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Compute getLowBitsSet correctly. Using the complement of a 64-bit value

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and shifting down without regard for the bitwidth of the APInt can lead
to incorrect initialization values. Instead, check for the word size case
(to avoid undef results from shift) and then do (1 << loBitsSet) - 1


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@35344 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Reid Spencer 2007-03-25 21:58:42 +00:00
parent 9031aca96b
commit f6bef488ee
1 changed files with 5 additions and 4 deletions
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9
include/llvm/ADT/APInt.h
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@ -374,11 +374,12 @@ public:
// Handle a degenerate case, to avoid shifting by word size
if (loBitsSet == 0)
return APInt(numBits, 0);
uint32_t shiftAmt = numBits - loBitsSet;
if (loBitsSet == APINT_BITS_PER_WORD)
return APInt(numBits, -1ULL);
// For small values, return quickly
if (numBits <= APINT_BITS_PER_WORD)
return APInt(numBits, ~0ULL >> shiftAmt);
return (~APInt(numBits, 0)).lshr(shiftAmt);
if (numBits < APINT_BITS_PER_WORD)
return APInt(numBits, (1ULL << loBitsSet) - 1);
return (~APInt(numBits, 0)).lshr(numBits - loBitsSet);
}
/// The hash value is computed as the sum of the words and the bit width.