SDL
2.0
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) 1997-2025 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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* # CategoryBits
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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 the 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_bsr_watcom(
Uint32
);
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#pragma aux _SDL_bsr_watcom = \
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"bsr eax, eax" \
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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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/**
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* Use this function to get the index of the most significant (set) bit in a
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*
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* \param x the number to find the MSB of.
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* \returns the index of the most significant bit of x, or -1 if x 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 || (__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
_SDL_bsr_watcom(x);
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#elif defined(_MSC_VER)
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unsigned
long
index;
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if
(_BitScanReverse(&index, x)) {
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return
index;
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}
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return
-1;
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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: */
SDL_HasExactlyOneBitSet32
SDL_FORCE_INLINE SDL_bool SDL_HasExactlyOneBitSet32(Uint32 x)
Definition
SDL_bits.h:116
SDL_MostSignificantBitIndex32
SDL_FORCE_INLINE int SDL_MostSignificantBitIndex32(Uint32 x)
Definition
SDL_bits.h:66
SDL_stdinc.h
SDL_bool
SDL_bool
Definition
SDL_stdinc.h:187
SDL_TRUE
@ SDL_TRUE
Definition
SDL_stdinc.h:189
SDL_FALSE
@ SDL_FALSE
Definition
SDL_stdinc.h:188
Uint32
uint32_t Uint32
Definition
SDL_stdinc.h:231
begin_code.h
SDL_FORCE_INLINE
#define SDL_FORCE_INLINE
Definition
begin_code.h:145
close_code.h
include
SDL_bits.h
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