1 /*
2 Simple DirectMedia Layer
3 Copyright (C) 1997-2020 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 _inli ne 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
SDL_MostSignificantBitIndex32(Uint32 x)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 SDL_FORCE_INLINE SDL_bool
SDL_HasExactlyOneBitSet32(Uint32 x)105 SDL_HasExactlyOneBitSet32(Uint32 x)
106 {
107 if (x && !(x & (x - 1))) {
108 return SDL_TRUE;
109 }
110 return SDL_FALSE;
111 }
112
113 /* Ends C function definitions when using C++ */
114 #ifdef __cplusplus
115 }
116 #endif
117 #include "close_code.h"
118
119 #endif /* SDL_bits_h_ */
120
121 /* vi: set ts=4 sw=4 expandtab: */
122