Refactor stringify methods of Date (#2398)

Author: MaxGraey

std/assembly/date.ts

@@ -169,125 +169,98 @@ export class Date {
 
   setUTCDate(day: i32): void {
     if (this.day == day) return;
-    var ms = euclidRem(this.epochMillis, MILLIS_PER_DAY);
-    this.setTime(i64(daysSinceEpoch(this.year, this.month, day)) * MILLIS_PER_DAY + ms);
+    this.setTime(join(this.year, this.month, day, this.epochMillis));
   }
 
   setUTCMonth(month: i32, day: i32 = this.day): void {
     if (this.month == month + 1) return;
-    var ms = euclidRem(this.epochMillis, MILLIS_PER_DAY);
-    this.setTime(i64(daysSinceEpoch(this.year, month + 1, day)) * MILLIS_PER_DAY + ms);
+    this.setTime(join(this.year, month + 1, day, this.epochMillis));
   }
 
   setUTCFullYear(year: i32): void {
     if (this.year == year) return;
-    var ms = euclidRem(this.epochMillis, MILLIS_PER_DAY);
-    this.setTime(i64(daysSinceEpoch(year, this.month, this.day)) * MILLIS_PER_DAY + ms);
+    this.setTime(join(year, this.month, this.day, this.epochMillis));
   }
 
   toISOString(): string {
     // TODO: add more low-level helper which combine toString and padStart without extra allocation
-    var yearStr: string;
-    var year = this.year;
-    var isNeg = year < 0;
-    if (isNeg || year >= 10000) {
-      yearStr = (isNeg ? "-" : "+") + abs(year).toString().padStart(6, "0");
-    } else {
-      yearStr = year.toString().padStart(4, "0");
-    }
 
-    return (
-      yearStr +
-      "-" +
-      this.month.toString().padStart(2, "0") +
-      "-" +
-      this.day.toString().padStart(2, "0") +
-      "T" +
-      this.getUTCHours().toString().padStart(2, "0") +
-      ":" +
-      this.getUTCMinutes().toString().padStart(2, "0") +
-      ":" +
-      this.getUTCSeconds().toString().padStart(2, "0") +
-      "." +
-      this.getUTCMilliseconds().toString().padStart(3, "0") +
-      "Z"
-    );
+    var yr = this.year;
+    var isNeg = yr < 0;
+    var year = (isNeg || yr >= 10000)
+      ? (isNeg ? "-" : "+") + stringify(abs(yr), 6)
+      : stringify(yr, 4);
+    var month = stringify(this.month, 2);
+    var day = stringify(this.day);
+    var hours = stringify(this.getUTCHours());
+    var mins = stringify(this.getUTCMinutes());
+    var secs = stringify(this.getUTCSeconds());
+    var ms = stringify(this.getUTCMilliseconds(), 3);
+
+    return `${year}-${month}-${day}T${hours}:${mins}:${secs}.${ms}Z`;
   }
 
   toUTCString(): string {
-    const weeks: StaticArray<string> = [
-      "Sun, ", "Mon, ", "Tue, ", "Wed, ", "Thu, ", "Fri, ", "Sat, "
-    ];
-
-    const months: StaticArray<string> = [
-      " Jan ", " Feb ", " Mar ", " Apr ", " May ", " Jun ",
-      " Jul ", " Aug ", " Sep ", " Oct ", " Nov ", " Dec "
-    ];
+    const
+      weeks: StaticArray<string> = [
+        "Sun, ", "Mon, ", "Tue, ", "Wed, ", "Thu, ", "Fri, ", "Sat, "
+      ],
+      months: StaticArray<string> = [
+        " Jan ", " Feb ", " Mar ", " Apr ", " May ", " Jun ",
+        " Jul ", " Aug ", " Sep ", " Oct ", " Nov ", " Dec "
+      ];
 
     var mo = this.month;
     var da = this.day;
     var yr = this.year;
     var wd = dayOfWeek(yr, mo, da);
-    var year = abs(yr).toString().padStart(4, "0");
-    if (yr < 0) year = "-" + year;
-
-    return (
-      unchecked(weeks[wd]) +
-      da.toString().padStart(2, "0") +
-      unchecked(months[mo - 1]) +
-      year +
-      " " +
-      this.getUTCHours().toString().padStart(2, "0") +
-      ":" +
-      this.getUTCMinutes().toString().padStart(2, "0") +
-      ":" +
-      this.getUTCSeconds().toString().padStart(2, "0") +
-      " GMT"
-    );
+    var year = stringify(abs(yr), 4);
+    var month = unchecked(months[mo - 1]);
+    var week = unchecked(weeks[wd]);
+    var day = stringify(da);
+    var hours = stringify(this.getUTCHours());
+    var mins = stringify(this.getUTCMinutes());
+    var secs = stringify(this.getUTCSeconds());
+
+    return `${week}${day}${month}${yr < 0 ? "-" : ""}${year} ${hours}:${mins}:${secs} GMT`;
   }
 
