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SDL_bits.h
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1 /*
2  Simple DirectMedia Layer
3  Copyright (C) 1997-2018 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 
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 
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
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: */
SDL_FORCE_INLINE int SDL_MostSignificantBitIndex32(Uint32 x)
Definition: SDL_bits.h:61