Line data    Source code

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