103 lines
2.9 KiB
C
103 lines
2.9 KiB
C
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/*
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Simple DirectMedia Layer
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Copyright (C) 1997-2013 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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/* *INDENT-OFF* */
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extern "C" {
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/* *INDENT-ON* */
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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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* Uses inline functions for compilers that support them, and static
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* functions for those that do not. Because these functions become
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* static for compilers that do not support inline functions, this
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* header should only be included in files that actually use them.
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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.
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*/
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static __inline__ Sint8
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SDL_MostSignificantBitIndex32(Uint32 x)
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{
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#if defined(__GNUC__)
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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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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#IntegerLogLookup
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*/
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static const Sint8 LogTable256[256] =
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{
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#define LT(n) n, n, n, n, n, n, n, n, n, n, n, n, n, n, n, n
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-1, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
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LT(4), LT(5), LT(5), LT(6), LT(6), LT(6), LT(6),
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LT(7), LT(7), LT(7), LT(7), LT(7), LT(7), LT(7), LT(7)
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#undef LT
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};
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register unsigned int t, tt;
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if (tt = x >> 16)
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{
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return ((t = tt >> 8) ? 24 + LogTable256[t] : 16 + LogTable256[tt]);
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}
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else
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{
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return ((t = x >> 8) ? 8 + LogTable256[t] : LogTable256[x]);
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}
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#endif
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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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/* *INDENT-OFF* */
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}
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/* *INDENT-ON* */
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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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