
764 |
|
|
=item uint_fast32_t ecb_le_u32_to_host (uint_fast32_t v) |
765 |
|
|
|
766 |
|
|
=item uint_fast64_t ecb_le_u64_to_host (uint_fast64_t v) |
767 |
|
|
|
768 |
|
|
Convert an unsigned 16, 32 or 64 bit value from big or little endian to host byte order. |
769 |
|
|
|
770 |
|
|
The naming convention is C<ecb_>(C<be>|C<le>)C<_u>C<16|32|64>C<_to_host>, |
771 |
root |
1.79 |
where C<be> and C<le> stand for big endian and little endian, respectively. |
772 |
root |
1.76 |
|
773 |
|
|
=item uint_fast16_t ecb_host_to_be_u16 (uint_fast16_t v) |
774 |
|
|
|
775 |
|
|
=item uint_fast32_t ecb_host_to_be_u32 (uint_fast32_t v) |
776 |
|
|
|
777 |
|
|
=item uint_fast64_t ecb_host_to_be_u64 (uint_fast64_t v) |
778 |
|
|
|
779 |
|
|
=item uint_fast16_t ecb_host_to_le_u16 (uint_fast16_t v) |
780 |
|
|
|
781 |
|
|
=item uint_fast32_t ecb_host_to_le_u32 (uint_fast32_t v) |
782 |
|
|
|
783 |
|
|
=item uint_fast64_t ecb_host_to_le_u64 (uint_fast64_t v) |
784 |
|
|
|
785 |
|
|
Like above, but converts I<from> host byte order to the specified |
786 |
|
|
endianness. |
787 |
|
|
|
788 |
|
|
=back |
789 |
|
|
|
790 |
root |
1.77 |
In C++ the following additional template functions are supported: |
791 |
root |
1.76 |
|
792 |
root |
1.88 |
=over |
793 |
root |
1.76 |
|
794 |
|
|
=item T ecb_be_to_host (T v) |
795 |
|
|
|
796 |
|
|
=item T ecb_le_to_host (T v) |
797 |
|
|
|
798 |
|
|
=item T ecb_host_to_be (T v) |
799 |
|
|
|
800 |
|
|
=item T ecb_host_to_le (T v) |
801 |
|
|
|
802 |
root |
1.86 |
=back |
803 |
|
|
|
804 |
root |
1.77 |
These functions work like their C counterparts, above, but use templates, |
805 |
|
|
which make them useful in generic code. |
806 |
root |
1.76 |
|
807 |
|
|
C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t> |
808 |
|
|
(so unlike their C counterparts, there is a version for C<uint8_t>, which |
809 |
|
|
again can be useful in generic code). |
810 |
|
|
|
811 |
|
|
=head2 UNALIGNED LOAD/STORE |
812 |
|
|
|
813 |
|
|
These function load or store unaligned multi-byte values. |
814 |
|
|
|
815 |
root |
1.88 |
=over |
816 |
root |
1.76 |
|
817 |
|
|
=item uint_fast16_t ecb_peek_u16_u (const void *ptr) |
818 |
|
|
|
819 |
|
|
=item uint_fast32_t ecb_peek_u32_u (const void *ptr) |
820 |
|
|
|
821 |
|
|
=item uint_fast64_t ecb_peek_u64_u (const void *ptr) |
822 |
|
|
|
823 |
|
|
These functions load an unaligned, unsigned 16, 32 or 64 bit value from |
824 |
|
|
memory. |
825 |
|
|
|
826 |
|
|
=item uint_fast16_t ecb_peek_be_u16_u (const void *ptr) |
827 |
|
|
|
828 |
|
|
=item uint_fast32_t ecb_peek_be_u32_u (const void *ptr) |
829 |
|
|
|
830 |
|
|
=item uint_fast64_t ecb_peek_be_u64_u (const void *ptr) |
831 |
|
|
|
832 |
|
|
=item uint_fast16_t ecb_peek_le_u16_u (const void *ptr) |
833 |
|
|
|
834 |
|
|
=item uint_fast32_t ecb_peek_le_u32_u (const void *ptr) |
835 |
|
|
|
836 |
|
|
=item uint_fast64_t ecb_peek_le_u64_u (const void *ptr) |
837 |
|
|
|
838 |
|
|
Like above, but additionally convert from big endian (C<be>) or little |
839 |
|
|
endian (C<le>) byte order to host byte order while doing so. |
840 |
|
|
|
841 |
|
|
=item ecb_poke_u16_u (void *ptr, uint16_t v) |
842 |
|
|
|
843 |
|
|
=item ecb_poke_u32_u (void *ptr, uint32_t v) |
844 |
