mirror of
https://github.com/RetroDECK/Duckstation.git
synced 2024-12-04 19:45:41 +00:00
98 lines
2.5 KiB
C
98 lines
2.5 KiB
C
|
/*
|
||
|
|
Simple DirectMedia Layer
|
||
|
|
Copyright (C) 1997-2016 Sam Lantinga <slouken@libsdl.org>
|
||
|
|
|
||
|
|
This software is provided 'as-is', without any express or implied
|
||
|
|
warranty. In no event will the authors be held liable for any damages
|
||
|
|
arising from the use of this software.
|
||
|
|
|
||
|
|
Permission is granted to anyone to use this software for any purpose,
|
||
|
|
including commercial applications, and to alter it and redistribute it
|
||
|
|
freely, subject to the following restrictions:
|
||
|
|
|
||
|
|
1. The origin of this software must not be misrepresented; you must not
|
||
|
|
claim that you wrote the original software. If you use this software
|
||
|
|
in a product, an acknowledgment in the product documentation would be
|
||
|
|
appreciated but is not required.
|
||
|
|
2. Altered source versions must be plainly marked as such, and must not be
|
||
|
|
misrepresented as being the original software.
|
||
|
|
3. This notice may not be removed or altered from any source distribution.
|
||
|
|
*/
|
||
|
|
|
||
|
|
/**
|
||
|
|
* \file SDL_bits.h
|
||
|
|
*
|
||
|
|
* Functions for fiddling with bits and bitmasks.
|
||
|
|
*/
|
||
|
|
|
||
|
|
#ifndef _SDL_bits_h
|
||
|
|
#define _SDL_bits_h
|
||
|
|
|
||
|
|
#include "SDL_stdinc.h"
|
||
|
|
|
||
|
|
#include "begin_code.h"
|
||
|
|
/* Set up for C function definitions, even when using C++ */
|
||
|
|
#ifdef __cplusplus
|
||
|
|
extern "C" {
|
||
|
|
#endif
|
||
|
|
|
||
|
|
/**
|
||
|
|
* \file SDL_bits.h
|
||
|
|
*/
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Get the index of the most significant bit. Result is undefined when called
|
||
|
|
* with 0. This operation can also be stated as "count leading zeroes" and
|
||
|
|
* "log base 2".
|
||
|
|
*
|
||
|
|
* \return Index of the most significant bit, or -1 if the value is 0.
|
||
|
|
*/
|
||
|
|
SDL_FORCE_INLINE int
|
||
|
|
SDL_MostSignificantBitIndex32(Uint32 x)
|
||
|
|
{
|
||
|
|
#if defined(__GNUC__) && __GNUC__ >= 4
|
||
|
|
/* Count Leading Zeroes builtin in GCC.
|
||
|
|
* http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html
|
||
|
|
*/
|
||
|
|
if (x == 0) {
|
||
|
|
return -1;
|
||
|
|
}
|
||
|
|
return 31 - __builtin_clz(x);
|
||
|
|
#else
|
||
|
|
/* Based off of Bit Twiddling Hacks by Sean Eron Anderson
|
||
|
|
* <seander@cs.stanford.edu>, released in the public domain.
|
||
|
|
* http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
|
||
|
|
*/
|
||
|
|
const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
|
||
|
|
const int S[] = {1, 2, 4, 8, 16};
|
||
|
|
|
||
|
|
int msbIndex = 0;
|
||
|
|
int i;
|
||
|
|
|
||
|
|
if (x == 0) {
|
||
|
|
return -1;
|
||
|
|
}
|
||
|
|
|
||
|
|
for (i = 4; i >= 0; i--)
|
||
|
|
{
|
||
|
|
if (x & b[i])
|
||
|
|
{
|
||
|
|
x >>= S[i];
|
||
|
|
msbIndex |= S[i];
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
return msbIndex;
|
||
|
|
#endif
|
||
|
|
}
|
||
|
|
|
||
|
|
/* Ends C function definitions when using C++ */
|
||
|
|
#ifdef __cplusplus
|
||
|
|
}
|
||
|
|
#endif
|
||
|
|
#include "close_code.h"
|
||
|
|
|
||
|
|
#endif /* _SDL_bits_h */
|
||
|
|
|
||
|
|
/* vi: set ts=4 sw=4 expandtab: */
|