--- libecb/ecb.pod 2011/08/24 23:28:47 1.37 +++ libecb/ecb.pod 2021/06/22 00:01:15 1.90 @@ -12,14 +12,14 @@ http://software.schmorp.de/pkg/libecb -It mainly provides a number of wrappers around GCC built-ins, together -with replacement functions for other compilers. In addition to this, -it provides a number of other lowlevel C utilities, such as endianness -detection, byte swapping or bit rotations. - -Or in other words, things that should be built into any standard C system, -but aren't, implemented as efficient as possible with GCC, and still -correct with other compilers. +It mainly provides a number of wrappers around many compiler built-ins, +together with replacement functions for other compilers. In addition +to this, it provides a number of other lowlevel C utilities, such as +endianness detection, byte swapping or bit rotations. + +Or in other words, things that should be built into any standard C +system, but aren't, implemented as efficient as possible with GCC (clang, +msvc...), and still correct with other compilers. More might come. @@ -56,44 +56,200 @@ is usually implemented as a macro. Specifically, a "bool" in this manual refers to any kind of boolean value, not a specific type. -=head2 GCC ATTRIBUTES +=head2 TYPES / TYPE SUPPORT -A major part of libecb deals with GCC attributes. These are additional -attributes that you can assign to functions, variables and sometimes even -types - much like C or C in C. - -While GCC allows declarations to show up in many surprising places, -but not in many expected places, the safest way is to put attribute -declarations before the whole declaration: +ecb.h makes sure that the following types are defined (in the expected way): - ecb_const int mysqrt (int a); - ecb_unused int i; + int8_t uint8_ + int16_t uint16_t + int32_t uint32_ + int64_t uint64_t + int_fast8_t uint_fast8_t + int_fast16_t uint_fast16_t + int_fast32_t uint_fast32_t + int_fast64_t uint_fast64_t + intptr_t uintptr_t + +The macro C is defined to the size of a pointer on this +platform (currently C<4> or C<8>) and can be used in preprocessor +expressions. + +For C and C use C/C. + +=head2 LANGUAGE/ENVIRONMENT/COMPILER VERSIONS + +All the following symbols expand to an expression that can be tested in +preprocessor instructions as well as treated as a boolean (use C to +ensure it's either C<0> or C<1> if you need that). + +=over + +=item ECB_C + +True if the implementation defines the C<__STDC__> macro to a true value, +while not claiming to be C++, i..e C, but not C++. + +=item ECB_C99 + +True if the implementation claims to be compliant to C99 (ISO/IEC +9899:1999) or any later version, while not claiming to be C++. + +Note that later versions (ECB_C11) remove core features again (for +example, variable length arrays). + +=item ECB_C11, ECB_C17 + +True if the implementation claims to be compliant to C11/C17 (ISO/IEC +9899:2011, :20187) or any later version, while not claiming to be C++. + +=item ECB_CPP + +True if the implementation defines the C<__cplusplus__> macro to a true +value, which is typically true for C++ compilers. + +=item ECB_CPP11, ECB_CPP14, ECB_CPP17 + +True if the implementation claims to be compliant to C++11/C++14/C++17 +(ISO/IEC 14882:2011, :2014, :2017) or any later version. + +Note that many C++20 features will likely have their own feature test +macros (see e.g. L). + +=item ECB_OPTIMIZE_SIZE + +Is C<1> when the compiler optimizes for size, C<0> otherwise. This symbol +can also be defined before including F, in which case it will be +unchanged. + +=item ECB_GCC_VERSION (major, minor) + +Expands to a true value (suitable for testing by the preprocessor) if the +compiler used is GNU C and the version is the given version, or higher. + +This macro tries to return false on compilers that claim to be