jorgen@6866: /*
jorgen@6866:   Simple DirectMedia Layer
jorgen@6866:   Copyright (C) 1997-2013 Sam Lantinga <slouken@libsdl.org>
jorgen@6866: 
jorgen@6866:   This software is provided 'as-is', without any express or implied
jorgen@6866:   warranty.  In no event will the authors be held liable for any damages
jorgen@6866:   arising from the use of this software.
jorgen@6866: 
jorgen@6866:   Permission is granted to anyone to use this software for any purpose,
jorgen@6866:   including commercial applications, and to alter it and redistribute it
jorgen@6866:   freely, subject to the following restrictions:
jorgen@6866: 
jorgen@6866:   1. The origin of this software must not be misrepresented; you must not
jorgen@6866:      claim that you wrote the original software. If you use this software
jorgen@6866:      in a product, an acknowledgment in the product documentation would be
jorgen@6866:      appreciated but is not required.
jorgen@6866:   2. Altered source versions must be plainly marked as such, and must not be
jorgen@6866:      misrepresented as being the original software.
jorgen@6866:   3. This notice may not be removed or altered from any source distribution.
jorgen@6866: */
jorgen@6866: 
jorgen@6866: /**
jorgen@6866:  *  \file SDL_bits.h
jorgen@6866:  *
jorgen@6866:  *  Functions for fiddling with bits and bitmasks.
jorgen@6866:  */
jorgen@6866: 
jorgen@6866: #ifndef _SDL_bits_h
jorgen@6866: #define _SDL_bits_h
jorgen@6866: 
jorgen@6866: #include "SDL_stdinc.h"
jorgen@6866: 
jorgen@6866: #include "begin_code.h"
jorgen@6866: /* Set up for C function definitions, even when using C++ */
jorgen@6866: #ifdef __cplusplus
jorgen@6866: /* *INDENT-OFF* */
jorgen@6866: extern "C" {
jorgen@6866: /* *INDENT-ON* */
jorgen@6866: #endif
jorgen@6866: 
jorgen@6866: /**
jorgen@6866:  *  \file SDL_bits.h
jorgen@6866:  */
jorgen@6866: 
jorgen@6866: /**
jorgen@6866:  *  Get the index of the most significant bit. Result is undefined when called
jorgen@6866:  *  with 0. This operation can also be stated as "count leading zeroes" and
jorgen@6866:  *  "log base 2".
jorgen@6866:  *
jorgen@6866:  *  \return Index of the most significant bit.
jorgen@6866:  */
icculus@7004: SDL_FORCE_INLINE Sint8
jorgen@6866: SDL_MostSignificantBitIndex32(Uint32 x)
jorgen@6866: {
icculus@7033: #if defined(__GNUC__) && __GNUC__ >= 4
jorgen@6866:     /* Count Leading Zeroes builtin in GCC.
jorgen@6866:      * http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html
jorgen@6866:      */
jorgen@6866:     return 31 - __builtin_clz(x);
jorgen@6866: #else
jorgen@6866:     /* Based off of Bit Twiddling Hacks by Sean Eron Anderson
jorgen@6866:      * <seander@cs.stanford.edu>, released in the public domain.
jorgen@6873:      * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
jorgen@6866:      */
jorgen@6873:     const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
jorgen@6873:     const Uint8  S[] = {1, 2, 4, 8, 16};
jorgen@6873: 
jorgen@6873:     Uint8 msbIndex = 0;
jorgen@6873:     int i;
jorgen@6873: 
jorgen@6873:     for (i = 4; i >= 0; i--)
jorgen@6866:     {
jorgen@6873:         if (x & b[i])
jorgen@6873:         {
jorgen@6873:             x >>= S[i];
jorgen@6873:             msbIndex |= S[i];
jorgen@6873:         }
jorgen@6873:     }
jorgen@6866: 
jorgen@6873:     return msbIndex;
jorgen@6866: #endif
jorgen@6866: }
jorgen@6866: 
jorgen@6866: /* Ends C function definitions when using C++ */
jorgen@6866: #ifdef __cplusplus
jorgen@6866: /* *INDENT-OFF* */
jorgen@6866: }
jorgen@6866: /* *INDENT-ON* */
jorgen@6866: #endif
jorgen@6866: #include "close_code.h"
jorgen@6866: 
jorgen@6866: #endif /* _SDL_bits_h */
jorgen@6866: 
jorgen@6866: /* vi: set ts=4 sw=4 expandtab: */