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LibWasm: Make Absolute/Negate<SignedIntegral> explicitly work mod 2^N

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Previously we relied on signed overflow, this commit makes the same
behaviour explicit (avoiding UB in the process).
This commit is contained in:
Ali Mohammad Pur 2024-07-16 14:02:21 +02:00 • committed by Ali Mohammad Pur
parent 99824eae14
commit 8c8310f0bd
Notes: sideshowbarker 2024-07-17 01:46:00 +09:00
1 changed files with 24 additions and 2 deletions
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26
Userland/Libraries/LibWasm/AbstractMachine/Operators.h
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@ -505,14 +505,36 @@ struct PopCount {
struct Absolute {
template<typename Lhs>
auto operator()(Lhs lhs) const { return AK::abs(lhs); }
Lhs operator()(Lhs lhs) const
{
if constexpr (IsFloatingPoint<Lhs>)
return AK::abs(lhs);
if constexpr (IsSigned<Lhs>) {
if (lhs == NumericLimits<Lhs>::min())
return NumericLimits<Lhs>::min(); // Return the negation of _i_ modulo 2^N: https://www.w3.org/TR/wasm-core-2/#-hrefop-iabsmathrmiabs_n-i step 3
}
return AK::abs(lhs);
}
static StringView name() { return "abs"sv; }
};
struct Negate {
template<typename Lhs>
auto operator()(Lhs lhs) const { return -lhs; }
Lhs operator()(Lhs lhs) const
{
if constexpr (IsFloatingPoint<Lhs>)
return -lhs;
if constexpr (IsSigned<Lhs>) {
if (lhs == NumericLimits<Lhs>::min())
return NumericLimits<Lhs>::min(); // Return the negation of _i_ modulo 2^N: https://www.w3.org/TR/wasm-core-2/#-hrefop-iabsmathrmiabs_n-i step 3
}
return -lhs;
}
static StringView name() { return "== 0"sv; }
};