fix: rounding errors for negative values in misc

Spendesk · Jun 14, 2022 · 984a2b1 · 984a2b1
1 parent d3a3f0a
commit 984a2b1
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Showing 2 changed files with 22 additions and 5 deletions.
diff --git a/src/operations/__tests__/misc.test.ts b/src/operations/__tests__/misc.test.ts
@@ -1,5 +1,6 @@
 import { sum, pow10, allocate as numberAllocate } from '../../utils/math';
 import { unsafeAdd } from '../binary';
+import { negate } from '../unary';
 
 import {
   integerDivide,
@@ -11,7 +12,7 @@ import {
   allocate,
   unsafeAllocate,
 } from '../misc';
-import { roundTowardsZero } from '../../roundings';
+import { roundHalfToEven, roundTowardsZero } from '../../roundings';
 
 describe('multiply()', () => {
   it('returns the same monetary value as unsafeMultiply()', () => {
@@ -138,7 +139,7 @@ describe('unsafeMultiply()', () => {
             unsafeMultiply(mv, factor, factorPrecision, roundTowardsZero),
           ).toHaveProperty(
             'amount',
-            Math.floor((mv.amount * factor) / pow10(factorPrecision)),
+            Math.trunc((mv.amount * factor) / pow10(factorPrecision)),
           );
         },
       ),
@@ -280,10 +281,26 @@ describe('unsafeIntegerDivide()', () => {
         fc.pre(divider !== 0);
         expect(
           unsafeIntegerDivide(mv, divider, roundTowardsZero),
-        ).toHaveProperty('amount', Math.floor(mv.amount / divider));
+        ).toHaveProperty('amount', Math.trunc(mv.amount / divider));
       }),
     );
   });
+  it('returns the same absolute monetary value when working with negative and positive values', () => {
+    fc.assert(
+      fc.property(
+        fc.monetaryValue(),
+        fc.integer(),
+        (mv, divider) => {
+          fc.pre(divider !== 0);
+          expect(
+            Math.abs(unsafeIntegerDivide(mv, divider, roundHalfToEven).amount),
+          ).toEqual(
+            Math.abs(unsafeIntegerDivide(negate(mv), divider, roundHalfToEven).amount),
+          )
+        },
+      ),
+    );
+  });
 });
 
 describe('divide()', () => {
@@ -451,7 +468,7 @@ describe('unsafeDivide()', () => {
             unsafeDivide(mv, divider, dividerPrecision, roundTowardsZero),
           ).toHaveProperty(
             'amount',
-            Math.floor((mv.amount * pow10(dividerPrecision)) / divider),
+            Math.trunc((mv.amount * pow10(dividerPrecision)) / divider),
           );
         },
       ),

diff --git a/src/operations/misc.ts b/src/operations/misc.ts
@@ -105,7 +105,7 @@ export function unsafeIntegerDivide<C extends string>(
   divider: number,
   roundingFunction: RoundingFunction = roundHalfToEven,
 ): MonetaryValue<C> {
-  const wholePart = Math.floor(monetaryValue.amount / divider);
+  const wholePart = Math.trunc(monetaryValue.amount / divider);
   const numerator = monetaryValue.amount % divider;
   return {
     amount: roundingFunction(wholePart, numerator, divider),