GCC +compatible but aren't. + +=item ECB_EXTERN_C + +Expands to C in C++, and a simple C in C. + +This can be used to declare a single external C function: + + ECB_EXTERN_C int printf (const char *format, ...); + +=item ECB_EXTERN_C_BEG / ECB_EXTERN_C_END + +These two macros can be used to wrap multiple C definitions - +they expand to nothing in C. + +They are most useful in header files: + + ECB_EXTERN_C_BEG + + int mycfun1 (int x); + int mycfun2 (int x); + + ECB_EXTERN_C_END + +=item ECB_STDFP + +If this evaluates to a true value (suitable for testing by the +preprocessor), then C and C use IEEE 754 single/binary32 +and double/binary64 representations internally I the endianness of +both types match the endianness of C and C. -For variables, it is often nicer to put the attribute after the name, and -avoid multiple declarations using commas: +This means you can just copy the bits of a C (or C) to an +C (or C) and get the raw IEEE 754 bit representation +without having to think about format or endianness. - int i ecb_unused; +This is true for basically all modern platforms, although F might +not be able to deduce this correctly everywhere and might err on the safe +side. -=over 4 +=item ECB_64BIT_NATIVE -=item ecb_attribute ((attrs...)) +Evaluates to a true value (suitable for both preprocessor and C code +testing) if 64 bit integer types on this architecture are evaluated +"natively", that is, with similar speeds as 32 bit integerss. While 64 bit +integer support is very common (and in fatc required by libecb), 32 bit +cpus have to emulate operations on them, so you might want to avoid them. -A simple wrapper that expands to C<__attribute__((attrs))> on GCC, and to -nothing on other compilers, so the effect is that only GCC sees these. +=item ECB_AMD64, ECB_AMD64_X32 -Example: use the C attribute on a function. +These two macros are defined to C<1> on the x86_64/amd64 ABI and the X32 +ABI, respectively, and undefined elsewhere. - ecb_attribute((__deprecated__)) void - do_not_use_me_anymore (void); +The designers of the new X32 ABI for some inexplicable reason decided to +make it look exactly like amd64, even though it's completely incompatible +to that ABI, breaking about every piece of software that assumed that +C<__x86_64> stands for, well, the x86-64 ABI, making these macros +necessary. + +=back + +=head2 MACRO TRICKERY + +=over + +=item ECB_CONCAT (a, b) + +Expands any macros in C and C, then concatenates the result to form +a single token. This is mainly useful to form identifiers from components, +e.g.: + + #define S1 str + #define S2 cpy + + ECB_CONCAT (S1, S2)(dst, src); // == strcpy (dst, src); + +=item ECB_STRINGIFY (arg) + +Expands any macros in C and returns the stringified version of +it. This is mainly useful to get the contents of a macro in string form, +e.g.: + + #define SQL_LIMIT 100 + sql_exec ("select * from table limit " ECB_STRINGIFY (SQL_LIMIT)); + +=item ECB_STRINGIFY_EXPR (expr) + +Like C, but additionally evaluates C to make sure it +is a valid expression. This is useful to catch typos or cases where the +macro isn't available: + + #include + + ECB_STRINGIFY (EDOM); // "33" (on my system at least) + ECB_STRINGIFY_EXPR (EDOM); // "33" + + // now imagine we had a typo: + + ECB_STRINGIFY (EDAM); // "EDAM" + ECB_STRINGIFY_EXPR (EDAM); // error: EDAM undefined + +=back + +=head2 ATTRIBUTES + +A major part of libecb deals with additional attributes that can be +assigned to functions, variables and sometimes even types - much like +C or C in C. They are implemented using either GCC +attributes or other compiler/language specific features. Attributes +declarations must be put before the whole declaration: + + ecb_const int mysqrt (int a); + ecb_unused int i; + +=over =item ecb_unused Marks a function or a variable as "unused", which simply suppresses a -warning by GCC when it detects it as unused. This is useful when you e.g. -declare a variable but do not always use it: +warning by the compiler when it detects it as unused. This is useful when +you e.g. declare a variable but do not always use it: { - int var ecb_unused; + ecb_unused int var; #ifdef SOMECONDITION var = ...; @@ -103,12 +259,22 @@ #endif } +=item ecb_deprecated + +Similar to C, but marks a function, variable or type as +deprecated. This makes some compilers warn when the type is used. + +=item ecb_deprecated_message (message) + +Same as C, but if possible, the specified diagnostic is +used instead of a generic depreciation message when the object is being +used. + =item ecb_inline -This is not actually an attribute, but you use it like one. It expands -either to C or to just C, if inline isn't -supported. It should be used to declare functions that should be inlined, -for code size or speed reasons. +Expands either to (a compiler-specific equivalent of) C or +to just C, if inline isn't supported. It should be used to declare +functions that should be inlined, for code size or speed reasons. Example: inline this function, it surely will reduce codesize. @@ -120,7 +286,7 @@ =item ecb_noinline -Prevent a function from being inlined - it might be optimised away, but +Prevents a function from being inlined - it might be optimised away, but not inlined into other functions. This is useful if you know your function is rarely called and large enough for inlining not to be helpful. @@ -140,6 +306,27 @@ In this case, the compiler would probably be smart enough to deduce it on its own, so this is mainly useful for declarations. +=item ecb_restrict + +Expands to the C keyword or equivalent on compilers that support +them, and to nothing on others. Must be specified on a pointer type or +an array index to indicate that the memory doesn't alias with any other +restricted pointer in the same scope. + +Example: multiply a vector, and allow the compiler to parallelise the +loop, because it knows it doesn't overwrite input values. + + void + multiply (ecb_restrict float *src, + ecb_restrict float *dst, + int len, float factor) + { + int i; + + for (i = 0; i < len; ++i) + dst [i] = src [i] * factor; + } + =item ecb_const Declares that the function only depends on the values of its arguments, @@ -209,7 +396,7 @@ =item ecb_artificial Declares the function as "artificial", in this case meaning that this -function is not really mean to be a function, but more like an accessor +function is not really meant to be a function, but more like an accessor - many methods in C++ classes are mere accessor functions, and having a crash reported in such a method, or single-stepping through them, is not usually so helpful, especially when it's inlined to just a few instructions. @@ -237,9 +424,9 @@ =head2 OPTIMISATION HINTS -=over 4 +=over -=item bool ecb_is_constant(expr) +=item bool ecb_is_constant (expr) Returns true iff the expression can be deduced to be a compile-time constant, and false otherwise. @@ -267,7 +454,7 @@ : (n * (uint32_t)rndm16 ()) >> 16; } -=item bool ecb_expect (expr, value) +=item ecb_expect (expr, value) Evaluates C and returns it. In addition, it tells the compiler that the C evaluates to C a lot, which can be used for static @@ -324,10 +511,11 @@ real_reserve_method (size); /* presumably noinline */ } -=item bool ecb_assume (cond) +=item ecb_assume (cond) -Try to tell the compiler that some condition is true, even if it's not -obvious. +Tries to tell the compiler that some condition is true, even if it's not +obvious. This is not a function, but a statement: it cannot be used in +another expression. This can be used to teach the compiler about invariants or other conditions that might improve