include/SDL_bits.h
author David Ludwig <dludwig@pobox.com>
Mon, 01 Apr 2013 21:33:06 -0400
changeset 8453 499aa167ea79
parent 6873 f042ae287155
child 7004 18d4df6942c2
permissions -rw-r--r--
WinRT: made WinRT path retrieval be available in both UCS-2 and UTF-8 flavors
     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  *  Uses inline functions for compilers that support them, and static
    45  *  functions for those that do not.  Because these functions become
    46  *  static for compilers that do not support inline functions, this
    47  *  header should only be included in files that actually use them.
    48  */
    49 
    50 /**
    51  *  Get the index of the most significant bit. Result is undefined when called
    52  *  with 0. This operation can also be stated as "count leading zeroes" and
    53  *  "log base 2".
    54  *
    55  *  \return Index of the most significant bit.
    56  */
    57 static __inline__ Sint8
    58 SDL_MostSignificantBitIndex32(Uint32 x)
    59 {
    60 #if defined(__GNUC__)
    61     /* Count Leading Zeroes builtin in GCC.
    62      * http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html
    63      */
    64     return 31 - __builtin_clz(x);
    65 #else
    66     /* Based off of Bit Twiddling Hacks by Sean Eron Anderson
    67      * <seander@cs.stanford.edu>, released in the public domain.
    68      * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
    69      */
    70     const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
    71     const Uint8  S[] = {1, 2, 4, 8, 16};
    72 
    73     Uint8 msbIndex = 0;
    74     int i;
    75 
    76     for (i = 4; i >= 0; i--)
    77     {
    78         if (x & b[i])
    79         {
    80             x >>= S[i];
    81             msbIndex |= S[i];
    82         }
    83     }
    84 
    85     return msbIndex;
    86 #endif
    87 }
    88 
    89 /* Ends C function definitions when using C++ */
    90 #ifdef __cplusplus
    91 /* *INDENT-OFF* */
    92 }
    93 /* *INDENT-ON* */
    94 #endif
    95 #include "close_code.h"
    96 
    97 #endif /* _SDL_bits_h */
    98 
    99 /* vi: set ts=4 sw=4 expandtab: */