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LibJS: Add spec comments to unary_minus()

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Linus Groh 2022-12-10 00:06:16 +00:00
parent 4458b7bf19
commit 08f6be1715
1 changed files with 30 additions and 6 deletions
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36
Userland/Libraries/LibJS/Runtime/Value.cpp
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@ -1456,17 +1456,41 @@ ThrowCompletionOr<Value> unary_plus(VM& vm, Value lhs)
}
// 13.5.5 Unary - Operator, https://tc39.es/ecma262/#sec-unary-minus-operator
// UnaryExpression : - UnaryExpression
ThrowCompletionOr<Value> unary_minus(VM& vm, Value lhs)
{
auto lhs_numeric = TRY(lhs.to_numeric(vm));
if (lhs_numeric.is_number()) {
if (lhs_numeric.is_nan())
// 1. Let expr be ? Evaluation of UnaryExpression.
// NOTE: This is handled in the AST or Bytecode interpreter.
// 2. Let oldValue be ? ToNumeric(? GetValue(expr)).
auto old_value = TRY(lhs.to_numeric(vm));
// 3. If oldValue is a Number, then
if (old_value.is_number()) {
// a. Return Number::unaryMinus(oldValue).
// 6.1.6.1.1 Number::unaryMinus ( x ), https://tc39.es/ecma262/#sec-numeric-types-number-unaryMinus
// 1. If x is NaN, return NaN.
if (old_value.is_nan())
return js_nan();
return Value(-lhs_numeric.as_double());
// 2. Return the result of negating x; that is, compute a Number with the same magnitude but opposite sign.
return Value(-old_value.as_double());
}
if (lhs_numeric.as_bigint().big_integer() == BIGINT_ZERO)
// 4. Else,
// a. Assert: oldValue is a BigInt.
VERIFY(old_value.is_bigint());
// b. Return BigInt::unaryMinus(oldValue).
// 6.1.6.2.1 BigInt::unaryMinus ( x ), https://tc39.es/ecma262/#sec-numeric-types-bigint-unaryMinus
// 1. If x is 0ℤ, return 0ℤ.
if (old_value.as_bigint().big_integer() == BIGINT_ZERO)
return BigInt::create(vm, BIGINT_ZERO);
auto big_integer_negated = lhs_numeric.as_bigint().big_integer();
// 2. Return the BigInt value that represents the negation of ℝ(x).
auto big_integer_negated = old_value.as_bigint().big_integer();
big_integer_negated.negate();
return BigInt::create(vm, big_integer_negated);
}