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fix: speedup dayOfWeek routine in date #3033

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fix: speedup dayOfWeek routine in date #3033

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10c288b
fix: speedup dayOfWeek
MaxGraey Jul 8, 2026
34f5d5d
refaxctor
MaxGraey Jul 9, 2026
9893245
refactor more (nfc)
MaxGraey Jul 9, 2026
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30 changes: 15 additions & 15 deletions std/assembly/date.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -3,15 +3,14 @@ import { Date as Date_binding } from "./bindings/dom";

// @ts-ignore: decorator
@inline const
MILLIS_LIMIT = 8640000000000000,
MILLIS_PER_DAY = 1000 * 60 * 60 * 24,
MILLIS_PER_HOUR = 1000 * 60 * 60,
MILLIS_PER_MINUTE = 1000 * 60,
MILLIS_PER_SECOND = 1000,

YEARS_PER_EPOCH = 400,
DAYS_PER_EPOCH = 146097,
EPOCH_OFFSET = 719468, // Jan 1, 1970
MILLIS_LIMIT = 8640000000000000;
YEARS_PER_EPOCH = 400,
DAYS_PER_EPOCH = 146097, // 400 * 365 + 400 / 4 - 400 / 100 + 1
EPOCH_OFFSET = 719468; // Jan 1, 1970

// ymdFromEpochDays returns values via globals to avoid allocations
// @ts-ignore: decorator
Expand Down Expand Up @@ -62,7 +61,7 @@ export class Date {
let timeString: string;
dateString = dateTimeString.substring(0, posT);
timeString = dateTimeString.substring(posT + 1);

// might end with an offset ("Z", "+05:30", "-08:00", etc.)
for (let i = timeString.length - 1; i >= 0; i--) {
let c = timeString.charCodeAt(i);
Expand All @@ -82,8 +81,8 @@ export class Date {
} else {
let offsetHours = i32.parse(timeString.substring(i + 1));
offsetMs = offsetHours * MILLIS_PER_HOUR;
}
}

if (c == 45) offsetMs = -offsetMs; // negative offset
timeString = timeString.substring(0, i);
break;
Expand Down Expand Up @@ -347,11 +346,11 @@ function dateFromEpoch(ms: i64): i32 {
}

// http://howardhinnant.github.io/date_algorithms.html#days_from_civil
function daysSinceEpoch(y: i32, m: i32, d: i32): i64 {
y -= i32(m <= 2);
let era = <u32>floorDiv(y, YEARS_PER_EPOCH);
let yoe = <u32>y - era * YEARS_PER_EPOCH; // [0, 399]
let doy = <u32>(153 * (m + (m > 2 ? -3 : 9)) + 2) / 5 + d - 1; // [0, 365]
function daysSinceEpoch(year: i32, month: i32, day: i32): i64 {
year -= i32(month <= 2);
let era = <u32>floorDiv(year, YEARS_PER_EPOCH);
let yoe = <u32>year - era * YEARS_PER_EPOCH; // [0, 399]
let doy = <u32>(153 * (month + (month > 2 ? -3 : 9)) + 2) / 5 + day - 1; // [0, 365]
let doe = yoe * 365 + yoe / 4 - yoe / 100 + doy; // [0, 146096]
return <i64><i32>(era * 146097 + doe - EPOCH_OFFSET);
}
Expand All @@ -360,8 +359,9 @@ function daysSinceEpoch(y: i32, m: i32, d: i32): i64 {
function dayOfWeek(year: i32, month: i32, day: i32): i32 {
const tab = memory.data<u8>([0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4]);

year -= i32(month < 3);
year += floorDiv(year, 4) - floorDiv(year, 100) + floorDiv(year, YEARS_PER_EPOCH);
year -= i32(month <= 2);
const cent = floorDiv(year >> 2, 100 >> 2);
year += (year >> 2) - cent + (cent >> 2);
month = <i32>load<u8>(tab + month - 1);
return euclidRem(year + month + day, 7);
}
Expand Down
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