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LibJS: Add spec comments to right_shift()

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Linus Groh 2022-12-10 00:07:00 +00:00
parent 8aa19a8a60
commit b66f9a8718
1 changed files with 31 additions and 2 deletions
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33
Userland/Libraries/LibJS/Runtime/Value.cpp
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@ -1559,24 +1559,53 @@ ThrowCompletionOr<Value> left_shift(VM& vm, Value lhs, Value rhs)
}
// 13.9.2 The Signed Right Shift Operator ( >> ), https://tc39.es/ecma262/#sec-signed-right-shift-operator
// ShiftExpression : ShiftExpression >> AdditiveExpression
ThrowCompletionOr<Value> right_shift(VM& vm, Value lhs, Value rhs)
{
// 13.15.3 ApplyStringOrNumericBinaryOperator ( lval, opText, rval ), https://tc39.es/ecma262/#sec-applystringornumericbinaryoperator
// 1-2, 6. N/A.
// 3. Let lnum be ? ToNumeric(lval).
auto lhs_numeric = TRY(lhs.to_numeric(vm));
// 4. Let rnum be ? ToNumeric(rval).
auto rhs_numeric = TRY(rhs.to_numeric(vm));
// 7. Let operation be the abstract operation associated with opText and Type(lnum) in the following table:
// [...]
// 8. Return operation(lnum, rnum).
if (both_number(lhs_numeric, rhs_numeric)) {
// 6.1.6.1.10 Number::signedRightShift ( x, y ), https://tc39.es/ecma262/#sec-numeric-types-number-signedRightShift
// OPTIMIZATION: Handle infinite values according to the results returned by ToInt32/ToUint32.
if (!lhs_numeric.is_finite_number())
return Value(0);
if (!rhs_numeric.is_finite_number())
return lhs_numeric;
// 1. Let lnum be ! ToInt32(x).
auto lhs_i32 = MUST(lhs_numeric.to_i32(vm));
auto rhs_u32 = MUST(rhs_numeric.to_u32(vm)) % 32;
return Value(lhs_i32 >> rhs_u32);
// 2. Let rnum be ! ToUint32(y).
auto rhs_u32 = MUST(rhs_numeric.to_u32(vm));
// 3. Let shiftCount be ℝ(rnum) modulo 32.
auto shift_count = rhs_u32 % 32;
// 4. Return the result of performing a sign-extending right shift of lnum by shiftCount bits.
// The most significant bit is propagated. The mathematical value of the result is exactly representable
// as a 32-bit two's complement bit string.
return Value(lhs_i32 >> shift_count);
}
if (both_bigint(lhs_numeric, rhs_numeric)) {
// 6.1.6.2.10 BigInt::signedRightShift ( x, y ), https://tc39.es/ecma262/#sec-numeric-types-bigint-signedRightShift
// 1. Return BigInt::leftShift(x, -y).
auto rhs_negated = rhs_numeric.as_bigint().big_integer();
rhs_negated.negate();
return left_shift(vm, lhs, BigInt::create(vm, rhs_negated));
}
// 5. If Type(lnum) is different from Type(rnum), throw a TypeError exception.
return vm.throw_completion<TypeError>(ErrorType::BigIntBadOperatorOtherType, "right-shift");
}