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LibJS: Add spec comments to unsigned_right_shift()

This commit is contained in:
Linus Groh 2022-12-10 00:07:17 +00:00
parent b66f9a8718
commit e27ef63217

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@ -1610,20 +1610,50 @@ ThrowCompletionOr<Value> right_shift(VM& vm, Value lhs, Value rhs)
}
// 13.9.3 The Unsigned Right Shift Operator ( >>> ), https://tc39.es/ecma262/#sec-unsigned-right-shift-operator
// ShiftExpression : ShiftExpression >>> AdditiveExpression
ThrowCompletionOr<Value> unsigned_right_shift(VM& vm, Value lhs, Value rhs)
{
// 13.15.3 ApplyStringOrNumericBinaryOperator ( lval, opText, rval ), https://tc39.es/ecma262/#sec-applystringornumericbinaryoperator
// 1-2, 5-6. 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)) {
// 6.1.6.1.11 Number::unsignedRightShift ( x, y ), https://tc39.es/ecma262/#sec-numeric-types-number-unsignedRightShift
// OPTIMIZATION: Handle infinite values according to the results returned by ToUint32.
if (!lhs_numeric.is_finite_number())
return Value(0);
if (!rhs_numeric.is_finite_number())
return lhs_numeric;
// Ok, so this performs toNumber() again but that "can't" throw
// 1. Let lnum be ! ToUint32(x).
auto lhs_u32 = MUST(lhs_numeric.to_u32(vm));
auto rhs_u32 = MUST(rhs_numeric.to_u32(vm)) % 32;
return Value(lhs_u32 >> rhs_u32);
// 2. Let rnum be ! ToUint32(y).
auto rhs_u32 = MUST(rhs_numeric.to_u32(vm));
// 3. Let shiftCount be (rnum) modulo 32.
auto shift_count = rhs_u32 % 32;
// 4. Return the result of performing a zero-filling right shift of lnum by shiftCount bits.
// Vacated bits are filled with zero. The mathematical value of the result is exactly representable
// as a 32-bit unsigned bit string.
return Value(lhs_u32 >> shift_count);
}
// 6. If lnum is a BigInt, then
// d. If opText is >>>, return ? BigInt::unsignedRightShift(lnum, rnum).
// 6.1.6.2.11 BigInt::unsignedRightShift ( x, y ), https://tc39.es/ecma262/#sec-numeric-types-bigint-unsignedRightShift
// 1. Throw a TypeError exception.
return vm.throw_completion<TypeError>(ErrorType::BigIntBadOperator, "unsigned right-shift");
}