1/*
2 Simple DirectMedia Layer
3 Copyright (C) 1997-2021 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
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 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
59SDL_FORCE_INLINE int
60SDL_MostSignificantBitIndex32(Uint32 x)
61{
62#if defined(__GNUC__) && (__GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
63 /* Count Leading Zeroes builtin in GCC.
64 * http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html
65 */
66 if (x == 0) {
67 return -1;
68 }
69 return 31 - __builtin_clz(x);
70#elif defined(__WATCOMC__) && defined(__386__)
71 if (x == 0) {
72 return -1;
73 }
74 return _SDL_bsr_watcom(x);
75#elif defined(_MSC_VER)
76 unsigned long index;
77 if (_BitScanReverse(&index, x)) {
78 return index;
79 }
80 return -1;
81#else
82 /* Based off of Bit Twiddling Hacks by Sean Eron Anderson
83 * <seander@cs.stanford.edu>, released in the public domain.
84 * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
85 */
86 const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
87 const int S[] = {1, 2, 4, 8, 16};
88
89 int msbIndex = 0;
90 int i;
91
92 if (x == 0) {
93 return -1;
94 }
95
96 for (i = 4; i >= 0; i--)
97 {
98 if (x & b[i])
99 {
100 x >>= S[i];
101 msbIndex |= S[i];
102 }
103 }
104
105 return msbIndex;
106#endif
107}
108
109SDL_FORCE_INLINE SDL_bool
110SDL_HasExactlyOneBitSet32(Uint32 x)
111{
112 if (x && !(x & (x - 1))) {
113 return SDL_TRUE;
114 }
115 return SDL_FALSE;
116}
117
118/* Ends C function definitions when using C++ */
119#ifdef __cplusplus
120}
121#endif
122#include "close_code.h"
123
124#endif /* SDL_bits_h_ */
125
126/* vi: set ts=4 sw=4 expandtab: */
127