include/SDL_bits.h
author Ozkan Sezer <sezeroz@gmail.com>
Thu, 16 Aug 2018 11:01:02 +0300
changeset 12120 0131b11bd03f
parent 11811 5d94cb6b24d3
permissions -rw-r--r--
SDL_hidapi_ps4.c: define NTDDI_VISTA / _WIN32_WINNT_VISTA if not defined

it still needs a Vista or newer Platform SDK to build, though.
     1 /*
     2   Simple DirectMedia Layer
     3   Copyright (C) 1997-2018 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 extern "C" {
    37 #endif
    38 
    39 /**
    40  *  \file SDL_bits.h
    41  */
    42 
    43 /**
    44  *  Get the index of the most significant bit. Result is undefined when called
    45  *  with 0. This operation can also be stated as "count leading zeroes" and
    46  *  "log base 2".
    47  *
    48  *  \return Index of the most significant bit, or -1 if the value is 0.
    49  */
    50 #if defined(__WATCOMC__) && defined(__386__)
    51 extern _inline int _SDL_clz_watcom (Uint32);
    52 #pragma aux _SDL_clz_watcom = \
    53     "bsr eax, eax" \
    54     "xor eax, 31" \
    55     parm [eax] nomemory \
    56     value [eax] \
    57     modify exact [eax] nomemory;
    58 #endif
    59 
    60 SDL_FORCE_INLINE int
    61 SDL_MostSignificantBitIndex32(Uint32 x)
    62 {
    63 #if defined(__GNUC__) && (__GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
    64     /* Count Leading Zeroes builtin in GCC.
    65      * http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html
    66      */
    67     if (x == 0) {
    68         return -1;
    69     }
    70     return 31 - __builtin_clz(x);
    71 #elif defined(__WATCOMC__) && defined(__386__)
    72     if (x == 0) {
    73         return -1;
    74     }
    75     return 31 - _SDL_clz_watcom(x);
    76 #else
    77     /* Based off of Bit Twiddling Hacks by Sean Eron Anderson
    78      * <seander@cs.stanford.edu>, released in the public domain.
    79      * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
    80      */
    81     const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
    82     const int    S[] = {1, 2, 4, 8, 16};
    83 
    84     int msbIndex = 0;
    85     int i;
    86 
    87     if (x == 0) {
    88         return -1;
    89     }
    90 
    91     for (i = 4; i >= 0; i--)
    92     {
    93         if (x & b[i])
    94         {
    95             x >>= S[i];
    96             msbIndex |= S[i];
    97         }
    98     }
    99 
   100     return msbIndex;
   101 #endif
   102 }
   103 
   104 /* Ends C function definitions when using C++ */
   105 #ifdef __cplusplus
   106 }
   107 #endif
   108 #include "close_code.h"
   109 
   110 #endif /* SDL_bits_h_ */
   111 
   112 /* vi: set ts=4 sw=4 expandtab: */