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Add HAVE_LOG2 build macro (#783)

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* Add HAVE_LOG2 build macro

Fixes #781

* Rename macro to BROTLI_HAVE_LOG2 and move comment for visibility
This commit is contained in:
Cristi Vîjdea 2020-03-19 11:46:52 +02:00 committed by GitHub
parent 36ac0feaf9
commit f503cb709c
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GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 15 additions and 5 deletions
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5
CMakeLists.txt
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@ -110,13 +110,16 @@ if(NOT LOG2_RES)
CHECK_FUNCTION_EXISTS(log2 LOG2_LIBM_RES)
if(LOG2_LIBM_RES)
set(LIBM_LIBRARY "m")
add_definitions(-DBROTLI_HAVE_LOG2=1)
else()
message(FATAL_ERROR "log2() not found")
add_definitions(-DBROTLI_HAVE_LOG2=0)
endif()
set(CMAKE_REQUIRED_LIBRARIES "${orig_req_libs}")
unset(LOG2_LIBM_RES)
unset(orig_req_libs)
else()
add_definitions(-DBROTLI_HAVE_LOG2=1)
endif()
unset(LOG2_RES)

15
c/enc/fast_log.h
View File

@ -123,6 +123,16 @@ static const float kLog2Table[] = {
7.9943534368588578f
};
/* Visual Studio 2012 and Android API levels < 18 do not have the log2()
* function defined, so we use log() and a multiplication instead. */
#ifndef BROTLI_HAVE_LOG2
#if ((defined(_MSC_VER) && _MSC_VER <= 1700) || (defined(__ANDROID_API__) && __ANDROID_API__ < 18))
#define BROTLI_HAVE_LOG2 0
#else
#define BROTLI_HAVE_LOG2 1
#endif
#endif
#define LOG_2_INV 1.4426950408889634
/* Faster logarithm for small integers, with the property of log2(0) == 0. */
@ -130,10 +140,7 @@ static BROTLI_INLINE double FastLog2(size_t v) {
if (v < sizeof(kLog2Table) / sizeof(kLog2Table[0])) {
return kLog2Table[v];
}
#if (defined(_MSC_VER) && _MSC_VER <= 1700) || \
(defined(__ANDROID_API__) && __ANDROID_API__ < 18)
/* Visual Studio 2012 and Android API levels < 18 do not have the log2()
* function defined, so we use log() and a multiplication instead. */
#if !(BROTLI_HAVE_LOG2)
return log((double)v) * LOG_2_INV;
#else
return log2((double)v);