| /* |
| * Copyright (c) 2010 The WebM project authors. All Rights Reserved. |
| * |
| * Use of this source code is governed by a BSD-style license |
| * that can be found in the LICENSE file in the root of the source |
| * tree. An additional intellectual property rights grant can be found |
| * in the file PATENTS. All contributing project authors may |
| * be found in the AUTHORS file in the root of the source tree. |
| */ |
| |
| #ifndef VPX_VPX_PORTS_BITOPS_H_ |
| #define VPX_VPX_PORTS_BITOPS_H_ |
| |
| #include <assert.h> |
| |
| #include "vpx_ports/msvc.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 |
| |
| // These versions of get_lsb() and 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_lsb(unsigned int n) { |
| assert(n != 0); |
| return __builtin_ctz(n); |
| } |
| |
| static INLINE int get_msb(unsigned int n) { |
| assert(n != 0); |
| return 31 ^ __builtin_clz(n); |
| } |
| #elif defined(USE_MSC_INTRINSICS) |
| #pragma intrinsic(_BitScanForward) |
| #pragma intrinsic(_BitScanReverse) |
| |
| static INLINE int get_lsb(unsigned int n) { |
| unsigned long first_set_bit; // NOLINT(runtime/int) |
| _BitScanForward(&first_set_bit, n); |
| return first_set_bit; |
| } |
| |
| 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_lsb(unsigned int n) { |
| int i; |
| assert(n != 0); |
| for (i = 0; i < 32 && !(n & 1); ++i) n >>= 1; |
| return i; |
| } |
| |
| // Returns (int)floor(log2(n)). n must be > 0. |
| 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 // VPX_VPX_PORTS_BITOPS_H_ |