0ct0pu5/ladybird
1
0
Fork 0
mirror of https://github.com/LadybirdBrowser/ladybird.git synced 2024-12-04 13:30:31 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions 7

LibJS: Support large number of decimals in Number.prototype.toFixed

Browse source 
The spec asks us to perform some calculations that quickly exceed an
`u64`, but instead of jumping through hoops we can rely on our AK
implementation of floating point formatting to come up with the
correctly rounded result.

Note that most other JS engines seem to diverge from the spec as well
and fall back to a generic dtoa path.
This commit is contained in:
Jelle Raaijmakers 2023-10-15 17:02:21 +02:00 committed by Tim Flynn
parent b015926f8e
commit c58193bafa
Notes: sideshowbarker 2024-07-17 02:35:27 +09:00 
Author: https://github.com/gmta
Commit: https://github.com/SerenityOS/serenity/commit/c58193bafa
Pull-request: https://github.com/SerenityOS/serenity/pull/21454
2 changed files with 35 additions and 34 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

54
Userland/Libraries/LibJS/Runtime/NumberPrototype.cpp
View file

@ -232,44 +232,30 @@ JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_fixed)
number = -number;
// 10. If x ≥ 10^21, then
if (fabs(number) >= 1e+21)
// a. Let m be ! ToString(𝔽(x)).
if (number >= 1e+21)
return PrimitiveString::create(vm, MUST(number_value.to_deprecated_string(vm)));
// 11. Else,
// a. Let n be an integer for which n / (10^f) - x is as close to zero as possible. If there are two such n, pick the larger n.
// FIXME: This breaks down with values of `fraction_digits` > 23
auto n = round(pow(10.0f, fraction_digits) * number);
// b. If n = 0, let m be the String "0". Otherwise, let m be the String value consisting of the digits of the decimal representation of n (in order, with no leading zeroes).
auto m = (n == 0 ? "0" : DeprecatedString::formatted("{}", n));
// c. If f ≠ 0, then
if (fraction_digits != 0) {
// i. Let k be the length of m.
auto k = static_cast<size_t>(m.length());
// ii. If k ≤ f, then
if (k <= fraction_digits) {
// 1. Let z be the String value consisting of f + 1 - k occurrences of the code unit 0x0030 (DIGIT ZERO).
auto z = DeprecatedString::repeated('0', fraction_digits + 1 - k);
// 2. Set m to the string-concatenation of z and m.
m = DeprecatedString::formatted("{}{}", z, m);
// 3. Set k to f + 1.
k = fraction_digits + 1;
}
// iii. Let a be the first k - f code units of m.
// iv. Let b be the other f code units of m.
// v. Set m to the string-concatenation of a, ".", and b.
m = DeprecatedString::formatted("{}.{}",
m.substring_view(0, k - fraction_digits),
m.substring_view(k - fraction_digits, fraction_digits));
}
// a. Let n be an integer for which n / (10^f) - x is as close to zero as possible. If there are two such n, pick the larger n.
// b. If n = 0, let m be the String "0". Otherwise, let m be the String value consisting of the digits of the decimal representation of n (in order, with no leading zeroes).
// c. If f ≠ 0, then
// i. Let k be the length of m.
// ii. If k ≤ f, then
// 1. Let z be the String value consisting of f + 1 - k occurrences of the code unit 0x0030 (DIGIT ZERO).
// 2. Set m to the string-concatenation of z and m.
// 3. Set k to f + 1.
// iii. Let a be the first k - f code units of m.
// iv. Let b be the other f code units of m.
// v. Set m to the string-concatenation of a, ".", and b.
// 12. Return the string-concatenation of s and m.
return PrimitiveString::create(vm, DeprecatedString::formatted("{}{}", s, m));
// NOTE: the above steps are effectively trying to create a formatted string of the
// `number` double. Instead of generating a huge, unwieldy `n`, we format
// the double using our existing formatting code.
auto number_format_string = DeprecatedString::formatted("{{}}{{:.{}f}}", fraction_digits);
return PrimitiveString::create(vm, DeprecatedString::formatted(number_format_string, s, number));
}
// 19.2.1 Number.prototype.toLocaleString ( [ locales [ , options ] ] ), https://tc39.es/ecma402/#sup-number.prototype.tolocalestring

15
Userland/Libraries/LibJS/Tests/builtins/Number/Number.prototype.toFixed.js
View file

@ -31,6 +31,21 @@ describe("correct behavior", () => {
});
});
describe("large number of digits", () => {
test("maximum", () => {
expect((1).toFixed(100)).toBe(
"1.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
);
expect((-3).toFixed(100)).toBe(
"-3.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
);
});
test("fractional values", () => {
expect((1.5).toFixed(30)).toBe("1.500000000000000000000000000000");
});
});
describe("errors", () => {
test("must be called with numeric |this|", () => {
[true, [], {}, Symbol("foo"), "bar", 1n].forEach(value => {