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  1. /*
  2.   Simple DirectMedia Layer
  3.   Copyright (C) 1997-2023 Sam Lantinga <slouken@libsdl.org>
  4.  
  5.   This software is provided 'as-is', without any express or implied
  6.   warranty.  In no event will the authors be held liable for any damages
  7.   arising from the use of this software.
  8.  
  9.   Permission is granted to anyone to use this software for any purpose,
  10.   including commercial applications, and to alter it and redistribute it
  11.   freely, subject to the following restrictions:
  12.  
  13.   1. The origin of this software must not be misrepresented; you must not
  14.      claim that you wrote the original software. If you use this software
  15.      in a product, an acknowledgment in the product documentation would be
  16.      appreciated but is not required.
  17.   2. Altered source versions must be plainly marked as such, and must not be
  18.      misrepresented as being the original software.
  19.   3. This notice may not be removed or altered from any source distribution.
  20. */
  21.  
  22. /**
  23.  *  \file SDL_bits.h
  24.  *
  25.  *  Functions for fiddling with bits and bitmasks.
  26.  */
  27.  
  28. #ifndef SDL_bits_h_
  29. #define SDL_bits_h_
  30.  
  31. #include "SDL_stdinc.h"
  32.  
  33. #include "begin_code.h"
  34. /* Set up for C function definitions, even when using C++ */
  35. #ifdef __cplusplus
  36. extern "C" {
  37. #endif
  38.  
  39. /**
  40.  *  \file SDL_bits.h
  41.  */
  42.  
  43. /**
  44.  *  Get the index of the most significant bit. Result is undefined when called
  45.  *  with 0. This operation can also be stated as "count leading zeroes" and
  46.  *  "log base 2".
  47.  *
  48.  *  \return the index of the most significant bit, or -1 if the value is 0.
  49.  */
  50. #if defined(__WATCOMC__) && defined(__386__)
  51. extern __inline int _SDL_bsr_watcom(Uint32);
  52. #pragma aux _SDL_bsr_watcom = \
  53.     "bsr eax, eax" \
  54.     parm [eax] nomemory \
  55.     value [eax] \
  56.     modify exact [eax] nomemory;
  57. #endif
  58.  
  59. SDL_FORCE_INLINE int
  60. SDL_MostSignificantBitIndex32(Uint32 x)
  61. {
  62. #if defined(__GNUC__) && (__GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
  63.     /* Count Leading Zeroes builtin in GCC.
  64.      * http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html
  65.      */
  66.     if (x == 0) {
  67.         return -1;
  68.     }
  69.     return 31 - __builtin_clz(x);
  70. #elif defined(__WATCOMC__) && defined(__386__)
  71.     if (x == 0) {
  72.         return -1;
  73.     }
  74.     return _SDL_bsr_watcom(x);
  75. #elif defined(_MSC_VER)
  76.     unsigned long index;
  77.     if (_BitScanReverse(&index, x)) {
  78.         return index;
  79.     }
  80.     return -1;
  81. #else
  82.     /* Based off of Bit Twiddling Hacks by Sean Eron Anderson
  83.      * <seander@cs.stanford.edu>, released in the public domain.
  84.      * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
  85.      */
  86.     const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
  87.     const int    S[] = {1, 2, 4, 8, 16};
  88.  
  89.     int msbIndex = 0;
  90.     int i;
  91.  
  92.     if (x == 0) {
  93.         return -1;
  94.     }
  95.  
  96.     for (i = 4; i >= 0; i--)
  97.     {
  98.         if (x & b[i])
  99.         {
  100.             x >>= S[i];
  101.             msbIndex |= S[i];
  102.         }
  103.     }
  104.  
  105.     return msbIndex;
  106. #endif
  107. }
  108.  
  109. SDL_FORCE_INLINE SDL_bool
  110. SDL_HasExactlyOneBitSet32(Uint32 x)
  111. {
  112.     if (x && !(x & (x - 1))) {
  113.         return SDL_TRUE;
  114.     }
  115.     return SDL_FALSE;
  116. }
  117.  
  118. /* Ends C function definitions when using C++ */
  119. #ifdef __cplusplus
  120. }
  121. #endif
  122. #include "close_code.h"
  123.  
  124. #endif /* SDL_bits_h_ */
  125.  
  126. /* vi: set ts=4 sw=4 expandtab: */
  127.