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SDL_bits.h
Go to the documentation of this file.
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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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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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#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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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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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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/* 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: */
begin_code.h
SDL_stdinc.h
close_code.h
SDL_MostSignificantBitIndex32
SDL_FORCE_INLINE int SDL_MostSignificantBitIndex32(Uint32 x)
Definition:
SDL_bits.h:51
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