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1
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1 /*
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2 Simple DirectMedia Layer
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3 Copyright (C) 1997-2025 Sam Lantinga <slouken@libsdl.org>
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4
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5 This software is provided 'as-is', without any express or implied
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6 warranty. In no event will the authors be held liable for any damages
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7 arising from the use of this software.
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8
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9 Permission is granted to anyone to use this software for any purpose,
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10 including commercial applications, and to alter it and redistribute it
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11 freely, subject to the following restrictions:
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12
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13 1. The origin of this software must not be misrepresented; you must not
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14 claim that you wrote the original software. If you use this software
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15 in a product, an acknowledgment in the product documentation would be
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16 appreciated but is not required.
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17 2. Altered source versions must be plainly marked as such, and must not be
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18 misrepresented as being the original software.
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19 3. This notice may not be removed or altered from any source distribution.
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20 */
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21
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22 /**
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23 * # CategoryBits
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24 *
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25 * Functions for fiddling with bits and bitmasks.
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26 */
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27
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28 #ifndef SDL_bits_h_
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29 #define SDL_bits_h_
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30
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31 #include <SDL3/SDL_stdinc.h>
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32
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33 #include <SDL3/SDL_begin_code.h>
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34 /* Set up for C function definitions, even when using C++ */
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35 #ifdef __cplusplus
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36 extern "C" {
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37 #endif
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38
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39 #if defined(__WATCOMC__) && defined(__386__)
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40 extern __inline int _SDL_bsr_watcom(Uint32);
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41 #pragma aux _SDL_bsr_watcom = \
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42 "bsr eax, eax" \
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43 parm [eax] nomemory \
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44 value [eax] \
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45 modify exact [eax] nomemory;
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46 #endif
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47
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48 /**
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49 * Get the index of the most significant (set) bit in a 32-bit number.
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50 *
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51 * Result is undefined when called with 0. This operation can also be stated
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52 * as "count leading zeroes" and "log base 2".
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53 *
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54 * Note that this is a forced-inline function in a header, and not a public
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55 * API function available in the SDL library (which is to say, the code is
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56 * embedded in the calling program and the linker and dynamic loader will not
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57 * be able to find this function inside SDL itself).
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58 *
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59 * \param x the 32-bit value to examine.
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60 * \returns the index of the most significant bit, or -1 if the value is 0.
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61 *
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62 * \threadsafety It is safe to call this function from any thread.
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63 *
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64 * \since This function is available since SDL 3.2.0.
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65 */
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66 SDL_FORCE_INLINE int SDL_MostSignificantBitIndex32(Uint32 x)
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67 {
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68 #if defined(__GNUC__) && (__GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
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69 /* Count Leading Zeroes builtin in GCC.
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70 * http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html
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71 */
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72 if (x == 0) {
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73 return -1;
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74 }
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75 return 31 - __builtin_clz(x);
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76 #elif defined(__WATCOMC__) && defined(__386__)
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77 if (x == 0) {
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78 return -1;
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79 }
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80 return _SDL_bsr_watcom(x);
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81 #elif defined(_MSC_VER) && _MSC_VER >= 1400
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82 unsigned long index;
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83 if (_BitScanReverse(&index, x)) {
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84 return (int)index;
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85 }
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86 return -1;
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87 #else
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88 /* Based off of Bit Twiddling Hacks by Sean Eron Anderson
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89 * <seander@cs.stanford.edu>, released in the public domain.
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90 * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
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91 */
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92 const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
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93 const int S[] = {1, 2, 4, 8, 16};
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94
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95 int msbIndex = 0;
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96 int i;
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97
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98 if (x == 0) {
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99 return -1;
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100 }
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101
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102 for (i = 4; i >= 0; i--)
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103 {
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104 if (x & b[i])
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105 {
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106 x >>= S[i];
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107 msbIndex |= S[i];
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108 }
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109 }
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110
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111 return msbIndex;
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112 #endif
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113 }
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114
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115 /**
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116 * Determine if a unsigned 32-bit value has exactly one bit set.
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117 *
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118 * If there are no bits set (`x` is zero), or more than one bit set, this
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119 * returns false. If any one bit is exclusively set, this returns true.
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120 *
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121 * Note that this is a forced-inline function in a header, and not a public
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122 * API function available in the SDL library (which is to say, the code is
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123 * embedded in the calling program and the linker and dynamic loader will not
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124 * be able to find this function inside SDL itself).
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125 *
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126 * \param x the 32-bit value to examine.
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127 * \returns true if exactly one bit is set in `x`, false otherwise.
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128 *
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129 * \threadsafety It is safe to call this function from any thread.
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130 *
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131 * \since This function is available since SDL 3.2.0.
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132 */
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133 SDL_FORCE_INLINE bool SDL_HasExactlyOneBitSet32(Uint32 x)
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134 {
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135 if (x && !(x & (x - 1))) {
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136 return true;
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137 }
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138 return false;
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139 }
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140
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141 /* Ends C function definitions when using C++ */
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142 #ifdef __cplusplus
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143 }
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144 #endif
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145 #include <SDL3/SDL_close_code.h>
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146
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147 #endif /* SDL_bits_h_ */
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