}
unsigned APInt::countLeadingZerosSlowCase() const {
- // Treat the most significand word differently because it might have
- // meaningless bits set beyond the precision.
- unsigned BitsInMSW = BitWidth % APINT_BITS_PER_WORD;
- integerPart MSWMask;
- if (BitsInMSW) MSWMask = (integerPart(1) << BitsInMSW) - 1;
- else {
- MSWMask = ~integerPart(0);
- BitsInMSW = APINT_BITS_PER_WORD;
- }
-
- unsigned i = getNumWords();
- integerPart MSW = pVal[i-1] & MSWMask;
- if (MSW)
- return llvm::countLeadingZeros(MSW) - (APINT_BITS_PER_WORD - BitsInMSW);
-
- unsigned Count = BitsInMSW;
- for (--i; i > 0u; --i) {
- if (pVal[i-1] == 0)
+ unsigned Count = 0;
+ for (int i = getNumWords()-1; i >= 0; --i) {
+ integerPart V = pVal[i];
+ if (V == 0)
Count += APINT_BITS_PER_WORD;
else {
- Count += llvm::countLeadingZeros(pVal[i-1]);
+ Count += llvm::countLeadingZeros(V);
break;
}
}
+ // Adjust for unused bits in the most significant word (they are zero).
+ unsigned Mod = BitWidth % APINT_BITS_PER_WORD;
+ Count -= Mod > 0 ? APINT_BITS_PER_WORD - Mod : 0;
return Count;
}