SDL 2.0
SDL_bits.h
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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
36extern "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__)
51extern __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 */
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 return -1;
74 }
75 return 31 - __builtin_clz(x);
76#elif defined(__WATCOMC__) && defined(__386__)
77 if (x == 0) {
78 return -1;
79 }
80 return _SDL_bsr_watcom(x);
81#elif defined(_MSC_VER)
82 unsigned long index;
83 if (_BitScanReverse(&index, x)) {
84 return index;
85 }
86 return -1;
87#else
88 /* Based off of Bit Twiddling Hacks by Sean Eron Anderson
89 * <seander@cs.stanford.edu>, released in the public domain.
90 * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
91 */
92 const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
93 const int S[] = {1, 2, 4, 8, 16};
94
95 int msbIndex = 0;
96 int i;
97
98 if (x == 0) {
99 return -1;
100 }
101
102 for (i = 4; i >= 0; i--)
103 {
104 if (x & b[i])
105 {
106 x >>= S[i];
107 msbIndex |= S[i];
108 }
109 }
110
111 return msbIndex;
112#endif
113}
114
117{
118 if (x && !(x & (x - 1))) {
119 return SDL_TRUE;
120 }
121 return SDL_FALSE;
122}
123
124/* Ends C function definitions when using C++ */
125#ifdef __cplusplus
126}
127#endif
128#include "close_code.h"
129
130#endif /* SDL_bits_h_ */
131
132/* vi: set ts=4 sw=4 expandtab: */
SDL_FORCE_INLINE SDL_bool SDL_HasExactlyOneBitSet32(Uint32 x)
Definition SDL_bits.h:116
SDL_FORCE_INLINE int SDL_MostSignificantBitIndex32(Uint32 x)
Definition SDL_bits.h:66
SDL_bool
Definition SDL_stdinc.h:187
@ SDL_TRUE
Definition SDL_stdinc.h:189
@ SDL_FALSE
Definition SDL_stdinc.h:188
uint32_t Uint32
Definition SDL_stdinc.h:231
#define SDL_FORCE_INLINE
Definition begin_code.h:145