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LibJS: Add spec comments to Value::to_i8()

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This commit is contained in:
Linus Groh 2022-12-10 00:01:58 +00:00
parent 42eac3b7d3
commit 2a3f150ab8
1 changed files with 13 additions and 4 deletions
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17
Userland/Libraries/LibJS/Runtime/Value.cpp
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@ -983,15 +983,24 @@ ThrowCompletionOr<u16> Value::to_u16(VM& vm) const
// 7.1.10 ToInt8 ( argument ), https://tc39.es/ecma262/#sec-toint8
ThrowCompletionOr<i8> Value::to_i8(VM& vm) const
{
double value = TRY(to_number(vm)).as_double();
if (!isfinite(value) || value == 0)
// 1. Let number be ? ToNumber(argument).
double number = TRY(to_number(vm)).as_double();
// 2. If number is not finite or number is either +0𝔽 or -0𝔽, return +0𝔽.
if (!isfinite(number) || number == 0)
return 0;
auto abs = fabs(value);
// 3. Let int be the mathematical value whose sign is the sign of number and whose magnitude is floor(abs(ℝ(number))).
auto abs = fabs(number);
auto int_val = floor(abs);
if (signbit(value))
if (signbit(number))
int_val = -int_val;
// 4. Let int8bit be int modulo 2^8.
auto remainder = fmod(int_val, 256.0);
auto int8bit = remainder >= 0.0 ? remainder : remainder + 256.0; // The notation “x modulo y” computes a value k of the same sign as y
// 5. If int8bit ≥ 2^7, return 𝔽(int8bit - 2^8); otherwise return 𝔽(int8bit).
if (int8bit >= 128.0)
int8bit -= 256.0;
return static_cast<i8>(int8bit);