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move PR1488 into this file.

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llvm-svn: 57579
This commit is contained in:
Chris Lattner 2008-10-15 16:02:15 +00:00
parent 981c5cde30
commit 4ccc775d89
1 changed files with 33 additions and 0 deletions
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33
lib/Target/README.txt
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@ -283,6 +283,39 @@ unsigned long reverse(unsigned v) {
//===---------------------------------------------------------------------===//
These idioms should be recognized as popcount (see PR1488):
unsigned countbits_slow(unsigned v) {
unsigned c;
for (c = 0; v; v >>= 1)
c += v & 1;
return c;
}
unsigned countbits_fast(unsigned v){
unsigned c;
for (c = 0; v; c++)
v &= v - 1; // clear the least significant bit set
return c;
}
BITBOARD = unsigned long long
int PopCnt(register BITBOARD a) {
register int c=0;
while(a) {
c++;
a &= a - 1;
}
return c;
}
unsigned int popcount(unsigned int input) {
unsigned int count = 0;
for (unsigned int i = 0; i < 4 * 8; i++)
count += (input >> i) & i;
return count;
}
//===---------------------------------------------------------------------===//
These should turn into single 16-bit (unaligned?) loads on little/big endian
processors.