--- libecb/ecb.pod 2015/01/26 12:04:56 1.59 +++ libecb/ecb.pod 2015/11/21 16:53:50 1.71 @@ -70,7 +70,7 @@ For C and C use C. -=head2 LANGUAGE/COMPILER VERSIONS +=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 @@ -165,36 +165,60 @@ =back -=head2 GCC ATTRIBUTES +=head2 MACRO TRICKERY -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: +=over 4 - ecb_const int mysqrt (int a); - ecb_unused int i; +=item ECB_CONCAT (a, b) -For variables, it is often nicer to put the attribute after the name, and -avoid multiple declarations using commas: +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.: - int i ecb_unused; + #define S1 str + #define S2 cpy -=over 4 + ECB_CONCAT (S1, S2)(dst, src); // == strcpy (dst, src); + +=item ECB_STRINGIFY (arg) -=item ecb_attribute ((attrs...)) +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.: -A simple wrapper that expands to C<__attribute__((attrs))> on GCC 3.1+ and -Clang 2.8+, and to nothing on other compilers, so the effect is that only -GCC and Clang see these. + #define SQL_LIMIT 100 + sql_exec ("select * from table limit " ECB_STRINGIFY (SQL_LIMIT)); -Example: use the C attribute on a function. +=item ECB_STRINGIFY_EXPR (expr) - ecb_attribute((__deprecated__)) void - do_not_use_me_anymore (void); +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 4 =item ecb_unused @@ -203,7 +227,7 @@ declare a variable but do not always use it: { - int var ecb_unused; + ecb_unused int var; #ifdef SOMECONDITION var = ...; @@ -218,12 +242,17 @@ 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 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. @@ -235,7 +264,7 @@ =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. @@ -266,8 +295,8 @@ loop, because it knows it doesn't overwrite input values. void - multiply (float *ecb_restrict src, - float *ecb_restrict dst, + multiply (ecb_restrict float *src, + ecb_restrict float *dst, int len, float factor) { int i; @@ -403,7 +432,7 @@ : (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 @@ -460,10 +489,11 @@ 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 @@ -490,13 +520,13 @@ 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 @@ -506,6 +536,9 @@ 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. @@ -567,9 +600,9 @@ =item bool ecb_is_pot64 (uint32_t x) -Return true iff C is a power of two or C. +Returns true iff C is a power of two or C. -For smaller types then C you can safely use C. +For smaller types than C you can safely use C. =item int ecb_ld32 (uint32_t x) @@ -655,12 +688,29 @@ =over 4 +=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. +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. @@ -674,7 +724,7 @@ 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 uint32_t/uint64_t. +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. @@ -691,11 +741,12 @@ =item float ecb_binary32_to_float (uint32_t x) [-UECB_NO_LIBM] -=item double ecb_binary32_to_double (uint64_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 and -converts it to the native C or C format. +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 @@ -706,6 +757,19 @@ 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-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 @@ -795,4 +859,23 @@ =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 +