Line data    Source code

       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)
      37           0 : static INLINE int get_msb(unsigned int n) {
      38           0 :   assert(n != 0);
      39           0 :   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_