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121 lines
3.0 KiB
121 lines
3.0 KiB
/* |
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Simple DirectMedia Layer |
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Copyright (C) 1997-2020 Sam Lantinga <slouken@libsdl.org> |
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This software is provided 'as-is', without any express or implied |
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warranty. In no event will the authors be held liable for any damages |
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arising from the use of this software. |
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Permission is granted to anyone to use this software for any purpose, |
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including commercial applications, and to alter it and redistribute it |
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freely, subject to the following restrictions: |
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1. The origin of this software must not be misrepresented; you must not |
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claim that you wrote the original software. If you use this software |
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in a product, an acknowledgment in the product documentation would be |
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appreciated but is not required. |
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2. Altered source versions must be plainly marked as such, and must not be |
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misrepresented as being the original software. |
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3. This notice may not be removed or altered from any source distribution. |
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*/ |
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/** |
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* \file SDL_bits.h |
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* |
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* Functions for fiddling with bits and bitmasks. |
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*/ |
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#ifndef SDL_bits_h_ |
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#define SDL_bits_h_ |
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#include "SDL_stdinc.h" |
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#include "begin_code.h" |
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/* Set up for C function definitions, even when using C++ */ |
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#ifdef __cplusplus |
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extern "C" { |
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#endif |
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/** |
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* \file SDL_bits.h |
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*/ |
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/** |
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* Get the index of the most significant bit. Result is undefined when called |
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* with 0. This operation can also be stated as "count leading zeroes" and |
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* "log base 2". |
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* |
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* \return Index of the most significant bit, or -1 if the value is 0. |
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*/ |
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#if defined(__WATCOMC__) && defined(__386__) |
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extern _inline int _SDL_clz_watcom (Uint32); |
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#pragma aux _SDL_clz_watcom = \ |
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"bsr eax, eax" \ |
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"xor eax, 31" \ |
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parm [eax] nomemory \ |
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value [eax] \ |
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modify exact [eax] nomemory; |
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#endif |
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SDL_FORCE_INLINE int |
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SDL_MostSignificantBitIndex32(Uint32 x) |
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{ |
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#if defined(__GNUC__) && (__GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)) |
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/* Count Leading Zeroes builtin in GCC. |
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* http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html |
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*/ |
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if (x == 0) { |
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return -1; |
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} |
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return 31 - __builtin_clz(x); |
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#elif defined(__WATCOMC__) && defined(__386__) |
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if (x == 0) { |
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return -1; |
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} |
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return 31 - _SDL_clz_watcom(x); |
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#else |
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/* Based off of Bit Twiddling Hacks by Sean Eron Anderson |
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* <seander@cs.stanford.edu>, released in the public domain. |
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* http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog |
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*/ |
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const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000}; |
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const int S[] = {1, 2, 4, 8, 16}; |
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int msbIndex = 0; |
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int i; |
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if (x == 0) { |
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return -1; |
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} |
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for (i = 4; i >= 0; i--) |
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{ |
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if (x & b[i]) |
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{ |
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x >>= S[i]; |
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msbIndex |= S[i]; |
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} |
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} |
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return msbIndex; |
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#endif |
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} |
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SDL_FORCE_INLINE SDL_bool |
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SDL_HasExactlyOneBitSet32(Uint32 x) |
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{ |
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if (x && !(x & (x - 1))) { |
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return SDL_TRUE; |
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} |
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return SDL_FALSE; |
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} |
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/* Ends C function definitions when using C++ */ |
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#ifdef __cplusplus |
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} |
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#endif |
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#include "close_code.h" |
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#endif /* SDL_bits_h_ */ |
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/* vi: set ts=4 sw=4 expandtab: */
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