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BitUtils: Add CountLeadingZeros

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This commit is contained in:
MerryMage
2020-12-27 22:37:37 +00:00
parent 4705af59c6
commit d695fcb126
4 changed files with 52 additions and 45 deletions
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24
Source/Core/Common/Arm64Emitter.cpp
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@ -26,20 +26,6 @@ namespace
const int kWRegSizeInBits = 32;
const int kXRegSizeInBits = 64;
// The below few functions are taken from V8.
int CountLeadingZeros(uint64_t value, int width)
{
// TODO(jbramley): Optimize this for ARM64 hosts.
int count = 0;
uint64_t bit_test = 1ULL << (width - 1);
while ((count < width) && ((bit_test & value) == 0))
{
count++;
bit_test >>= 1;
}
return count;
}
uint64_t LargestPowerOf2Divisor(uint64_t value)
{
return value & -(int64_t)value;
@ -155,8 +141,8 @@ bool IsImmLogical(uint64_t value, unsigned int width, unsigned int* n, unsigned
// Compute the repeat distance d, and set up a bitmask covering the basic
// unit of repetition (i.e. a word with the bottom d bits set). Also, in all
// of these cases the N bit of the output will be zero.
clz_a = CountLeadingZeros(a, kXRegSizeInBits);
int clz_c = CountLeadingZeros(c, kXRegSizeInBits);
clz_a = Common::CountLeadingZeros(a);
int clz_c = Common::CountLeadingZeros(c);
d = clz_a - clz_c;
mask = ((UINT64_C(1) << d) - 1);
out_n = 0;
@ -182,7 +168,7 @@ bool IsImmLogical(uint64_t value, unsigned int width, unsigned int* n, unsigned
// of set bits in our word, meaning that we have the trivial case of
// d == 64 and only one 'repetition'. Set up all the same variables as in
// the general case above, and set the N bit in the output.
clz_a = CountLeadingZeros(a, kXRegSizeInBits);
clz_a = Common::CountLeadingZeros(a);
d = 64;
mask = ~UINT64_C(0);
out_n = 1;
@ -214,7 +200,7 @@ bool IsImmLogical(uint64_t value, unsigned int width, unsigned int* n, unsigned
0x5555555555555555UL,
}};
int multiplier_idx = CountLeadingZeros(d, kXRegSizeInBits) - 57;
int multiplier_idx = Common::CountLeadingZeros((u64)d) - 57;
// Ensure that the index to the multipliers array is within bounds.
DEBUG_ASSERT((multiplier_idx >= 0) && (static_cast<size_t>(multiplier_idx) < multipliers.size()));
@ -233,7 +219,7 @@ bool IsImmLogical(uint64_t value, unsigned int width, unsigned int* n, unsigned
// Count the set bits in our basic stretch. The special case of clz(0) == -1
// makes the answer come out right for stretches that reach the very top of
// the word (e.g. numbers like 0xffffc00000000000).
int clz_b = (b == 0) ? -1 : CountLeadingZeros(b, kXRegSizeInBits);
int clz_b = (b == 0) ? -1 : Common::CountLeadingZeros(b);
int s = clz_a - clz_b;
// Decide how many bits to rotate right by, to put the low bit of that basic