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Normative: Limit time portion of durations to <2⁵³ seconds
In order to avoid unbounded integer arithmetic, we place an upper bound on the total of the time portion of a duration (days through nanoseconds). For the purpose of determining the limits, days are always 24 hours, even if a calendar day may be a different number of hours relative to a particular ZonedDateTime. It's now no longer possible to make Duration.prototype.total() come up with an infinite result; removing the loops in UnbalanceDurationRelative made it so that the duration's calendar units must be able to be added to a relativeTo date without overflowing, and this change makes it so that the duration's time units are too small to overflow to infinity either.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,32 @@ | ||
| const MathAbs = Math.abs; | ||
| const MathLog10 = Math.log10; | ||
| const MathSign = Math.sign; | ||
| const MathTrunc = Math.trunc; | ||
| const NumberParseInt = Number.parseInt; | ||
| const NumberPrototypeToPrecision = Number.prototype.toPrecision; | ||
| const StringPrototypeSlice = String.prototype.slice; | ||
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| import Call from 'es-abstract/2022/Call.js'; | ||
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| // Computes trunc(x / 10**p) and x % 10**p, returning { div, mod }, with | ||
| // precision loss only once in the quotient, by string manipulation. If the | ||
| // quotient and remainder are safe integers, then they are exact. x must be an | ||
| // integer. p must be a non-negative integer. Both div and mod have the sign of | ||
| // x. | ||
| export function TruncatingDivModByPowerOf10(x, p) { | ||
| if (x === 0) return { div: x, mod: x }; // preserves signed zero | ||
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| const sign = MathSign(x); | ||
| x = MathAbs(x); | ||
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| const xDigits = MathTrunc(1 + MathLog10(x)); | ||
| if (p >= xDigits) return { div: sign * 0, mod: sign * x }; | ||
| if (p === 0) return { div: sign * x, mod: sign * 0 }; | ||
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| // would perform nearest rounding if x was not an integer: | ||
| const xStr = Call(NumberPrototypeToPrecision, x, [xDigits]); | ||
| const div = sign * NumberParseInt(Call(StringPrototypeSlice, xStr, [0, xDigits - p]), 10); | ||
| const mod = sign * NumberParseInt(Call(StringPrototypeSlice, xStr, [xDigits - p]), 10); | ||
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| return { div, mod }; | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,69 @@ | ||
| import Demitasse from '@pipobscure/demitasse'; | ||
| const { describe, it, report } = Demitasse; | ||
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| import Pretty from '@pipobscure/demitasse-pretty'; | ||
| const { reporter } = Pretty; | ||
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| import { strict as assert } from 'assert'; | ||
| const { deepEqual } = assert; | ||
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| import { TruncatingDivModByPowerOf10 as div } from '../lib/math.mjs'; | ||
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| describe('Math', () => { | ||
| describe('TruncatingDivModByPowerOf10', () => { | ||
| it('12345/10**0 = 12345, 0', () => deepEqual(div(12345, 0), { div: 12345, mod: 0 })); | ||
| it('12345/10**1 = 1234, 5', () => deepEqual(div(12345, 1), { div: 1234, mod: 5 })); | ||
| it('12345/10**2 = 123, 45', () => deepEqual(div(12345, 2), { div: 123, mod: 45 })); | ||
| it('12345/10**3 = 12, 345', () => deepEqual(div(12345, 3), { div: 12, mod: 345 })); | ||
| it('12345/10**4 = 1, 2345', () => deepEqual(div(12345, 4), { div: 1, mod: 2345 })); | ||
| it('12345/10**5 = 0, 12345', () => deepEqual(div(12345, 5), { div: 0, mod: 12345 })); | ||
