| /* |
| * Copyright (c) 2016, Alliance for Open Media. All rights reserved |
| * |
| * This source code is subject to the terms of the BSD 2 Clause License and |
| * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License |
| * was not distributed with this source code in the LICENSE file, you can |
| * obtain it at www.aomedia.org/license/software. If the Alliance for Open |
| * Media Patent License 1.0 was not distributed with this source code in the |
| * PATENTS file, you can obtain it at www.aomedia.org/license/patent. |
| */ |
| |
| #ifndef AOM_AOM_PORTS_BITOPS_H_ |
| #define AOM_AOM_PORTS_BITOPS_H_ |
| |
| #include <assert.h> |
| |
| #include "aom_ports/msvc.h" |
| #include "config/aom_config.h" |
| |
| #ifdef _MSC_VER |
| #if defined(_M_X64) || defined(_M_IX86) |
| #include <intrin.h> |
| #define USE_MSC_INTRINSICS |
| #endif |
| #endif |
| |
| #ifdef __cplusplus |
| extern "C" { |
| #endif |
| |
| // get_msb: |
| // Returns (int)floor(log2(n)). n must be > 0. |
| // These versions of get_msb() are only valid when n != 0 because all |
| // of the optimized versions are undefined when n == 0: |
| // https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html |
| |
| // use GNU builtins where available. |
| #if defined(__GNUC__) && \ |
| ((__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || __GNUC__ >= 4) |
| static INLINE int get_msb(unsigned int n) { |
| assert(n != 0); |
| return 31 ^ __builtin_clz(n); |
| } |
| #elif defined(USE_MSC_INTRINSICS) |
| #pragma intrinsic(_BitScanReverse) |
| |
| static INLINE int get_msb(unsigned int n) { |
| unsigned long first_set_bit; |
| assert(n != 0); |
| _BitScanReverse(&first_set_bit, n); |
| return first_set_bit; |
| } |
| #undef USE_MSC_INTRINSICS |
| #else |
| static INLINE int get_msb(unsigned int n) { |
| int log = 0; |
| unsigned int value = n; |
| int i; |
| |
| assert(n != 0); |
| |
| for (i = 4; i >= 0; --i) { |
| const int shift = (1 << i); |
| const unsigned int x = value >> shift; |
| if (x != 0) { |
| value = x; |
| log += shift; |
| } |
| } |
| return log; |
| } |
| #endif |
| |
| #ifdef __cplusplus |
| } // extern "C" |
| #endif |
| |
| #endif // AOM_AOM_PORTS_BITOPS_H_ |