|
|
|
845 |
|
|
=item ecb_poke_u64_u (void *ptr, uint64_t v) |
846 |
|
|
|
847 |
|
|
These functions store an unaligned, unsigned 16, 32 or 64 bit value to |
848 |
|
|
memory. |
849 |
|
|
|
850 |
|
|
=item ecb_poke_be_u16_u (void *ptr, uint_fast16_t v) |
851 |
|
|
|
852 |
|
|
=item ecb_poke_be_u32_u (void *ptr, uint_fast32_t v) |
853 |
|
|
|
854 |
|
|
=item ecb_poke_be_u64_u (void *ptr, uint_fast64_t v) |
855 |
|
|
|
856 |
|
|
=item ecb_poke_le_u16_u (void *ptr, uint_fast16_t v) |
857 |
|
|
|
858 |
|
|
=item ecb_poke_le_u32_u (void *ptr, uint_fast32_t v) |
859 |
|
|
|
860 |
|
|
=item ecb_poke_le_u64_u (void *ptr, uint_fast64_t v) |
861 |
|
|
|
862 |
|
|
Like above, but additionally convert from host byte order to big endian |
863 |
|
|
(C<be>) or little endian (C<le>) byte order while doing so. |
864 |
|
|
|
865 |
|
|
=back |
866 |
|
|
|
867 |
root |
1.77 |
In C++ the following additional template functions are supported: |
868 |
root |
1.76 |
|
869 |
root |
1.88 |
=over |
870 |
root |
1.76 |
|
871 |
root |
1.80 |
=item T ecb_peek<T> (const void *ptr) |
872 |
root |
1.76 |
|
873 |
root |
1.80 |
=item T ecb_peek_be<T> (const void *ptr) |
874 |
root |
1.76 |
|
875 |
root |
1.80 |
=item T ecb_peek_le<T> (const void *ptr) |
876 |
root |
1.76 |
|
877 |
root |
1.80 |
=item T ecb_peek_u<T> (const void *ptr) |
878 |
root |
1.76 |
|
879 |
root |
1.80 |
=item T ecb_peek_be_u<T> (const void *ptr) |
880 |
root |
1.76 |
|
881 |
root |
1.80 |
=item T ecb_peek_le_u<T> (const void *ptr) |
882 |
root |
1.76 |
|
883 |
|
|
Similarly to their C counterparts, these functions load an unsigned 8, 16, |
884 |
|
|
32 or 64 bit value from memory, with optional conversion from big/little |
885 |
|
|
endian. |
886 |
|
|
|
887 |
root |
1.80 |
Since the type cannot be deduced, it has to be specified explicitly, e.g. |
888 |
root |
1.76 |
|
889 |
|
|
uint_fast16_t v = ecb_peek<uint16_t> (ptr); |
890 |
|
|
|
891 |
|
|
C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>. |
892 |
|
|
|
893 |
|
|
Unlike their C counterparts, these functions support 8 bit quantities |
894 |
|
|
(C<uint8_t>) and also have an aligned version (without the C<_u> prefix), |
895 |
|
|
all of which hopefully makes them more useful in generic code. |
896 |
|
|
|
897 |
|
|
=item ecb_poke (void *ptr, T v) |
898 |
|
|
|
899 |
|
|
=item ecb_poke_be (void *ptr, T v) |
900 |
|
|
|
901 |
|
|
=item ecb_poke_le (void *ptr, T v) |
902 |
|
|
|
903 |
|
|
=item ecb_poke_u (void *ptr, T v) |
904 |
|
|
|
905 |
|
|
=item ecb_poke_be_u (void *ptr, T v) |
906 |
|
|
|
907 |
|
|
=item ecb_poke_le_u (void *ptr, T v) |
908 |
|
|
|
909 |
|
|
Again, similarly to their C counterparts, these functions store an |
910 |
|
|
unsigned 8, 16, 32 or z64 bit value to memory, with optional conversion to |
911 |
|
|
big/little endian. |
912 |
|
|
|
913 |
|
|
C<T> must be one of C<uint8_t>, C<uint16_t>, C<uint32_t> or C<uint64_t>. |
914 |
|
|
|
915 |
|
|
Unlike their C counterparts, these functions support 8 bit quantities |
916 |
|
|
(C<uint8_t>) and also have an aligned version (without the C<_u> prefix), |
917 |
|
|
all of which hopefully makes them more useful in generic code. |
918 |
|
|
|
919 |
|
|
=back |
920 |
|
|
|
921 |
root |
1.89 |