code generation, but which are impossible to @@ -354,13 +542,13 @@ completely, as it knows that C<< current + 1 > end >> is false and the call will never be executed. -=item bool ecb_unreachable () +=item ecb_unreachable () This function does nothing itself, except tell the compiler that it will never be executed. Apart from suppressing a warning in some cases, this -function can be used to implement C or similar functions. +function can be used to implement C or similar functionality. -=item bool ecb_prefetch (addr, rw, locality) +=item ecb_prefetch (addr, rw, locality) Tells the compiler to try to prefetch memory at the given Cess for either reading (C = 0) or writing (C = 1). A C of @@ -370,6 +558,9 @@ need to be accessible (it could be a null pointer for example), but C and C must be compile-time constants. +This is a statement, not a function: you cannot use it as part of an +expression. + An obvious way to use this is to prefetch some data far away, in a big array you loop over. This prefetches memory some 128 array elements later, in the hope that it will be ready when the CPU arrives at that location. @@ -400,7 +591,7 @@ =head2 BIT FIDDLING / BIT WIZARDRY -=over 4 +=over =item bool ecb_big_endian () @@ -416,21 +607,41 @@ =item int ecb_ctz64 (uint64_t x) +=item int ecb_ctz (T x) [C++] + Returns the index of the least significant bit set in C (or equivalently the number of bits set to 0 before the least significant bit set), starting from 0. If C is 0 the result is undefined. For smaller types than C you can safely use C. +The overloaded C++ C function supports C, C, +C and C types. + For example: ecb_ctz32 (3) = 0 ecb_ctz32 (6) = 1 +=item bool ecb_is_pot32 (uint32_t x) + +=item bool ecb_is_pot64 (uint32_t x) + +=item bool ecb_is_pot (T x) [C++] + +Returns true iff C is a power of two or C. + +For smaller types than C you can safely use C. + +The overloaded C++ C function supports C, C, +C and C types. + =item int ecb_ld32 (uint32_t x) =item int ecb_ld64 (uint64_t x) +=item int ecb_ld64 (T x) [C++] + Returns the index of the most significant bit set in C, or the number of digits the number requires in binary (so that C<< 2**ld <= x < 2**(ld+1) >>). If C is 0 the result is undefined. A common use case is @@ -444,29 +655,66 @@ For smaller types than C you can safely use C. +The overloaded C++ C function supports C, C, +C and C types. + =item int ecb_popcount32 (uint32_t x) =item int ecb_popcount64 (uint64_t x) +=item int ecb_popcount (T x) [C++] + Returns the number of bits set to 1 in C. For smaller types than C you can safely use C. +The overloaded C++ C function supports C, C, +C and C types. + For example: ecb_popcount32 (7) = 3 ecb_popcount32 (255) = 8 +=item uint8_t ecb_bitrev8 (uint8_t x) + +=item uint16_t ecb_bitrev16 (uint16_t x) + +=item uint32_t ecb_bitrev32 (uint32_t x) + +=item T ecb_bitrev (T x) [C++] + +Reverses the bits in x, i.e. the MSB becomes the LSB, MSB-1 becomes LSB+1 +and so on. + +The overloaded C++ C function supports C, C and C types. + +Example: + + ecb_bitrev8 (0xa7) = 0xea + ecb_bitrev32 (0xffcc4411) = 0x882233ff + +=item T ecb_bitrev (T x) [C++] + +Overloaded C++ bitrev function. + +C must be one of C, C or C. + =item uint32_t ecb_bswap16 (uint32_t x) =item uint32_t ecb_bswap32 (uint32_t x) =item uint64_t ecb_bswap64 (uint64_t x) +=item T ecb_bswap (T x) + These functions return the value of the 16-bit (32-bit, 64-bit) value C after reversing the order of bytes (0x11223344 becomes 0x44332211 in C). +The overloaded C++ C function supports C, C, +C and C types. + =item uint8_t ecb_rotl8 (uint8_t x, unsigned int count) =item uint16_t ecb_rotl16 (uint16_t x, unsigned int count) @@ -487,15 +735,415 @@ all the bits by C positions to the right (C) or left (C). -Current GCC versions understand these functions