| it('12345/10**6 = 0, 12345', () => deepEqual(div(12345, 6), { div: 0, mod: 12345 })); | ||
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| it('-12345/10**0 = -12345, -0', () => deepEqual(div(-12345, 0), { div: -12345, mod: -0 })); | ||
| it('-12345/10**1 = -1234, -5', () => deepEqual(div(-12345, 1), { div: -1234, mod: -5 })); | ||
| it('-12345/10**2 = -123, -45', () => deepEqual(div(-12345, 2), { div: -123, mod: -45 })); | ||
| it('-12345/10**3 = -12, -345', () => deepEqual(div(-12345, 3), { div: -12, mod: -345 })); | ||
| it('-12345/10**4 = -1, -2345', () => deepEqual(div(-12345, 4), { div: -1, mod: -2345 })); | ||
| it('-12345/10**5 = -0, -12345', () => deepEqual(div(-12345, 5), { div: -0, mod: -12345 })); | ||
| it('-12345/10**6 = -0, -12345', () => deepEqual(div(-12345, 6), { div: -0, mod: -12345 })); | ||
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| it('0/10**27 = 0, 0', () => deepEqual(div(0, 27), { div: 0, mod: 0 })); | ||
| it('-0/10**27 = -0, -0', () => deepEqual(div(-0, 27), { div: -0, mod: -0 })); | ||
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| it('1001/10**3 = 1, 1', () => deepEqual(div(1001, 3), { div: 1, mod: 1 })); | ||
| it('-1001/10**3 = -1, -1', () => deepEqual(div(-1001, 3), { div: -1, mod: -1 })); | ||
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| it('4019125567429664768/10**3 = 4019125567429664, 768', () => | ||
| deepEqual(div(4019125567429664768, 3), { div: 4019125567429664, mod: 768 })); | ||
| it('-4019125567429664768/10**3 = -4019125567429664, -768', () => | ||
| deepEqual(div(-4019125567429664768, 3), { div: -4019125567429664, mod: -768 })); | ||
| it('3294477463410151260160/10**6 = 3294477463410151, 260160', () => | ||
| deepEqual(div(3294477463410151260160, 6), { div: 3294477463410151, mod: 260160 })); | ||
| it('-3294477463410151260160/10**6 = -3294477463410151, -260160', () => | ||
| deepEqual(div(-3294477463410151260160, 6), { div: -3294477463410151, mod: -260160 })); | ||
| it('7770017954545649059889152/10**9 = 7770017954545649, 59889152', () => | ||
| deepEqual(div(7770017954545649059889152, 9), { div: 7770017954545649, mod: 59889152 })); | ||
| it('-7770017954545649059889152/-10**9 = -7770017954545649, -59889152', () => | ||
| deepEqual(div(-7770017954545649059889152, 9), { div: -7770017954545649, mod: -59889152 })); | ||
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| // Largest/smallest representable float that will result in a safe quotient, | ||
| // for each of the divisors 10**3, 10**6, 10**9 | ||
| it('9007199254740990976/10**3 = MAX_SAFE_INTEGER-1, 976', () => | ||
| deepEqual(div(9007199254740990976, 3), { div: Number.MAX_SAFE_INTEGER - 1, mod: 976 })); | ||
| it('-9007199254740990976/10**3 = -MAX_SAFE_INTEGER+1, -976', () => | ||
| deepEqual(div(-9007199254740990976, 3), { div: -Number.MAX_SAFE_INTEGER + 1, mod: -976 })); | ||
| it('9007199254740990951424/10**6 = MAX_SAFE_INTEGER-1, 951424', () => | ||
| deepEqual(div(9007199254740990951424, 6), { div: Number.MAX_SAFE_INTEGER - 1, mod: 951424 })); | ||
| it('-9007199254740990951424/10**6 = -MAX_SAFE_INTEGER+1, -951424', () => | ||
| deepEqual(div(-9007199254740990951424, 6), { div: -Number.MAX_SAFE_INTEGER + 1, mod: -951424 })); | ||
| it('9007199254740990926258176/10**9 = MAX_SAFE_INTEGER-1, 926258176', () => | ||
| deepEqual(div(9007199254740990926258176, 9), { div: Number.MAX_SAFE_INTEGER - 1, mod: 926258176 })); | ||
| it('-9007199254740990926258176/10**9 = -MAX_SAFE_INTEGER+1, -926258176', () => | ||
| deepEqual(div(-9007199254740990926258176, 9), { div: -Number.MAX_SAFE_INTEGER + 1, mod: -926258176 })); | ||
| }); | ||
| }); | ||
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| import { normalize } from 'path'; | ||
| if (normalize(import.meta.url.slice(8)) === normalize(process.argv[1])) { | ||
| report(reporter).then((failed) => process.exit(failed ? 1 : 0)); | ||
| } |
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