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148 lines
4.3 KiB
C
148 lines
4.3 KiB
C
/*
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Simple DirectMedia Layer
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Copyright (C) 1997-2024 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 <SDL3/SDL_stdinc.h>
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#include <SDL3/SDL_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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#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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* Get the index of the most significant (set) bit in a 32-bit number.
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*
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* Result is undefined when called with 0. This operation can also be stated
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* as "count leading zeroes" and "log base 2".
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*
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* Note that this is a forced-inline function in a header, and not a public
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* API function available in the SDL library (which is to say, the code is
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* embedded in the calling program and the linker and dynamic loader will not
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* be able to find this function inside SDL itself).
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*
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* \param x the 32-bit value to examine.
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* \returns the index of the most significant bit, or -1 if the value is 0.
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*
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* \threadsafety It is safe to call this function from any thread.
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*
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* \since This function is available since SDL 3.1.3.
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*/
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SDL_FORCE_INLINE int 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 (int)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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/**
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* Determine if a unsigned 32-bit value has exactly one bit set.
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*
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* If there are no bits set (`x` is zero), or more than one bit set, this
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* returns false. If any one bit is exclusively set, this returns true.
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*
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* Note that this is a forced-inline function in a header, and not a public
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* API function available in the SDL library (which is to say, the code is
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* embedded in the calling program and the linker and dynamic loader will not
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* be able to find this function inside SDL itself).
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*
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* \param x the 32-bit value to examine.
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* \returns true if exactly one bit is set in `x`, false otherwise.
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*
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* \threadsafety It is safe to call this function from any thread.
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*
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* \since This function is available since SDL 3.1.3.
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*/
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SDL_FORCE_INLINE bool SDL_HasExactlyOneBitSet32(Uint32 x)
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{
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if (x && !(x & (x - 1))) {
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return true;
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}
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return 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 <SDL3/SDL_close_code.h>
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#endif /* SDL_bits_h_ */
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