Subversion Repositories Games.Prince of Persia

Rev

Go to most recent revision | Blame | Compare with Previous | Last modification | View Log | Download | RSS feed

  1. /*
  2.   Simple DirectMedia Layer
  3.   Copyright (C) 1997-2017 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 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_clz_watcom (Uint32);
  52. #pragma aux _SDL_clz_watcom = \
  53.     "bsr eax, eax" \
  54.     "xor eax, 31" \
  55.     parm [eax] nomemory \
  56.     value [eax] \
  57.     modify exact [eax] nomemory;
  58. #endif
  59.  
  60. SDL_FORCE_INLINE int
  61. SDL_MostSignificantBitIndex32(Uint32 x)
  62. {
  63. #if defined(__GNUC__) && (__GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
  64.     /* Count Leading Zeroes builtin in GCC.
  65.      * http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html
  66.      */
  67.     if (x == 0) {
  68.         return -1;
  69.     }
  70.     return 31 - __builtin_clz(x);
  71. #elif defined(__WATCOMC__) && defined(__386__)
  72.     if (x == 0) {
  73.         return -1;
  74.     }
  75.     return 31 - _SDL_clz_watcom(x);
  76. #else
  77.     /* Based off of Bit Twiddling Hacks by Sean Eron Anderson
  78.      * <seander@cs.stanford.edu>, released in the public domain.
  79.      * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
  80.      */
  81.     const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
  82.     const int    S[] = {1, 2, 4, 8, 16};
  83.  
  84.     int msbIndex = 0;
  85.     int i;
  86.  
  87.     if (x == 0) {
  88.         return -1;
  89.     }
  90.  
  91.     for (i = 4; i >= 0; i--)
  92.     {
  93.         if (x & b[i])
  94.         {
  95.             x >>= S[i];
  96.             msbIndex |= S[i];
  97.         }
  98.     }
  99.  
  100.     return msbIndex;
  101. #endif
  102. }
  103.  
  104. /* Ends C function definitions when using C++ */
  105. #ifdef __cplusplus
  106. }
  107. #endif
  108. #include "close_code.h"
  109.  
  110. #endif /* SDL_bits_h_ */
  111.  
  112. /* vi: set ts=4 sw=4 expandtab: */
  113.