=head2 FAST INTEGER TO STRING |
922 |
|
|
|
923 |
|
|
Libecb defines a set of very fast integer to decimal string (or integer |
924 |
|
|
to ascii, short C<i2a>) functions. These work by converting the integer |
925 |
|
|
to a fixed point representation and then successively multiplying out |
926 |
|
|
the topmost digits. Unlike some other, also very fast, libraries, ecb's |
927 |
|
|
algorithm should be completely branchless per digit, and does not rely on |
928 |
|
|
the presence of special cpu functions (such as clz). |
929 |
|
|
|
930 |
|
|
There is a high level API that takes an C<int32_t>, C<uint32_t>, |
931 |
|
|
C<int64_t> or C<uint64_t> as argument, and a low-level API, which is |
932 |
|
|
harder to use but supports slightly more formatting options. |
933 |
|
|
|
934 |
|
|
=head3 HIGH LEVEL API |
935 |
|
|
|
936 |
|
|
The high level API consists of four functions, one each for C<int32_t>, |
937 |
|
|
C<uint32_t>, C<int64_t> and C<uint64_t>: |
938 |
|
|
|
939 |
|
|
=over |
940 |
|
|
|
941 |
|
|
=item ECB_I2A_I32_DIGITS (=11) |
942 |
|
|
|
943 |
|
|
=item char *ecb_i2a_u32 (char *ptr, uint32_t value) |
944 |
|
|
|
945 |
|
|
Takes an C<uint32_t> I<value> and formats it as a decimal number starting |
946 |
|
|
at I<ptr>, using at most C<ECB_I2A_I32_DIGITS> characters. Returns a |
947 |
|
|
pointer to just after the generated string, where you would normally put |
948 |
|
|
the temrinating C<0> character. This function outputs the minimum number |
949 |
|
|
of digits. |
950 |
|
|
|
951 |
|
|
=item ECB_I2A_U32_DIGITS (=10) |
952 |
|
|
|
953 |
|
|
=item char *ecb_i2a_i32 (char *ptr, int32_t value) |
954 |
|
|
|
955 |
|
|
Same as C<ecb_i2a_u32>, but formats a C<int32_t> value, including a minus |
956 |
|
|
sign if needed. |
957 |
|
|
|
958 |
|
|
=item ECB_I2A_I64_DIGITS (=20) |
959 |
|
|
|
960 |
|
|
=item char *ecb_i2a_u64 (char *ptr, uint64_t value) |
961 |
|
|
|
962 |
|
|
=item ECB_I2A_U64_DIGITS (=21) |
963 |
|
|
|
964 |
|
|
=item char *ecb_i2a_i64 (char *ptr, int64_t value) |
965 |
|
|
|
966 |
|
|
Similar to their 32 bit counterparts, these take a 64 bit argument. |
967 |
|
|
|
968 |
root |
1.90 |
=item ECB_I2A_MAX_DIGITS (=21) |
969 |
root |
1.89 |
|
970 |
|
|
Instead of using a type specific length macro, youi can just use |
971 |
root |
1.90 |
C<ECB_I2A_MAX_DIGITS>, which is good enough for any C<ecb_i2a> function. |
972 |
root |
1.89 |
|
973 |
|
|
=back |
974 |
|
|
|
975 |
|
|
=head3 LOW-LEVEL API |
976 |
|
|
|
977 |
|
|
The functions above use a number of low-level APIs which have some strict |
978 |
|
|
limitaitons, but cna be used as building blocks (study of C<ecb_i2a_i32> |
979 |
|
|
and related cunctions is recommended). |
980 |
|
|
|
981 |
|
|
There are three families of functions: functions that convert a number |
982 |
|
|
to a fixed number of digits with leading zeroes (C<ecb_i2a_0N>, C<0> |
983 |
|
|
for "leading zeroes"), functions that generate up to N digits, skipping |
984 |
|
|
leading zeroes (C<_N>), and functions that can generate more digits, but |
985 |
|
|
the leading digit has limited range (C<_xN>). |
986 |
|
|
|
987 |
|
|
None of the functions deal with negative numbera. |
988 |
|
|
|
989 |
|
|
=over |
990 |
|
|
|
991 |
|
|
