1/* 2 * Copyright (c) 2010 The WebM project authors. All Rights Reserved. 3 * 4 * Use of this source code is governed by a BSD-style license 5 * that can be found in the LICENSE file in the root of the source 6 * tree. An additional intellectual property rights grant can be found 7 * in the file PATENTS. All contributing project authors may 8 * be found in the AUTHORS file in the root of the source tree. 9 */ 10 11#ifndef VPX_PORTS_BITOPS_H_ 12#define VPX_PORTS_BITOPS_H_ 13 14#include <assert.h> 15 16#include "vpx_ports/msvc.h" 17 18#ifdef _MSC_VER 19#if defined(_M_X64) || defined(_M_IX86) 20#include <intrin.h> 21#define USE_MSC_INTRINSICS 22#endif 23#endif 24 25#ifdef __cplusplus 26extern "C" { 27#endif 28 29// These versions of get_msb() are only valid when n != 0 because all 30// of the optimized versions are undefined when n == 0: 31// https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html 32 33// use GNU builtins where available. 34#if defined(__GNUC__) && \ 35 ((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4) 36static INLINE int get_msb(unsigned int n) { 37 assert(n != 0); 38 return 31 ^ __builtin_clz(n); 39} 40#elif defined(USE_MSC_INTRINSICS) 41#pragma intrinsic(_BitScanReverse) 42 43static INLINE int get_msb(unsigned int n) { 44 unsigned long first_set_bit; 45 assert(n != 0); 46 _BitScanReverse(&first_set_bit, n); 47 return first_set_bit; 48} 49#undef USE_MSC_INTRINSICS 50#else 51// Returns (int)floor(log2(n)). n must be > 0. 52static INLINE int get_msb(unsigned int n) { 53 int log = 0; 54 unsigned int value = n; 55 int i; 56 57 assert(n != 0); 58 59 for (i = 4; i >= 0; --i) { 60 const int shift = (1 << i); 61 const unsigned int x = value >> shift; 62 if (x != 0) { 63 value = x; 64 log += shift; 65 } 66 } 67 return log; 68} 69#endif 70 71#ifdef __cplusplus 72} // extern "C" 73#endif 74 75#endif // VPX_PORTS_BITOPS_H_ 76