Rev 1 | Details | Compare with Previous | Last modification | View Log | RSS feed
| Rev | Author | Line No. | Line |
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| 1 | pmbaty | 1 | /* |
| 2 | Simple DirectMedia Layer |
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| 8 | pmbaty | 3 | Copyright (C) 1997-2018 Sam Lantinga <slouken@libsdl.org> |
| 1 | pmbaty | 4 | |
| 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 | |||
| 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 | |||
| 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 | |||
| 22 | /** |
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| 23 | * \file SDL_bits.h |
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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 | |||
| 28 | #ifndef SDL_bits_h_ |
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| 29 | #define SDL_bits_h_ |
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| 30 | |||
| 31 | #include "SDL_stdinc.h" |
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| 32 | |||
| 33 | #include "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 | |||
| 39 | /** |
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| 40 | * \file SDL_bits.h |
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| 41 | */ |
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| 42 | |||
| 43 | /** |
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| 44 | * Get the index of the most significant bit. Result is undefined when called |
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| 45 | * with 0. This operation can also be stated as "count leading zeroes" and |
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| 46 | * "log base 2". |
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| 47 | * |
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| 48 | * \return Index of the most significant bit, or -1 if the value is 0. |
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| 49 | */ |
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| 50 | #if defined(__WATCOMC__) && defined(__386__) |
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| 51 | extern _inline int _SDL_clz_watcom (Uint32); |
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| 52 | #pragma aux _SDL_clz_watcom = \ |
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| 53 | "bsr eax, eax" \ |
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| 54 | "xor eax, 31" \ |
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| 55 | parm [eax] nomemory \ |
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| 56 | value [eax] \ |
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| 57 | modify exact [eax] nomemory; |
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| 58 | #endif |
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| 59 | |||
| 60 | SDL_FORCE_INLINE int |
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| 61 | SDL_MostSignificantBitIndex32(Uint32 x) |
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| 62 | { |
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| 63 | #if defined(__GNUC__) && (__GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)) |
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| 64 | /* Count Leading Zeroes builtin in GCC. |
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| 65 | * http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html |
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| 66 | */ |
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| 67 | if (x == 0) { |
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| 68 | return -1; |
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| 69 | } |
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| 70 | return 31 - __builtin_clz(x); |
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| 71 | #elif defined(__WATCOMC__) && defined(__386__) |
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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 - _SDL_clz_watcom(x); |
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| 76 | #else |
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| 77 | /* Based off of Bit Twiddling Hacks by Sean Eron Anderson |
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| 78 | * <seander@cs.stanford.edu>, released in the public domain. |
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| 79 | * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog |
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| 80 | */ |
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| 81 | const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000}; |
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| 82 | const int S[] = {1, 2, 4, 8, 16}; |
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| 83 | |||
| 84 | int msbIndex = 0; |
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| 85 | int i; |
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| 86 | |||
| 87 | if (x == 0) { |
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| 88 | return -1; |
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| 89 | } |
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| 90 | |||
| 91 | for (i = 4; i >= 0; i--) |
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| 92 | { |
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| 93 | if (x & b[i]) |
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| 94 | { |
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| 95 | x >>= S[i]; |
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| 96 | msbIndex |= S[i]; |
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| 97 | } |
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| 98 | } |
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| 99 | |||
| 100 | return msbIndex; |
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| 101 | #endif |
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| 102 | } |
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| 103 | |||
| 104 | /* Ends C function definitions when using C++ */ |
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| 105 | #ifdef __cplusplus |
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| 106 | } |
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| 107 | #endif |
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| 108 | #include "close_code.h" |
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| 109 | |||
| 110 | #endif /* SDL_bits_h_ */ |
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| 111 | |||
| 112 | /* vi: set ts=4 sw=4 expandtab: */ |