=item char *ecb_i2a_02 (char *ptr, uint32_t value) // 32 bit |
992 |
|
|
|
993 |
|
|
=item char *ecb_i2a_03 (char *ptr, uint32_t value) // 32 bit |
994 |
|
|
|
995 |
|
|
=item char *ecb_i2a_04 (char *ptr, uint32_t value) // 32 bit |
996 |
|
|
|
997 |
|
|
=item char *ecb_i2a_05 (char *ptr, uint32_t value) // 64 bit |
998 |
|
|
|
999 |
|
|
=item char *ecb_i2a_06 (char *ptr, uint32_t value) // 64 bit |
1000 |
|
|
|
1001 |
|
|
=item char *ecb_i2a_07 (char *ptr, uint32_t value) // 64 bit |
1002 |
|
|
|
1003 |
|
|
=item char *ecb_i2a_08 (char *ptr, uint32_t value) // 64 bit |
1004 |
|
|
|
1005 |
|
|
=item char *ecb_i2a_09 (char *ptr, uint32_t value) // 64 bit |
1006 |
|
|
|
1007 |
|
|
The C<< ecb_i2a_0I<N> > functions take an unsigned I<value> and convert |
1008 |
|
|
them to exactly I<N> digits, returning a pointer to the first character |
1009 |
|
|
after the digits. The I<value> must be in range. The functions marked with |
1010 |
|
|
I<32 bit> do their calculations internally in 32 bit, the ones marked with |
1011 |
|
|
I<64 bit> internally use 64 bit integers, which might be slow on 32 bit |
1012 |
|
|
architectures (the high level API decides on 32 vs. 64 bit versions using |
1013 |
|
|
C<ECB_64BIT_NATIVE>). |
1014 |
|
|
|
1015 |
|
|
=item char *ecb_i2a_2 (char *ptr, uint32_t value) // 32 bit |
1016 |
|
|
|
1017 |
|
|
=item char *ecb_i2a_3 (char *ptr, uint32_t value) // 32 bit |
1018 |
|
|
|
1019 |
|
|
=item char *ecb_i2a_4 (char *ptr, uint32_t value) // 32 bit |
1020 |
|
|
|
1021 |
|
|
=item char *ecb_i2a_5 (char *ptr, uint32_t value) // 64 bit |
1022 |
|
|
|
1023 |
|
|
=item char *ecb_i2a_6 (char *ptr, uint32_t value) // 64 bit |
1024 |
|
|
|
1025 |
|
|
=item char *ecb_i2a_7 (char *ptr, uint32_t value) // 64 bit |
1026 |
|
|
|
1027 |
|
|
=item char *ecb_i2a_8 (char *ptr, uint32_t value) // 64 bit |
1028 |
|
|
|
1029 |
|
|
=item char *ecb_i2a_9 (char *ptr, uint32_t value) // 64 bit |
1030 |
|
|
|
1031 |
|
|
Similarly, the C<< ecb_i2a_I<N> > functions take an unsigned I<value> |
1032 |
|
|
and convert them to at most I<N> digits, suppressing leading zeroes, and |
1033 |
|
|
returning a pointer to the first character after the digits. |
1034 |
|
|
|
1035 |
|
|
=item ECB_I2A_MAX_X5 (=59074) |
1036 |
|
|
|
1037 |
|
|
=item char *ecb_i2a_x5 (char *ptr, uint32_t value) // 32 bit |
1038 |
|
|
|
1039 |
|
|
=item ECB_I2A_MAX_X10 (=2932500665) |
1040 |
|
|
|
1041 |
|
|
=item char *ecb_i2a_x10 (char *ptr, uint32_t value) // 64 bit |
1042 |
|
|
|
1043 |
|
|
The C<< ecb_i2a_xI<N> >> functions are similar to the C<< ecb_i2a_I<N> > |
1044 |
|
|
functions, but they can generate one digit more, as long as the number |
1045 |
|
|
is within range, which is given by the symbols C<ECB_I2A_MAX_X5> (almost |
1046 |
|
|
16 bit range) and C<ECB_I2A_MAX_X10> (a bit more than 31 bit range), |
1047 |
|
|
respectively. |
1048 |
|
|
|
1049 |
|
|
For example, the sigit part of a 32 bit signed integer just fits into the |
1050 |
|
|
C<ECB_I2A_MAX_X10> range, so while C<ecb_i2a_x10> cannot convert a 10 |
1051 |
|
|
digit number, it can convert all 32 bit signed numbers. Sadly, it's not |
1052 |
|
|
good enough for 32 bit unsigned numbers. |
1053 |
|
|
|
1054 |
|
|
=back |
1055 |
|
|
|
1056 |
root |
