fix(js-core): improve accuracy of elapsedToString() when computing …

…both very large and very small units. (It is now accurate until the largest unit is about a quadrillion times the size of the smallest unit.)
simontonsoftware · Dec 4, 2021 · fa072cd · fa072cd
1 parent f29016a
commit fa072cd
Show file tree

Hide file tree

Showing 2 changed files with 26 additions and 3 deletions.
diff --git a/projects/js-core/src/lib/time/time-utils.spec.ts b/projects/js-core/src/lib/time/time-utils.spec.ts
@@ -83,6 +83,29 @@ describe('time-utils', () => {
         elapsedToString(1, ['ms'], { elapsedUnit: TimeUnit.Seconds }),
       ).toBe('1000 ms');
     });
+
+    it('is accurate with large gaps in units (production bug)', () => {
+      expect(
+        elapsedToString(convertTime(1, 'w', 'ns') - 1, ['w', 'ns'], {
+          elapsedUnit: TimeUnit.Nanoseconds,
+        }),
+      ).toBe('0 w 604_799_999_999_999 ns');
+      expect(
+        elapsedToString(convertTime(1, 'w', 'ns'), ['w', 'ns'], {
+          elapsedUnit: TimeUnit.Nanoseconds,
+        }),
+      ).toBe('1 w 0 ns');
+      expect(
+        elapsedToString(convertTime(1, 'mil', 'ms') - 1, ['mil', 'ms'], {
+          elapsedUnit: TimeUnit.Milliseconds,
+        }),
+      ).toBe('0 mil 31_535_999_999_999 ms');
+      expect(
+        elapsedToString(convertTime(1, 'mil', 'ms'), ['mil', 'ms'], {
+          elapsedUnit: TimeUnit.Milliseconds,
+        }),
+      ).toBe('1 mil 0 ms');
+    });
   });
 
   describe('convertTime()', () => {

diff --git a/projects/js-core/src/lib/time/time-utils.ts b/projects/js-core/src/lib/time/time-utils.ts
@@ -136,13 +136,13 @@ export function elapsedToString(
   let showZeros = showLeadingZeros;
   const tokens: Array<number | string> = [];
   units.forEach((unit, i) => {
-    const conversion = convertTime(1, elapsedUnit, unit);
-    const value = Math.floor(elapsed * conversion);
+    const conversion = convertTime(1, unit, elapsedUnit);
+    const value = Math.floor(elapsed / conversion);
     if (value > 0 || showZeros || i === units.length - 1) {
       tokens.push(value, unit);
       showZeros = true;
     }
-    elapsed -= value / conversion;
+    elapsed -= value * conversion;
   });
   return tokens.join(' ');
 }