   toDateString(): string {
     // TODO: use u64 static data instead 4 chars
     // also use stream itoa variants.
-    const weeks: StaticArray<string> = [
-      "Sun ", "Mon ", "Tue ", "Wed ", "Thu ", "Fri ", "Sat "
-    ];
-
-    const months: StaticArray<string> = [
-      "Jan ", "Feb ", "Mar ", "Apr ", "May ", "Jun ",
-      "Jul ", "Aug ", "Sep ", "Oct ", "Nov ", "Dec "
-    ];
+    const
+      weeks: StaticArray<string> = [
+        "Sun ", "Mon ", "Tue ", "Wed ", "Thu ", "Fri ", "Sat "
+      ],
+      months: StaticArray<string> = [
+        "Jan ", "Feb ", "Mar ", "Apr ", "May ", "Jun ",
+        "Jul ", "Aug ", "Sep ", "Oct ", "Nov ", "Dec "
+      ];
 
     var mo = this.month;
     var da = this.day;
     var yr = this.year;
     var wd = dayOfWeek(yr, mo, da);
-    var year = abs(yr).toString().padStart(4, "0");
-    if (yr < 0) year = "-" + year;
-
-    return (
-      unchecked(weeks[wd]) +
-      unchecked(months[mo - 1]) +
-      da.toString().padStart(2, "0") +
-      " " + year
-    );
+    var year = stringify(abs(yr), 4);
+    var month = unchecked(months[mo - 1]);
+    var week = unchecked(weeks[wd]);
+    var day = stringify(da);
+
+    return `${week}${month}${day}${yr < 0 ? " -" : " "}${year}`;
   }
 
   // Note: it uses UTC time instead local time (without timezone offset)
   toTimeString(): string {
+    var hours = stringify(this.getUTCHours());
+    var mins = stringify(this.getUTCMinutes());
+    var secs = stringify(this.getUTCSeconds());
     // TODO: add timezone
-    return (
-      this.getUTCHours().toString().padStart(2, "0") +
-      ":" +
-      this.getUTCMinutes().toString().padStart(2, "0") +
-      ":" +
-      this.getUTCSeconds().toString().padStart(2, "0")
-    );
+    return `${hours}:${mins}:${secs}`;
   }
 
   // Note: it uses UTC datetime instead local datetime (without timezone offset)
   toString(): string {
-    return this.toDateString() + " " + this.toTimeString();
+    return `${this.toDateString()} ${this.toTimeString()}`;
   }
 }
 
@@ -301,7 +274,7 @@ function epochMillis(
   milliseconds: i32
 ): i64 {
   return (
-    i64(daysSinceEpoch(year, month, day)) * MILLIS_PER_DAY +
+    daysSinceEpoch(year, month, day) * MILLIS_PER_DAY +
     hour * MILLIS_PER_HOUR +
     minute * MILLIS_PER_MINUTE +
     second * MILLIS_PER_SECOND +
@@ -343,13 +316,13 @@ function dateFromEpoch(ms: i64): i32 {
 }
 
 // http://howardhinnant.github.io/date_algorithms.html#days_from_civil
-function daysSinceEpoch(y: i32, m: i32, d: i32): i32 {
+function daysSinceEpoch(y: i32, m: i32, d: i32): i64 {
   y -= i32(m <= 2);
   var era = <u32>floorDiv(y, YEARS_PER_EPOCH);
   var yoe = <u32>y - era * YEARS_PER_EPOCH; // [0, 399]
   var doy = <u32>(153 * (m + (m > 2 ? -3 : 9)) + 2) / 5 + d - 1; // [0, 365]
   var doe = yoe * 365 + yoe / 4 - yoe / 100 + doy; // [0, 146096]
-  return era * 146097 + doe - EPOCH_OFFSET;
+  return <i64><i32>(era * 146097 + doe - EPOCH_OFFSET);
 }
 
 // TomohikoSakamoto algorithm from https://en.wikipedia.org/wiki/Determination_of_the_day_of_the_week
@@ -361,3 +334,11 @@ function dayOfWeek(year: i32, month: i32, day: i32): i32 {
   month = <i32>load<u8>(tab + month - 1);
   return euclidRem(year + month + day, 7);
 }
+
+function stringify(value: i32, padding: i32 = 2): string {
+  return value.toString().padStart(padding, "0");
+}
+
+function join(year: i32, month: i32, day: i32, ms: i64): i64 {
+  return daysSinceEpoch(year, month, day) * MILLIS_PER_DAY + euclidRem(ms, MILLIS_PER_DAY);
+}