1.50 |
=head2 FLOATING POINT FIDDLING |
1057 |
|
|
|
1058 |
root |
1.88 |
=over |
1059 |
root |
1.50 |
|
1060 |
root |
1.71 |
=item ECB_INFINITY [-UECB_NO_LIBM] |
1061 |
root |
1.62 |
|
1062 |
|
|
Evaluates to positive infinity if supported by the platform, otherwise to |
1063 |
|
|
a truly huge number. |
1064 |
|
|
|
1065 |
root |
1.71 |
=item ECB_NAN [-UECB_NO_LIBM] |
1066 |
root |
1.62 |
|
1067 |
|
|
Evaluates to a quiet NAN if supported by the platform, otherwise to |
1068 |
|
|
C<ECB_INFINITY>. |
1069 |
|
|
|
1070 |
root |
1.71 |
=item float ecb_ldexpf (float x, int exp) [-UECB_NO_LIBM] |
1071 |
root |
1.62 |
|
1072 |
|
|
Same as C<ldexpf>, but always available. |
1073 |
|
|
|
1074 |
root |
1.71 |
=item uint32_t ecb_float_to_binary16 (float x) [-UECB_NO_LIBM] |
1075 |
|
|
|
1076 |
root |
1.50 |
=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM] |
1077 |
|
|
|
1078 |
|
|
=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM] |
1079 |
|
|
|
1080 |
|
|
These functions each take an argument in the native C<float> or C<double> |
1081 |
root |
1.71 |
type and return the IEEE 754 bit representation of it (binary16/half, |
1082 |
|
|
binary32/single or binary64/double precision). |
1083 |
root |
1.50 |
|
1084 |
|
|
The bit representation is just as IEEE 754 defines it, i.e. the sign bit |
1085 |
|
|
will be the most significant bit, followed by exponent and mantissa. |
1086 |
|
|
|
1087 |
|
|
This function should work even when the native floating point format isn't |
1088 |
|
|
IEEE compliant, of course at a speed and code size penalty, and of course |
1089 |
|
|
also within reasonable limits (it tries to convert NaNs, infinities and |
1090 |
|
|
denormals, but will likely convert negative zero to positive zero). |
1091 |
|
|
|
1092 |
|
|
On all modern platforms (where C<ECB_STDFP> is true), the compiler should |
1093 |
|
|
be able to optimise away this function completely. |
1094 |
|
|
|
1095 |
|
|
These functions can be helpful when serialising floats to the network - you |
1096 |
root |
1.71 |
can serialise the return value like a normal uint16_t/uint32_t/uint64_t. |
1097 |
root |
1.50 |
|
1098 |
|
|
Another use for these functions is to manipulate floating point values |
1099 |
|
|
directly. |
1100 |
|
|
|
1101 |
|
|
Silly example: toggle the sign bit of a float. |
1102 |
|
|
|
1103 |
|
|
/* On gcc-4.7 on amd64, */ |
1104 |
|
|
/* this results in a single add instruction to toggle the bit, and 4 extra */ |
1105 |
|
|
/* instructions to move the float value to an integer register and back. */ |
1106 |
|
|
|
1107 |
|
|
x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U) |
1108 |
|
|
|
1109 |
root |
1.58 |
=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM] |
1110 |
|
|
|
1111 |
root |
1.50 |
=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM] |
1112 |
|
|
|
1113 |
root |
1.70 |
=item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM] |
1114 |
root |
1.50 |
|
1115 |
sf-exg |
1.59 |
The reverse operation of the previous function - takes the bit |
1116 |
root |
1.71 |
representation of an IEEE binary16, binary32 or binary64 number (half, |
1117 |
|
|
single or double precision) and converts it to the native C<float> or |
1118 |
|
|
