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Use the GCC built-in for PopulationCount when it's available, and use a faster

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algorithm when it's not.  This should be particularly noticeable in the
64-bit case.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@34776 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson 2007-03-01 05:41:28 +00:00
parent af8fb19846
commit 2a934cb607
1 changed files with 16 additions and 11 deletions
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27
include/llvm/Support/MathExtras.h
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@ -208,22 +208,27 @@ inline unsigned CountTrailingZeros_64(uint64_t Value) {
/// CountPopulation_32 - this function counts the number of set bits in a value. /// CountPopulation_32 - this function counts the number of set bits in a value.
/// Ex. CountPopulation(0xF000F000) = 8 /// Ex. CountPopulation(0xF000F000) = 8
/// Returns 0 if the word is zero. /// Returns 0 if the word is zero.
inline unsigned CountPopulation_32(unsigned Value) { inline unsigned CountPopulation_32(uint32_t Value) {
unsigned x, t; #if __GNUC__ >= 4
x = Value - ((Value >> 1) & 0x55555555); return __builtin_popcount(Value);
t = ((x >> 2) & 0x33333333); #else
x = (x & 0x33333333) + t; uint32_t v = v - ((v >> 1) & 0x55555555);
x = (x + (x >> 4)) & 0x0F0F0F0F; v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
x = x + (x << 8); return ((v + (v >> 4) & 0xF0F0F0F) * 0x1010101) >> 24;
x = x + (x << 16); #endif
return x >> 24;
} }
/// CountPopulation_64 - this function counts the number of set bits in a value, /// CountPopulation_64 - this function counts the number of set bits in a value,
/// (64 bit edition.) /// (64 bit edition.)
inline unsigned CountPopulation_64(uint64_t Value) { inline unsigned CountPopulation_64(uint64_t Value) {
return CountPopulation_32(unsigned(Value >> 32)) + #if __GNUC__ >= 4
CountPopulation_32(unsigned(Value)); return __builtin_popcountll(Value);
#else
uint64_t v = Value - ((Value >> 1) & 0x5555555555555555ULL);
v = (v & 0x3333333333333333ULL) + ((v >> 2) & 0x3333333333333333ULL);
v = (v + (v >> 4)) & 0x0F0F0F0F0F0F0F0FULL;
return (uint64_t)(v * 0x0101010101010101ULL) >> 56;
#endif
} }
/// Log2_32 - This function returns the floor log base 2 of the specified value, /// Log2_32 - This function returns the floor log base 2 of the specified value,