SDL Library
SDL_bits.h@0:7fb6877b5d7c, 2016-09-22 (annotated)
- Committer:
- miruga27
- Date:
- Thu Sep 22 00:03:09 2016 +0000
- Revision:
- 0:7fb6877b5d7c
SDL
Who changed what in which revision?
User | Revision | Line number | New contents of line |
---|---|---|---|
miruga27 | 0:7fb6877b5d7c | 1 | /* |
miruga27 | 0:7fb6877b5d7c | 2 | Simple DirectMedia Layer |
miruga27 | 0:7fb6877b5d7c | 3 | Copyright (C) 1997-2014 Sam Lantinga <slouken@libsdl.org> |
miruga27 | 0:7fb6877b5d7c | 4 | |
miruga27 | 0:7fb6877b5d7c | 5 | This software is provided 'as-is', without any express or implied |
miruga27 | 0:7fb6877b5d7c | 6 | warranty. In no event will the authors be held liable for any damages |
miruga27 | 0:7fb6877b5d7c | 7 | arising from the use of this software. |
miruga27 | 0:7fb6877b5d7c | 8 | |
miruga27 | 0:7fb6877b5d7c | 9 | Permission is granted to anyone to use this software for any purpose, |
miruga27 | 0:7fb6877b5d7c | 10 | including commercial applications, and to alter it and redistribute it |
miruga27 | 0:7fb6877b5d7c | 11 | freely, subject to the following restrictions: |
miruga27 | 0:7fb6877b5d7c | 12 | |
miruga27 | 0:7fb6877b5d7c | 13 | 1. The origin of this software must not be misrepresented; you must not |
miruga27 | 0:7fb6877b5d7c | 14 | claim that you wrote the original software. If you use this software |
miruga27 | 0:7fb6877b5d7c | 15 | in a product, an acknowledgment in the product documentation would be |
miruga27 | 0:7fb6877b5d7c | 16 | appreciated but is not required. |
miruga27 | 0:7fb6877b5d7c | 17 | 2. Altered source versions must be plainly marked as such, and must not be |
miruga27 | 0:7fb6877b5d7c | 18 | misrepresented as being the original software. |
miruga27 | 0:7fb6877b5d7c | 19 | 3. This notice may not be removed or altered from any source distribution. |
miruga27 | 0:7fb6877b5d7c | 20 | */ |
miruga27 | 0:7fb6877b5d7c | 21 | |
miruga27 | 0:7fb6877b5d7c | 22 | /** |
miruga27 | 0:7fb6877b5d7c | 23 | * \file SDL_bits.h |
miruga27 | 0:7fb6877b5d7c | 24 | * |
miruga27 | 0:7fb6877b5d7c | 25 | * Functions for fiddling with bits and bitmasks. |
miruga27 | 0:7fb6877b5d7c | 26 | */ |
miruga27 | 0:7fb6877b5d7c | 27 | |
miruga27 | 0:7fb6877b5d7c | 28 | #ifndef _SDL_bits_h |
miruga27 | 0:7fb6877b5d7c | 29 | #define _SDL_bits_h |
miruga27 | 0:7fb6877b5d7c | 30 | |
miruga27 | 0:7fb6877b5d7c | 31 | #include "SDL_stdinc.h" |
miruga27 | 0:7fb6877b5d7c | 32 | |
miruga27 | 0:7fb6877b5d7c | 33 | #include "begin_code.h" |
miruga27 | 0:7fb6877b5d7c | 34 | /* Set up for C function definitions, even when using C++ */ |
miruga27 | 0:7fb6877b5d7c | 35 | #ifdef __cplusplus |
miruga27 | 0:7fb6877b5d7c | 36 | extern "C" { |
miruga27 | 0:7fb6877b5d7c | 37 | #endif |
miruga27 | 0:7fb6877b5d7c | 38 | |
miruga27 | 0:7fb6877b5d7c | 39 | /** |
miruga27 | 0:7fb6877b5d7c | 40 | * \file SDL_bits.h |
miruga27 | 0:7fb6877b5d7c | 41 | */ |
miruga27 | 0:7fb6877b5d7c | 42 | |
miruga27 | 0:7fb6877b5d7c | 43 | /** |