C<double> format. |
1119 |
root |
1.50 |
|
1120 |
|
|
This function should work even when the native floating point format isn't |
1121 |
|
|
IEEE compliant, of course at a speed and code size penalty, and of course |
1122 |
|
|
also within reasonable limits (it tries to convert normals and denormals, |
1123 |
|
|
and might be lucky for infinities, and with extraordinary luck, also for |
1124 |
|
|
negative zero). |
1125 |
|
|
|
1126 |
|
|
On all modern platforms (where C<ECB_STDFP> is true), the compiler should |
1127 |
|
|
be able to optimise away this function completely. |
1128 |
|
|
|
1129 |
root |
1.71 |
=item uint16_t ecb_binary32_to_binary16 (uint32_t x) |
1130 |
|
|
|
1131 |
|
|
=item uint32_t ecb_binary16_to_binary32 (uint16_t x) |
1132 |
|
|
|
1133 |
|
|
Convert a IEEE binary32/single precision to binary16/half format, and vice |
1134 |
root |
1.72 |
versa, handling all details (round-to-nearest-even, subnormals, infinity |
1135 |
|
|
and NaNs) correctly. |
1136 |
root |
1.71 |
|
1137 |
|
|
These are functions are available under C<-DECB_NO_LIBM>, since |
1138 |
|
|
they do not rely on the platform floating point format. The |
1139 |
|
|
C<ecb_float_to_binary16> and C<ecb_binary16_to_float> functions are |
1140 |
|
|
usually what you want. |
1141 |
|
|
|
1142 |
root |
1.50 |
=back |
1143 |
|
|
|
1144 |
root |
1.1 |
=head2 ARITHMETIC |
1145 |
|
|
|
1146 |
root |
1.88 |
=over |
1147 |
root |
1.3 |
|
1148 |
root |
1.14 |
=item x = ecb_mod (m, n) |
1149 |
root |
1.3 |
|
1150 |
root |
1.25 |
Returns C<m> modulo C<n>, which is the same as the positive remainder |
1151 |
|
|
of the division operation between C<m> and C<n>, using floored |
1152 |
|
|
division. Unlike the C remainder operator C<%>, this function ensures that |
1153 |
|
|
the return value is always positive and that the two numbers I<m> and |
1154 |
|
|
I<m' = m + i * n> result in the same value modulo I<n> - in other words, |
1155 |
|
|
C<ecb_mod> implements the mathematical modulo operation, which is missing |
1156 |
|
|
in the language. |
1157 |
root |
1.14 |
|
1158 |
sf-exg |
1.23 |
C<n> must be strictly positive (i.e. C<< >= 1 >>), while C<m> must be |
1159 |
root |
1.14 |
negatable, that is, both C<m> and C<-m> must be representable in its |
1160 |
root |
1.30 |
type (this typically excludes the minimum signed integer value, the same |
1161 |
root |
1.25 |
limitation as for C</> and C<%> in C). |
1162 |
sf-exg |
1.11 |
|
1163 |
root |
1.85 |
Current GCC/clang versions compile this into an efficient branchless |
1164 |
|
|
sequence on almost all CPUs. |
1165 |
root |
1.24 |
|
1166 |
|
|
For example, when you want to rotate forward through the members of an |
1167 |
|
|
array for increasing C<m> (which might be negative), then you should use |
1168 |
|
|
C<ecb_mod>, as the C<%> operator might give either negative results, or |
1169 |
|
|
change direction for negative values: |
1170 |
|
|
|
1171 |
|
|
for (m = -100; m <= 100; ++m) |
1172 |
|
|
int elem = myarray [ecb_mod (m, ecb_array_length (myarray))]; |
1173 |
|
|
|
1174 |
sf-exg |
1.37 |
=item x = ecb_div_rd (val, div) |
1175 |
|
|
|
1176 |
|
|
=item x = ecb_div_ru (val, div) |
1177 |
|
|
|
1178 |
|
|
Returns C<val> divided by C<div> rounded down or up, respectively. |
