From 2a3f150ab83ff554de82bf77fe37046fb4a30e92 Mon Sep 17 00:00:00 2001 From: Linus Groh Date: Sat, 10 Dec 2022 00:01:58 +0000 Subject: [PATCH] LibJS: Add spec comments to Value::to_i8() --- Userland/Libraries/LibJS/Runtime/Value.cpp | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/Userland/Libraries/LibJS/Runtime/Value.cpp b/Userland/Libraries/LibJS/Runtime/Value.cpp index 2b336de147..e6d799bcd9 100644 --- a/Userland/Libraries/LibJS/Runtime/Value.cpp +++ b/Userland/Libraries/LibJS/Runtime/Value.cpp @@ -983,15 +983,24 @@ ThrowCompletionOr Value::to_u16(VM& vm) const // 7.1.10 ToInt8 ( argument ), https://tc39.es/ecma262/#sec-toint8 ThrowCompletionOr 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(int8bit);