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Avoid UB in maxIntN(64).

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Summary:
Previously we were relying on 2's complement underflow in an int64_t.
Now we cast to a uint64_t so we explicitly get the behavior we want.

Reviewers: rnk

Subscribers: dylanmckay, llvm-commits

Differential Revision: https://reviews.llvm.org/D22445

llvm-svn: 275722
This commit is contained in:
Justin Lebar 2016-07-17 18:19:26 +00:00
parent 070918a523
commit adedbb37b0
1 changed files with 3 additions and 1 deletions
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4
include/llvm/Support/MathExtras.h
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@ -344,7 +344,9 @@ inline int64_t minIntN(int64_t N) {
inline int64_t maxIntN(int64_t N) {
assert(N > 0 && N <= 64 && "integer width out of range");
return (INT64_C(1)<<(N-1)) - 1;
// This relies on two's complement wraparound when N == 64, so we convert to
// int64_t only at the very end to avoid UB.
return (UINT64_C(1) << (N - 1)) - 1;
}
/// isUIntN - Checks if an unsigned integer fits into the given (dynamic)