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 26 extern "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) 36 static 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 43 static 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. 52 static 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
