include/SDL_bits.h
author Ozkan Sezer
Mon, 25 Jan 2021 04:11:40 +0300
changeset 14792 d01593bd58d9
parent 14656 344fc6fca09e
permissions -rw-r--r--
better check for clock_gettime_nsec_np() -- cf. bug #5467.
     1 /*
     2   Simple DirectMedia Layer
     3   Copyright (C) 1997-2021 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_bsr_watcom (Uint32);
    52 #pragma aux _SDL_bsr_watcom = \
    53     "bsr eax, eax" \
    54     parm [eax] nomemory \
    55     value [eax] \
    56     modify exact [eax] nomemory;
    57 #endif
    58 
    59 SDL_FORCE_INLINE int
    60 SDL_MostSignificantBitIndex32(Uint32 x)
    61 {
    62 #if defined(__GNUC__) && (__GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
    63     /* Count Leading Zeroes builtin in GCC.
    64      * http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html
    65      */
    66     if (x == 0) {
    67         return -1;
    68     }
    69     return 31 - __builtin_clz(x);
    70 #elif defined(__WATCOMC__) && defined(__386__)
    71     if (x == 0) {
    72         return -1;
    73     }
    74     return _SDL_bsr_watcom(x);
    75 #elif defined(_MSC_VER)
    76     unsigned long index;
    77     if (_BitScanReverse(&index, x)) {
    78         return index;
    79     }
    80     return -1;
    81 #else
    82     /* Based off of Bit Twiddling Hacks by Sean Eron Anderson
    83      * <seander@cs.stanford.edu>, released in the public domain.
    84      * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
    85      */
    86     const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000};
    87     const int    S[] = {1, 2, 4, 8, 16};
    88 
    89     int msbIndex = 0;
    90     int i;
    91 
    92     if (x == 0) {
    93         return -1;
    94     }
    95 
    96     for (i = 4; i >= 0; i--)
    97     {
    98         if (x & b[i])
    99         {
   100             x >>= S[i];
   101             msbIndex |= S[i];
   102         }
   103     }
   104 
   105     return msbIndex;
   106 #endif
   107 }
   108 
   109 SDL_FORCE_INLINE SDL_bool
   110 SDL_HasExactlyOneBitSet32(Uint32 x)
   111 {
   112     if (x && !(x & (x - 1))) {
   113         return SDL_TRUE;
   114     }
   115     return SDL_FALSE;
   116 }
   117 
   118 /* Ends C function definitions when using C++ */
   119 #ifdef __cplusplus
   120 }
   121 #endif
   122 #include "close_code.h"
   123 
   124 #endif /* SDL_bits_h_ */
   125 
   126 /* vi: set ts=4 sw=4 expandtab: */