1 /* 2 * Copyright (c) 2016, Alliance for Open Media. All rights reserved 3 * 4 * This source code is subject to the terms of the BSD 2 Clause License and 5 * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License 6 * was not distributed with this source code in the LICENSE file, you can 7 * obtain it at www.aomedia.org/license/software. If the Alliance for Open 8 * Media Patent License 1.0 was not distributed with this source code in the 9 * PATENTS file, you can obtain it at www.aomedia.org/license/patent. 10 */ 11 12 #ifndef AOM_PORTS_BITOPS_H_ 13 #define AOM_PORTS_BITOPS_H_ 14 15 #include <assert.h> 16 17 #include "aom_ports/msvc.h" 18 19 #ifdef _MSC_VER 20 #if defined(_M_X64) || defined(_M_IX86) 21 #include <intrin.h> 22 #define USE_MSC_INTRINSICS 23 #endif 24 #endif 25 26 #ifdef __cplusplus 27 extern "C" { 28 #endif 29 30 // These versions of get_msb() are only valid when n != 0 because all 31 // of the optimized versions are undefined when n == 0: 32 // https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html 33 34 // use GNU builtins where available. 35 #if defined(__GNUC__) && \ 36 ((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4) get_msb(unsigned int n)37static INLINE int get_msb(unsigned int n) { 38 assert(n != 0); 39 return 31 ^ __builtin_clz(n); 40 } 41 #elif defined(USE_MSC_INTRINSICS) 42 #pragma intrinsic(_BitScanReverse) 43 44 static INLINE int get_msb(unsigned int n) { 45 unsigned long first_set_bit; 46 assert(n != 0); 47 _BitScanReverse(&first_set_bit, n); 48 return first_set_bit; 49 } 50 #undef USE_MSC_INTRINSICS 51 #else 52 // Returns (int)floor(log2(n)). n must be > 0. 53 static INLINE int get_msb(unsigned int n) { 54 int log = 0; 55 unsigned int value = n; 56 int i; 57 58 assert(n != 0); 59 60 for (i = 4; i >= 0; --i) { 61 const int shift = (1 << i); 62 const unsigned int x = value >> shift; 63 if (x != 0) { 64 value = x; 65 log += shift; 66 } 67 } 68 return log; 69 } 70 #endif 71 72 #ifdef __cplusplus 73 } // extern "C" 74 #endif 75 76 #endif // AOM_PORTS_BITOPS_H_ 77