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LibJS: Prevent i64 overflow when computing large NumberFormat exponents

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The largest exponents we compute are on the order of 10^21 (governed by
the maximumSignificantDigits option, which has a max value of 21). That
is too large to fit into the i64 we were using when multiplying this
exponent by the value to be formatted.

Instead, split up the logic to multiply that value by this exponent
based on the value's underlying type:

Number: Do not cast the result of pow() to an i64, and perform the
follow-up multiplication with doubles.

BigInt: Do not use pow(). Instead, compute the exponent as a BigInt
from the start, then perform the follow-up multiplication with that
BigInt.
This commit is contained in:
Timothy Flynn 2022-07-16 11:39:11 -04:00 • committed by Linus Groh
parent c367bcb5f8
commit 9e50f25ac4
2 changed files with 68 additions and 10 deletions
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28
Userland/Libraries/LibJS/Tests/builtins/Intl/NumberFormat/NumberFormat.prototype.format.js
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@ -78,6 +78,34 @@ describe("style=decimal", () => {
expect(en.format(12.3456)).toBe("12.3456");
expect(en.format(12.34567)).toBe("12.3457");
expect(en.format(12.34561)).toBe("12.3456");
expect(en.format(0.00000000000000000000000000000123)).toBe(
"0.000000000000000000000000000001230"
);
expect(en.format(-0.00000000000000000000000000000123)).toBe(
"-0.000000000000000000000000000001230"
);
expect(en.format(12344501000000000000000000000000000)).toBe(
"12,344,500,000,000,000,000,000,000,000,000,000"
);
expect(en.format(-12344501000000000000000000000000000)).toBe(
"-12,344,500,000,000,000,000,000,000,000,000,000"
);
expect(en.format(12344501000000000000000000000000000n)).toBe(
"12,344,500,000,000,000,000,000,000,000,000,000"
);
expect(en.format(-12344501000000000000000000000000000n)).toBe(
"-12,344,500,000,000,000,000,000,000,000,000,000"
);
const enLargeMaxSignificantDigits = new Intl.NumberFormat("en", {
minimumSignificantDigits: 4,
maximumSignificantDigits: 21,
});
expect(enLargeMaxSignificantDigits.format(1)).toBe("1.000");
expect(enLargeMaxSignificantDigits.format(1n)).toBe("1.000");
expect(enLargeMaxSignificantDigits.format(123456789123456789123456789123456789n)).toBe(
"123,456,789,123,456,789,123,000,000,000,000,000"
);
const ar = new Intl.NumberFormat("ar", {
minimumSignificantDigits: 4,