/* Copyright 2013 Google Inc. All Rights Reserved. Distributed under MIT license. See file LICENSE for detail or copy at https://opensource.org/licenses/MIT */ /* Utilities for fast computation of logarithms. */ #ifndef BROTLI_ENC_FAST_LOG_H_ #define BROTLI_ENC_FAST_LOG_H_ #include #include "../common/platform.h" #if defined(__cplusplus) || defined(c_plusplus) extern "C" { #endif static BROTLI_INLINE uint32_t Log2FloorNonZero(size_t n) { #if defined(BROTLI_BSR32) return BROTLI_BSR32((uint32_t)n); #else uint32_t result = 0; while (n >>= 1) result++; return result; #endif } #define BROTLI_LOG2_TABLE_SIZE 256 /* A lookup table for small values of log2(int) to be used in entropy computation. */ BROTLI_INTERNAL extern const BROTLI_MODEL("small") double kBrotliLog2Table[BROTLI_LOG2_TABLE_SIZE]; /* Visual Studio 2012 and Android API levels < 18 do not have the log2() * function defined, so we use log() and a multiplication instead. */ #if !defined(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. */ static BROTLI_INLINE double FastLog2(size_t v) { if (v < BROTLI_LOG2_TABLE_SIZE) { return kBrotliLog2Table[v]; } #if !(BROTLI_HAVE_LOG2) return log((double)v) * LOG_2_INV; #else return log2((double)v); #endif } #if defined(__cplusplus) || defined(c_plusplus) } /* extern "C" */ #endif #endif /* BROTLI_ENC_FAST_LOG_H_ */