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fix undefined left shift of negative int in math.bitShiftLeft #2044

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fix undefined left shift of negative int in math.bitShiftLeft #2044

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6 changes: 5 additions & 1 deletion extensions/math_ext.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -266,7 +266,11 @@ Value BitShiftLeftInt(int64_t lhs, int64_t rhs) {
if (rhs > 63) {
return IntValue(0);
}
return IntValue(lhs << static_cast<int>(rhs));
// Shift in the unsigned domain to avoid undefined behaviour when lhs is
// negative or the shift moves bits into the sign bit, matching the bit
// pattern semantics already used by bitShiftRight.
return IntValue(absl::bit_cast<int64_t>(absl::bit_cast<uint64_t>(lhs)
<< static_cast<int>(rhs)));
}

Value BitShiftLeftUint(uint64_t lhs, int64_t rhs) {
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2 changes: 2 additions & 0 deletions extensions/math_ext_test.cc
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Expand Up @@ -563,6 +563,8 @@ INSTANTIATE_TEST_SUITE_P(
{"math.bitNot(2) == -3"},
{"math.bitAnd(math.bitNot(0x3u), 0xFFu) == 0xFCu"},
{"math.bitShiftLeft(1, 1) == 2"},
{"math.bitShiftLeft(-1, 1) == -2"},
{"math.bitShiftLeft(-4, 2) == -16"},
{"math.bitShiftLeft(1u, 1) == 2u"},
{"math.bitShiftRight(4, 1) == 2"},
{"math.bitShiftRight(4u, 1) == 2u"}}));
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