and usually compile them -to "optimal" code (e.g. a single C or a combination of C on -x86). +Current GCC/clang versions understand these functions and usually compile +them to "optimal" code (e.g. a single C or a combination of C +on x86). + +=item T ecb_rotl (T x, unsigned int count) [C++] + +=item T ecb_rotr (T x, unsigned int count) [C++] + +Overloaded C++ rotl/rotr functions. + +C must be one of C, C, C or C. + +=back + +=head2 HOST ENDIANNESS CONVERSION + +=over + +=item uint_fast16_t ecb_be_u16_to_host (uint_fast16_t v) + +=item uint_fast32_t ecb_be_u32_to_host (uint_fast32_t v) + +=item uint_fast64_t ecb_be_u64_to_host (uint_fast64_t v) + +=item uint_fast16_t ecb_le_u16_to_host (uint_fast16_t v) + +=item uint_fast32_t ecb_le_u32_to_host (uint_fast32_t v) + +=item uint_fast64_t ecb_le_u64_to_host (uint_fast64_t v) + +Convert an unsigned 16, 32 or 64 bit value from big or little endian to host byte order. + +The naming convention is C(C|C)C<_u>C<16|32|64>C<_to_host>, +where C and C stand for big endian and little endian, respectively. + +=item uint_fast16_t ecb_host_to_be_u16 (uint_fast16_t v) + +=item uint_fast32_t ecb_host_to_be_u32 (uint_fast32_t v) + +=item uint_fast64_t ecb_host_to_be_u64 (uint_fast64_t v) + +=item uint_fast16_t ecb_host_to_le_u16 (uint_fast16_t v) + +=item uint_fast32_t ecb_host_to_le_u32 (uint_fast32_t v) + +=item uint_fast64_t ecb_host_to_le_u64 (uint_fast64_t v) + +Like above, but converts I host byte order to the specified +endianness. + +=back + +In C++ the following additional template functions are supported: + +=over + +=item T ecb_be_to_host (T v) + +=item T ecb_le_to_host (T v) + +=item T ecb_host_to_be (T v) + +=item T ecb_host_to_le (T v) + +=back + +These functions work like their C counterparts, above, but use templates, +which make them useful in generic code. + +C must be one of C, C, C or C +(so unlike their C counterparts, there is a version for C, which +again can be useful in generic code). + +=head2 UNALIGNED LOAD/STORE + +These function load or store unaligned multi-byte values. + +=over + +=item uint_fast16_t ecb_peek_u16_u (const void *ptr) + +=item uint_fast32_t ecb_peek_u32_u (const void *ptr) + +=item uint_fast64_t ecb_peek_u64_u (const void *ptr) + +These functions load an unaligned, unsigned 16, 32 or 64 bit value from +memory. + +=item uint_fast16_t ecb_peek_be_u16_u (const void *ptr) + +=item uint_fast32_t ecb_peek_be_u32_u (const void *ptr) + +=item uint_fast64_t ecb_peek_be_u64_u (const void *ptr) + +=item uint_fast16_t ecb_peek_le_u16_u (const void *ptr) + +=item uint_fast32_t ecb_peek_le_u32_u (const void *ptr) + +=item uint_fast64_t ecb_peek_le_u64_u (const void *ptr) + +Like above, but additionally convert from big endian (C) or little +endian (C) byte order to host byte order while doing so. + +=item ecb_poke_u16_u (void *ptr, uint16_t v) + +=item ecb_poke_u32_u (void *ptr, uint32_t v) + +=item ecb_poke_u64_u (void *ptr, uint64_t v) + +These functions store an unaligned, unsigned 16, 32 or 64 bit value to +memory. + +=item ecb_poke_be_u16_u (void *ptr, uint_fast16_t v) + +=item ecb_poke_be_u32_u (void *ptr, uint_fast32_t v) + +=item ecb_poke_be_u64_u (void *ptr, uint_fast64_t v) + +=item ecb_poke_le_u16_u (void *ptr, uint_fast16_t v) + +=item ecb_poke_le_u32_u (void *ptr, uint_fast32_t v) + +=item ecb_poke_le_u64_u (void *ptr, uint_fast64_t v) + +Like above, but additionally convert from host byte order to big endian +(C) or little endian (C) byte order while doing so. + +=back + +In C++ the following additional template functions are supported: + +=over + +=item T ecb_peek (const void *ptr) + +=item T ecb_peek_be (const void *ptr) + +=item T ecb_peek_le (const void *ptr) + +=item T ecb_peek_u (const void *ptr) + +=item T ecb_peek_be_u (const void *ptr) + +=item T ecb_peek_le_u (const void *ptr) + +Similarly to their C counterparts, these functions load an unsigned 8, 16, +32 or 64 bit value from memory, with optional conversion from big/little +endian. + +Since the type cannot be deduced, it has to be specified explicitly, e.g. + + uint_fast16_t v = ecb_peek (ptr); + +C must be one of C, C, C or C. + +Unlike their C counterparts, these functions support 8 bit quantities +(C) and also have an aligned version (without the C<_u> prefix), +all of which hopefully makes them more useful in generic code. + +=item ecb_poke (void *ptr, T v) + +=item ecb_poke_be (void *ptr, T v) + +=item ecb_poke_le (void *ptr, T v) + +=item ecb_poke_u (void *ptr, T v) + +=item ecb_poke_be_u (void *ptr, T v) + +=item ecb_poke_le_u (void *ptr, T v) + +Again, similarly to their C counterparts, these functions store an +unsigned 8, 16, 32 or z64 bit value to memory, with optional conversion to +big/little endian. + +C must be one of C, C, C or C. + +Unlike their C counterparts, these functions support 8 bit quantities +(C) and also have an aligned version (without the C<_u> prefix), +all of which hopefully makes them more useful in generic code. + +=back + +=head2 FAST INTEGER TO STRING + +Libecb defines a set of very fast integer to decimal string (or integer +to ascii, short C) functions. These work by converting the integer +to a fixed point representation and then successively multiplying out +the topmost digits. Unlike some other, also very fast, libraries, ecb's +algorithm should be completely branchless per digit, and does not rely on +the presence of special cpu functions (such as clz). + +There is a high level API that takes an C, C, +C or C as argument, and a low-level API, which is +harder to use but supports slightly more formatting options. + +=head3 HIGH LEVEL API + +The high level API consists of four functions, one each for C, +C, C and C: + +=over + +=item ECB_I2A_I32_DIGITS (=11) + +=item char *ecb_i2a_u32 (char *ptr, uint32_t value) + +Takes an C I and formats it as a decimal number starting +at I, using at most C characters. Returns a +pointer to just after the generated string, where you would normally put +the temrinating C<0> character. This function outputs the minimum number +of digits. + +=item ECB_I2A_U32_DIGITS (=10) + +=item char *ecb_i2a_i32 (char *ptr, int32_t value) + +Same as C, but formats a C value, including a minus +sign if needed. + +=item ECB_I2A_I64_DIGITS (=20) + +=item char *ecb_i2a_u64 (char *ptr, uint64_t value) + +=item ECB_I2A_U64_DIGITS (=21) + +=item char *ecb_i2a_i64 (char *ptr, int64_t value) + +Similar to their 32 bit counterparts, these take a 64 bit argument. + +=item ECB_I2A_MAX_DIGITS (=21) + +Instead of using a type specific length macro, youi can just use +C, which is good enough for any C function. + +=back + +=head3 LOW-LEVEL API + +The functions above use a number of low-level APIs which have some strict +limitaitons, but cna be used as building blocks (study of C +and related cunctions is recommended). + +There are three families of functions: functions that convert a number +to a fixed number of digits with leading zeroes (C, C<0> +for "leading zeroes"), functions that generate up to N digits, skipping +leading zeroes (C<_N>), and functions that can generate more digits, but +the leading digit has limited range (C<_xN>). + +None of the functions deal with negative numbera. + +=over + +=item char *ecb_i2a_02 (char *ptr, uint32_t value) // 32 bit + +=item char *ecb_i2a_03 (char *ptr, uint32_t value) // 32 bit + +=item char *ecb_i2a_04 (char *ptr, uint32_t value) // 32 bit + +=item char *ecb_i2a_05 (char *ptr, uint32_t value) // 64 bit + +=item char *ecb_i2a_06 (char *ptr, uint32_t value) // 64 bit + +=item char *ecb_i2a_07 (char *ptr, uint32_t value) // 64 bit + +=item char *ecb_i2a_08 (char *ptr, uint32_t value) // 64 bit + +=item char *ecb_i2a_09 (char *ptr, uint32_t value) // 64 bit + +The C<< ecb_i2a_0I > functions take an unsigned I and convert +them to exactly I digits, returning a pointer to the first character +after the digits. The I must be in range. The functions marked with +I<32 bit> do their calculations internally in 32 bit, the ones marked with +I<64 bit> internally use 64 bit integers, which might be slow on 32 bit +architectures (the high level API decides on 32 vs. 64 bit versions using +C). + +=item char *ecb_i2a_2 (char *ptr, uint32_t value) // 32 bit + +=item char *ecb_i2a_3 (char *ptr, uint32_t value) // 32 bit + +=item char *ecb_i2a_4 (char *ptr, uint32_t value) // 32 bit + +=item char *ecb_i2a_5 (char *ptr, uint32_t value) // 64 bit + +=item char *ecb_i2a_6 (char *ptr, uint32_t value) // 64 bit + +=item char *ecb_i2a_7 (char *ptr, uint32_t value) // 64 bit + +=item char *ecb_i2a_8 (char *ptr, uint32_t value) // 64 bit + +=item char *ecb_i2a_9 (char *ptr, uint32_t value) // 64 bit + +Similarly, the C<< ecb_i2a_I > functions take an unsigned I +and convert them to at most I digits, suppressing leading zeroes, and +returning a pointer to the first character after the digits. + +=item ECB_I2A_MAX_X5 (=59074) + +=item char *ecb_i2a_x5 (char *ptr, uint32_t value) // 32 bit + +=item ECB_I2A_MAX_X10 (=2932500665) + +=item char *ecb_i2a_x10 (char *ptr, uint32_t value) // 64 bit + +The C<< ecb_i2a_xI >> functions are similar to the C<< ecb_i2a_I > +functions, but they can generate one digit more, as long as the number +is within range, which is given by the symbols C (almost +16 bit range) and C (a bit more than 31 bit range), +respectively. + +For example, the sigit part of a 32 bit signed integer just fits into the +C range, so while C cannot convert a 10 +digit number, it can convert all 32 bit signed numbers. Sadly, it's not +good enough for 32 bit unsigned numbers. + +=back + +=head2 FLOATING POINT FIDDLING + +=over + +=item ECB_INFINITY [-UECB_NO_LIBM] + +Evaluates to positive infinity if supported by the platform, otherwise to +a truly huge number. + +=item ECB_NAN [-UECB_NO_LIBM] + +Evaluates to a quiet NAN if supported by the platform, otherwise to +C. + +=item float ecb_ldexpf (float x, int exp) [-UECB_NO_LIBM] + +Same as C, but always available. + +=item uint32_t ecb_float_to_binary16 (float x) [-UECB_NO_LIBM] + +=item uint32_t ecb_float_to_binary32 (float x) [-UECB_NO_LIBM] + +=item uint64_t ecb_double_to_binary64 (double x) [-UECB_NO_LIBM] + +These functions each take an argument in the native C or C +type and return the IEEE 754 bit representation of it (binary16/half, +binary32/single or binary64/double precision). + +The bit representation is just as IEEE 754 defines it, i.e. the sign bit +will be the most significant bit, followed by exponent and mantissa. + +This function should work even when the native floating point format isn't +IEEE compliant, of course at a speed and code size penalty, and of course +also within reasonable limits (it tries to convert NaNs, infinities and +denormals, but will likely convert negative zero to positive zero). + +On all modern platforms (where C is true), the compiler should +be able to optimise away this function completely. + +These functions can be helpful when serialising floats to the network - you +can serialise the return value like a normal uint16_t/uint32_t/uint64_t. + +Another use for these functions is to manipulate floating point values +directly. + +Silly example: toggle the sign bit of a float. + + /* On gcc-4.7 on amd64, */ + /* this results in a single add instruction to toggle the bit, and 4 extra */ + /* instructions to move the float value to an integer register and back. */ + + x = ecb_binary32_to_float (ecb_float_to_binary32 (x) ^ 0x80000000U) + +=item float ecb_binary16_to_float (uint16_t x) [-UECB_NO_LIBM] + +=item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM] + +=item double ecb_binary64_to_double (uint64_t x) [-UECB_NO_LIBM] + +The reverse operation of the previous function - takes the bit +representation of an IEEE binary16, binary32 or binary64 number (half, +single or double precision) and converts it to the native C or +C format. + +This function should work even when the native floating point format isn't +IEEE compliant, of course at a speed and code size penalty, and of course +also within reasonable limits (it tries to convert normals and denormals, +and might be lucky for infinities, and with extraordinary luck, also for +negative zero). + +On all modern platforms (where C is true), the compiler should +be able to optimise away this function completely. + +=item uint16_t ecb_binary32_to_binary16 (uint32_t x) + +=item uint32_t ecb_binary16_to_binary32 (uint16_t x) + +Convert a IEEE binary32/single precision to binary16/half format, and vice +versa, handling all details (round-to-nearest-even, subnormals, infinity +and NaNs) correctly. + +These are functions are available under C<-DECB_NO_LIBM>, since +they do not rely on the platform floating point format. The +C and C functions are +usually what you want. =back =head2 ARITHMETIC -=over 4 +=over =item x = ecb_mod (m, n) @@ -512,8 +1160,8 @@ type (this typically excludes the minimum signed integer value, the same limitation as for C and C<%> in C). -Current GCC versions compile this into an efficient branchless sequence on -almost all CPUs. +Current GCC/clang versions compile this into an efficient branchless +sequence on almost all CPUs. For example, when you want to rotate forward through the members of an array for increasing C (which might be negative), then you should use @@ -529,13 +1177,14 @@ Returns C divided by C
rounded down or up, respectively. C and C
must have integer types and C
must be strictly -positive. +positive. Note that these functions are implemented with macros in C +and with function templates in C++. =back =head2 UTILITY -=over 4 +=over =item element_count = ecb_array_length (name) @@ -549,4 +1198,53 @@ =back +=head2 SYMBOLS GOVERNING COMPILATION OF ECB.H ITSELF + +These symbols need to be defined before including F the first time. + +=over + +=item ECB_NO_THREADS + +If F is never used from multiple threads, then this symbol can +be defined, in which case memory fences (and similar constructs) are +completely removed, leading to more efficient code and fewer dependencies. + +Setting this symbol to a true value implies C. + +=item ECB_NO_SMP + +The weaker version of C - if F is used from +multiple threads, but never concurrently (e.g. if the system the program +runs on has only a single CPU with a single core, no hyperthreading and so +on), then this symbol can be defined, leading to more efficient code and +fewer dependencies. + +=item ECB_NO_LIBM + +When defined to C<1>, do not export any functions that might introduce +dependencies on the math library (usually called F<-lm>) - these are +marked with [-UECB_NO_LIBM]. + +=back + +=head1 UNDOCUMENTED FUNCTIONALITY + +F is full of undocumented functionality as well, some of which is +intended to be internal-use only, some of which we forgot to document, and +some of which we hide because we are not sure we will keep the interface +stable. + +While you are welcome to rummage around and use whatever you find useful +(we can't stop you), keep in mind that we will change undocumented +functionality in incompatible ways without thinking twice, while we are +considerably more conservative with documented things. + +=head1 AUTHORS + +C is designed and maintained by: + + Emanuele Giaquinta + Marc Alexander Lehmann +