kc3-lang/SDL/include/SDL_bits.h

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• Hash : 91a831e2
  Author :
  Date : 2021-01-03T14:02:55
  

  Implement SDL_MostSignificantBitIndex32 using MSVC intrinsics

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• include/SDL_bits.h

• /*
    Simple DirectMedia Layer
    Copyright (C) 1997-2021 Sam Lantinga <slouken@libsdl.org>
  
    This software is provided 'as-is', without any express or implied
    warranty.  In no event will the authors be held liable for any damages
    arising from the use of this software.
  
    Permission is granted to anyone to use this software for any purpose,
    including commercial applications, and to alter it and redistribute it
    freely, subject to the following restrictions:
  
    1. The origin of this software must not be misrepresented; you must not
       claim that you wrote the original software. If you use this software
       in a product, an acknowledgment in the product documentation would be
       appreciated but is not required.
    2. Altered source versions must be plainly marked as such, and must not be
       misrepresented as being the original software.
    3. This notice may not be removed or altered from any source distribution.
  */
  
  /**
   *  \file SDL_bits.h
   *
   *  Functions for fiddling with bits and bitmasks.
   */
  
  #ifndef SDL_bits_h_
  #define SDL_bits_h_
  
  #include "SDL_stdinc.h"
  
  #include "begin_code.h"
  /* Set up for C function definitions, even when using C++ */
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  /**
   *  \file SDL_bits.h
   */
  
  /**
   *  Get the index of the most significant bit. Result is undefined when called
   *  with 0. This operation can also be stated as "count leading zeroes" and
   *  "log base 2".
   *
   *  \return Index of the most significant bit, or -1 if the value is 0.
   */
  #if defined(__WATCOMC__) && defined(__386__)
  extern _inline int _SDL_clz_watcom (Uint32);
  #pragma aux _SDL_clz_watcom = \
      "bsr eax, eax" \
      "xor eax, 31" \
      parm [eax] nomemory \
      value [eax] \
      modify exact [eax] nomemory;
  #endif
  
  SDL_FORCE_INLINE int
  SDL_MostSignificantBitIndex32(Uint32 x)
  {
  #if defined(__GNUC__) && (__GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
      /* Count Leading Zeroes builtin in GCC.
       * http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html
       */
      if (x == 0) {
          return -1;
      }
      return 31 - __builtin_clz(x);
  #elif defined(__WATCOMC__) && defined(__386__)
      if (x == 0) {
          return -1;
      }
      return 31 - _SDL_clz_watcom(x);
  #elif defined(_MSC_VER)
      unsigned long index;
      if (_BitScanReverse(&index, x)) {
          return index;
      }
      return -1;
  #else
      /* Based off of Bit Twiddling Hacks by Sean Eron Anderson
       * <seander@cs.stanford.edu>, released in the public domain.
       * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
       */
      const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
      const int    S[] = {1, 2, 4, 8, 16};
  
      int msbIndex = 0;
      int i;
  
      if (x == 0) {
          return -1;
      }
  
      for (i = 4; i >= 0; i--)
      {
          if (x & b[i])
          {
              x >>= S[i];
              msbIndex |= S[i];
          }
      }
  
      return msbIndex;
  #endif
  }
  
  SDL_FORCE_INLINE SDL_bool
  SDL_HasExactlyOneBitSet32(Uint32 x)
  {
      if (x && !(x & (x - 1))) {
          return SDL_TRUE;
      }
      return SDL_FALSE;
  }
  
  /* Ends C function definitions when using C++ */
  #ifdef __cplusplus
  }
  #endif
  #include "close_code.h"
  
  #endif /* SDL_bits_h_ */
  
  /* vi: set ts=4 sw=4 expandtab: */
  

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