1179 |
|
|
C<val> and C<div> must have integer types and C<div> must be strictly |
1180 |
sf-exg |
1.38 |
positive. Note that these functions are implemented with macros in C |
1181 |
|
|
and with function templates in C++. |
1182 |
sf-exg |
1.37 |
|
1183 |
root |
1.3 |
=back |
1184 |
root |
1.1 |
|
1185 |
|
|
=head2 UTILITY |
1186 |
|
|
|
1187 |
root |
1.88 |
=over |
1188 |
root |
1.3 |
|
1189 |
sf-exg |
1.23 |
=item element_count = ecb_array_length (name) |
1190 |
root |
1.3 |
|
1191 |
sf-exg |
1.13 |
Returns the number of elements in the array C<name>. For example: |
1192 |
|
|
|
1193 |
|
|
int primes[] = { 2, 3, 5, 7, 11 }; |
1194 |
|
|
int sum = 0; |
1195 |
|
|
|
1196 |
|
|
for (i = 0; i < ecb_array_length (primes); i++) |
1197 |
|
|
sum += primes [i]; |
1198 |
|
|
|
1199 |
root |
1.3 |
=back |
1200 |
root |
1.1 |
|
1201 |
root |
1.43 |
=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF |
1202 |
|
|
|
1203 |
|
|
These symbols need to be defined before including F<ecb.h> the first time. |
1204 |
|
|
|
1205 |
root |
1.88 |
=over |
1206 |
root |
1.43 |
|
1207 |
root |
1.51 |
=item ECB_NO_THREADS |
1208 |
root |
1.43 |
|
1209 |
|
|
If F<ecb.h> is never used from multiple threads, then this symbol can |
1210 |
|
|
be defined, in which case memory fences (and similar constructs) are |
1211 |
|
|
completely removed, leading to more efficient code and fewer dependencies. |
1212 |
|
|
|
1213 |
|
|
Setting this symbol to a true value implies C<ECB_NO_SMP>. |
1214 |
|
|
|
1215 |
|
|
=item ECB_NO_SMP |
1216 |
|
|
|
1217 |
|
|
The weaker version of C<ECB_NO_THREADS> - if F<ecb.h> is used from |
1218 |
|
|
multiple threads, but never concurrently (e.g. if the system the program |
1219 |
|
|
runs on has only a single CPU with a single core, no hyperthreading and so |
1220 |
|
|
on), then this symbol can be defined, leading to more efficient code and |
1221 |
|
|
fewer dependencies. |
1222 |
|
|
|
1223 |
root |
1.50 |
=item ECB_NO_LIBM |
1224 |
|
|
|
1225 |
|
|
When defined to C<1>, do not export any functions that might introduce |
1226 |
|
|
dependencies on the math library (usually called F<-lm>) - these are |
1227 |
|
|
marked with [-UECB_NO_LIBM]. |
1228 |
|
|
|
1229 |
sf-exg |
1.69 |
=back |
1230 |
|
|
|
1231 |
root |
1.68 |
=head1 UNDOCUMENTED FUNCTIONALITY |
1232 |
|
|
|
1233 |
|
|
F<ecb.h> is full of undocumented functionality as well, some of which is |
1234 |
|
|
intended to be internal-use only, some of which we forgot to document, and |
1235 |
|
|
some of which we hide because we are not sure we will keep the interface |
1236 |
|
|
stable. |
1237 |
|
|
|
1238 |
|
|
While you are welcome to rummage around and use whatever you find useful |
1239 |
|
|
(we can't stop you), keep in mind that we will change undocumented |
1240 |
|
|
functionality in incompatible ways without thinking twice, while we are |
1241 |
|
|
considerably more conservative with documented things. |
1242 |
|
|
|
1243 |
|
|
=head1 AUTHORS |
1244 |
|
|
|
1245 |
|
|
C<libecb> is designed and maintained by: |
1246 |
|
|
|
1247 |
|
|
Emanuele Giaquinta <e.giaquinta@glauco.it> |
1248 |
|
|
Marc Alexander Lehmann <schmorp@schmorp.de> |
1249 |
|
|
|
1250 |
root |
1.1 |
|