1 /*
2 Simple DirectMedia Layer
3 Copyright (C) 1997-2025 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 * # CategoryBits
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 /**
60 * Use this function to get the index of the most significant (set) bit in a
61 *
62 * \param x the number to find the MSB of.
63 * \returns the index of the most significant bit of x, or -1 if x is 0.
64 */
65 SDL_FORCE_INLINE int
SDL_MostSignificantBitIndex32(Uint32 x)66 SDL_MostSignificantBitIndex32(Uint32 x)
67 {
68 #if defined(__GNUC__) && (__GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
69 /* Count Leading Zeroes builtin in GCC.
70 * http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html
71 */
72 if (x == 0)
73 {
74 return -1;
75 }
76 return 31 - __builtin_clz(x);
77 #elif defined(__WATCOMC__) && defined(__386__)
78 if (x == 0)
79 {
80 return -1;
81 }
82 return _SDL_bsr_watcom(x);
83 #elif defined(_MSC_VER)
84 unsigned long index;
85 if (_BitScanReverse(&index, x))
86 {
87 return index;
88 }
89 return -1;
90 #else
91 /* Based off of Bit Twiddling Hacks by Sean Eron Anderson
92 * <seander@cs.stanford.edu>, released in the public domain.
93 * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
94 */
95 const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
96 const int S[] = {1, 2, 4, 8, 16};
97
98 int msbIndex = 0;
99 int i;
100
101 if (x == 0)
102 {
103 return -1;
104 }
105
106 for (i = 4; i >= 0; i--)
107 {
108 if (x & b[i])
109 {
110 x >>= S[i];
111 msbIndex |= S[i];
112 }
113 }
114
115 return msbIndex;
116 #endif
117 }
118
119 SDL_FORCE_INLINE SDL_bool
SDL_HasExactlyOneBitSet32(Uint32 x)120 SDL_HasExactlyOneBitSet32(Uint32 x)
121 {
122 if (x && !(x & (x - 1)))
123 {
124 return SDL_TRUE;
125 }
126 return SDL_FALSE;
127 }
128
129 /* Ends C function definitions when using C++ */
130 #ifdef __cplusplus
131 }
132 #endif
133 #include "close_code.h"
134
135 #endif /* SDL_bits_h_ */
136
137 /* vi: set ts=4 sw=4 expandtab: */