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Don't do uint64_t(1) << 64 in maxUIntN.

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Summary:
This shift is undefined behavior (and, as compiled by clang, gives the
wrong answer for maxUIntN(64)).

Reviewers: mkuper

Subscribers: llvm-commits, jroelofs, rsmith

Differential Revision: https://reviews.llvm.org/D22430

llvm-svn: 275656
This commit is contained in:
Justin Lebar 2016-07-16 00:59:41 +00:00
parent 88667faa02
commit 914e437454
2 changed files with 4 additions and 0 deletions
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3
include/llvm/Support/MathExtras.h
View File

@ -316,6 +316,9 @@ inline bool isShiftedUInt(uint64_t x) {
inline uint64_t maxUIntN(uint64_t N) {
assert(N > 0 && N <= 64 && "integer width out of range");
// uint64_t(1) << 64 is undefined behavior.
if (N == 64)
return std::numeric_limits<uint64_t>::max();
return (UINT64_C(1) << N) - 1;
}

1
unittests/Support/MathExtrasTest.cpp
View File

@ -131,6 +131,7 @@ TEST(MathExtras, minIntN) {
TEST(MathExtras, maxUIntN) {
EXPECT_EQ(0xffffULL, maxUIntN(16));
EXPECT_EQ(0xffffffffULL, maxUIntN(32));
EXPECT_EQ(0xffffffffffffffffULL, maxUIntN(64));
EXPECT_EQ(1ULL, maxUIntN(1));
EXPECT_EQ(0x0fULL, maxUIntN(4));
}