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author | skidd13 <skidd13@openttd.org> | 2007-11-26 17:50:22 +0000 |
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committer | skidd13 <skidd13@openttd.org> | 2007-11-26 17:50:22 +0000 |
commit | 71c10f7df7c1ec20bbc0c23580041a2e337b2500 (patch) | |
tree | 2e39f6768332621cf233165bcce1d8d2ee07f273 /src/core/bitmath_func.cpp | |
parent | 734b22e070ca1dac717780d0a4d1ca962c4ddfbf (diff) | |
download | openttd-71c10f7df7c1ec20bbc0c23580041a2e337b2500.tar.xz |
(svn r11527) -Codechange: Split the bitmath functions of to their own files
Diffstat (limited to 'src/core/bitmath_func.cpp')
-rw-r--r-- | src/core/bitmath_func.cpp | 45 |
1 files changed, 45 insertions, 0 deletions
diff --git a/src/core/bitmath_func.cpp b/src/core/bitmath_func.cpp new file mode 100644 index 000000000..9f36ed9a8 --- /dev/null +++ b/src/core/bitmath_func.cpp @@ -0,0 +1,45 @@ +/* $Id$ */ + +/** @file bitmath_func.cpp */ + +#include "../stdafx.h" +#include "bitmath_func.hpp" + +const uint8 _ffb_64[64] = { + 0, 0, 1, 0, 2, 0, 1, 0, + 3, 0, 1, 0, 2, 0, 1, 0, + 4, 0, 1, 0, 2, 0, 1, 0, + 3, 0, 1, 0, 2, 0, 1, 0, + 5, 0, 1, 0, 2, 0, 1, 0, + 3, 0, 1, 0, 2, 0, 1, 0, + 4, 0, 1, 0, 2, 0, 1, 0, + 3, 0, 1, 0, 2, 0, 1, 0, +}; + +/** + * Search the first set bit in a 32 bit variable. + * + * This algorithm is a static implementation of a log + * conguence search algorithm. It checks the first half + * if there is a bit set search there further. And this + * way further. If no bit is set return 0. + * + * @param x The value to search + * @param The position of the first bit set + */ +uint8 FindFirstBit(uint32 x) +{ + if (x == 0) return 0; + /* The macro FIND_FIRST_BIT is better to use when your x is + not more than 128. */ + + uint8 pos = 0; + + if ((x & 0x0000ffff) == 0) { x >>= 16; pos += 16; } + if ((x & 0x000000ff) == 0) { x >>= 8; pos += 8; } + if ((x & 0x0000000f) == 0) { x >>= 4; pos += 4; } + if ((x & 0x00000003) == 0) { x >>= 2; pos += 2; } + if ((x & 0x00000001) == 0) { pos += 1; } + + return pos; +} |