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| | | /* |
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| | | Simple DirectMedia Layer |
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| | | Copyright (C) 1997-2014 Sam Lantinga <slouken@libsdl.org> |
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| | | |
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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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| | | |
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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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| | | |
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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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| | | /** |
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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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| | | |
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| | | #ifndef _SDL_bits_h |
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| | | #define _SDL_bits_h |
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| | | |
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| | | #include "SDL_stdinc.h" |
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| | | |
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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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| | | /** |
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| | | * \file SDL_bits.h |
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| | | */ |
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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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| | | 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 |
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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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| | | #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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| | | |
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| | | int msbIndex = 0; |
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| | | int i; |
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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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| | | |
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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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| | | |
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| | | return msbIndex; |
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| | | #endif |
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| | | } |
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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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| | | |
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| | | #endif /* _SDL_bits_h */ |
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| | | |
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| | | /* vi: set ts=4 sw=4 expandtab: */ |
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