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ARM lsb/msb assembly

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Implement lsb/msb using armv7 assembly instructions.
msb is the easiest one, using a gcc intrinsic that generates
code using the ARM's clz instruction. lsb is also using this
clz instruction, but with the help of ARM's 'rbit' (bit
reversing) instruction. This leads to a >2% speed gain.

I also renamed 'arm-32' to the more meaningfull 'armv7' in the Makefile

No functional change.
This commit is contained in:
Jean-Francois Romang
2012-10-11 22:55:25 +08:00
committed by Marco Costalba
parent 4e7da9be3d
commit 7f9ebf8e86
2 changed files with 22 additions and 7 deletions
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15
src/bitboard.h
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@@ -247,6 +247,21 @@ FORCE_INLINE Square msb(Bitboard b) {
return (Square) index;
}
# elif defined(__arm__)
FORCE_INLINE int lsb32(uint32_t v) {
__asm__("rbit %0, %1" : "=r"(v) : "r"(v));
return __builtin_clz(v);
}
FORCE_INLINE Square msb(Bitboard b) {
return (Square) (63 - __builtin_clzll(b));
}
FORCE_INLINE Square lsb(Bitboard b) {
return (Square) (uint32_t(b) ? lsb32(uint32_t(b)) : 32 + lsb32(uint32_t(b >> 32)));
}
# else
FORCE_INLINE Square lsb(Bitboard b) { // Assembly code by Heinz van Saanen