miruga27 | 0:7fb6877b5d7c | 44 | * Get the index of the most significant bit. Result is undefined when called |
miruga27 | 0:7fb6877b5d7c | 45 | * with 0. This operation can also be stated as "count leading zeroes" and |
miruga27 | 0:7fb6877b5d7c | 46 | * "log base 2". |
miruga27 | 0:7fb6877b5d7c | 47 | * |
miruga27 | 0:7fb6877b5d7c | 48 | * \return Index of the most significant bit, or -1 if the value is 0. |
miruga27 | 0:7fb6877b5d7c | 49 | */ |
miruga27 | 0:7fb6877b5d7c | 50 | SDL_FORCE_INLINE int |
miruga27 | 0:7fb6877b5d7c | 51 | SDL_MostSignificantBitIndex32(Uint32 x) |
miruga27 | 0:7fb6877b5d7c | 52 | { |
miruga27 | 0:7fb6877b5d7c | 53 | #if defined(__GNUC__) && __GNUC__ >= 4 |
miruga27 | 0:7fb6877b5d7c | 54 | /* Count Leading Zeroes builtin in GCC. |
miruga27 | 0:7fb6877b5d7c | 55 | * http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Other-Builtins.html |
miruga27 | 0:7fb6877b5d7c | 56 | */ |
miruga27 | 0:7fb6877b5d7c | 57 | if (x == 0) { |
miruga27 | 0:7fb6877b5d7c | 58 | return -1; |
miruga27 | 0:7fb6877b5d7c | 59 | } |
miruga27 | 0:7fb6877b5d7c | 60 | return 31 - __builtin_clz(x); |
miruga27 | 0:7fb6877b5d7c | 61 | #else |
miruga27 | 0:7fb6877b5d7c | 62 | /* Based off of Bit Twiddling Hacks by Sean Eron Anderson |
miruga27 | 0:7fb6877b5d7c | 63 | * <seander@cs.stanford.edu>, released in the public domain. |
miruga27 | 0:7fb6877b5d7c | 64 | * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog |
miruga27 | 0:7fb6877b5d7c | 65 | */ |
miruga27 | 0:7fb6877b5d7c | 66 | const Uint32 b[] = {0x2, 0xC, 0xF0, 0xFF00, 0xFFFF0000}; |
miruga27 | 0:7fb6877b5d7c | 67 | const int S[] = {1, 2, 4, 8, 16}; |
miruga27 | 0:7fb6877b5d7c | 68 | |
miruga27 | 0:7fb6877b5d7c | 69 | int msbIndex = 0; |
miruga27 | 0:7fb6877b5d7c | 70 | int i; |
miruga27 | 0:7fb6877b5d7c | 71 | |
miruga27 | 0:7fb6877b5d7c | 72 | if (x == 0) { |
miruga27 | 0:7fb6877b5d7c | 73 | return -1; |
miruga27 | 0:7fb6877b5d7c | 74 | } |
miruga27 | 0:7fb6877b5d7c | 75 | |
miruga27 | 0:7fb6877b5d7c | 76 | for (i = 4; i >= 0; i--) |
miruga27 | 0:7fb6877b5d7c | 77 | { |
miruga27 | 0:7fb6877b5d7c | 78 | if (x & b[i]) |
miruga27 | 0:7fb6877b5d7c | 79 | { |
miruga27 | 0:7fb6877b5d7c | 80 | x >>= S[i]; |
miruga27 | 0:7fb6877b5d7c | 81 | msbIndex |= S[i]; |
miruga27 | 0:7fb6877b5d7c | 82 | } |
miruga27 | 0:7fb6877b5d7c | 83 | } |
miruga27 | 0:7fb6877b5d7c | 84 | |
miruga27 | 0:7fb6877b5d7c | 85 | return msbIndex; |
miruga27 | 0:7fb6877b5d7c | 86 | #endif |
miruga27 | 0:7fb6877b5d7c | 87 | } |
miruga27 | 0:7fb6877b5d7c | 88 | |
miruga27 | 0:7fb6877b5d7c | 89 | /* Ends C function definitions when using C++ */ |
miruga27 | 0:7fb6877b5d7c | 90 | #ifdef __cplusplus |
miruga27 | 0:7fb6877b5d7c | 91 | } |
miruga27 | 0:7fb6877b5d7c | 92 | #endif |
miruga27 | 0:7fb6877b5d7c | 93 | #include "close_code.h" |
miruga27 | 0:7fb6877b5d7c | 94 | |
miruga27 | 0:7fb6877b5d7c | 95 | #endif /* _SDL_bits_h */ |
miruga27 | 0:7fb6877b5d7c | 96 | |
miruga27 | 0:7fb6877b5d7c | 97 | /* vi: set ts=4 sw=4 expandtab: */ |