include/SDL_bits.h
author Sam Lantinga <slouken@libsdl.org>
Sat, 18 May 2013 12:48:50 -0700
changeset 7190 11612d544fcd
parent 7033 3b12bae22f9e
child 7191 75360622e65f
permissions -rw-r--r--
Added mobile application events, with implementations for iOS and Android
     1 /*
     2   Simple DirectMedia Layer
     3   Copyright (C) 1997-2013 Sam Lantinga <slouken@libsdl.org>
     4 
     5   This software is provided 'as-is', without any express or implied
     6   warranty.  In no event will the authors be held liable for any damages
     7   arising from the use of this software.
     8 
     9   Permission is granted to anyone to use this software for any purpose,
    10   including commercial applications, and to alter it and redistribute it
    11   freely, subject to the following restrictions:
    12 
    13   1. The origin of this software must not be misrepresented; you must not
    14      claim that you wrote the original software. If you use this software
    15      in a product, an acknowledgment in the product documentation would be
    16      appreciated but is not required.
    17   2. Altered source versions must be plainly marked as such, and must not be
    18      misrepresented as being the original software.
    19   3. This notice may not be removed or altered from any source distribution.
    20 */
    21 
    22 /**
    23  *  \file SDL_bits.h
    24  *
    25  *  Functions for fiddling with bits and bitmasks.
    26  */
    27 
    28 #ifndef _SDL_bits_h
    29 #define _SDL_bits_h
    30 
    31 #include "SDL_stdinc.h"
    32 
    33 #include "begin_code.h"
    34 /* Set up for C function definitions, even when using C++ */
    35 #ifdef __cplusplus
    36 /* *INDENT-OFF* */
    37 extern "C" {
    38 /* *INDENT-ON* */
    39 #endif
    40 
    41 /**
    42  *  \file SDL_bits.h
    43  */
    44 
    45 /**
    46  *  Get the index of the most significant bit. Result is undefined when called
    47  *  with 0. This operation can also be stated as "count leading zeroes" and
    48  *  "log base 2".
    49  *
    50  *  \return Index of the most significant bit.
    51  */
    52 SDL_FORCE_INLINE Sint8
    53 SDL_MostSignificantBitIndex32(Uint32 x)
    54 {
    55 #if defined(__GNUC__) && __GNUC__ >= 4
    56     /* Count Leading Zeroes builtin in GCC.
    57      * http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html
    58      */
    59     return 31 - __builtin_clz(x);
    60 #else
    61     /* Based off of Bit Twiddling Hacks by Sean Eron Anderson
    62      * <seander@cs.stanford.edu>, released in the public domain.
    63      * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
    64      */
    65     const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
    66     const Uint8  S[] = {1, 2, 4, 8, 16};
    67 
    68     Uint8 msbIndex = 0;
    69     int i;
    70 
    71     for (i = 4; i >= 0; i--)
    72     {
    73         if (x & b[i])
    74         {
    75             x >>= S[i];
    76             msbIndex |= S[i];
    77         }
    78     }
    79 
    80     return msbIndex;
    81 #endif
    82 }
    83 
    84 /* Ends C function definitions when using C++ */
    85 #ifdef __cplusplus
    86 /* *INDENT-OFF* */
    87 }
    88 /* *INDENT-ON* */
    89 #endif
    90 #include "close_code.h"
    91 
    92 #endif /* _SDL_bits_h */
    93 
    94 /* vi: set ts=4 sw=4 expandtab: */