fix #3087: extend function mod with support for negative divisors i…

…n when using `BigNumber` or `Fraction`

HISTORY.md

@@ -1,6 +1,12 @@
 # History
 
 
+# unpublished changes since 12.0.0
+
+- Fix #3087: extend function `mod` with support for negative divisors in when
+  using `BigNumber` or `Fraction`.
+
+
 # 2023-10-26, 12.0.0
 
 Breaking changes:

src/function/arithmetic/mod.js

@@ -69,17 +69,11 @@ export const createMod = /* #__PURE__ */ factory(name, dependencies, ({ typed, c
       'number, number': _modNumber,
 
       'BigNumber, BigNumber': function (x, y) {
-        if (y.isNeg()) {
-          throw new Error('Cannot calculate mod for a negative divisor')
-        } return y.isZero() ? x : x.mod(y)
+        return y.isZero() ? x : x.sub(y.mul(floor(x.div(y))))
       },
 
       'Fraction, Fraction': function (x, y) {
-        if (y.compare(0) < 0) {
-          throw new Error('Cannot calculate mod for a negative divisor')
-        }
-        // Workaround suggested in Fraction.js library to calculate correct modulo for negative dividend
-        return x.compare(0) >= 0 ? x.mod(y) : x.mod(y).add(y).mod(y)
+        return y.equals(0) ? x : x.sub(y.mul(floor(x.div(y))))
       }
     },
     matrixAlgorithmSuite({

test/unit-tests/function/arithmetic/mod.test.js

@@ -73,8 +73,8 @@ describe('mod', function () {
     assert.deepStrictEqual(mod(bignumber(-5), bignumber(3)), bignumber(1))
   })
 
-  it('should throw an error if the divisor in modulus of bignumbers is negative', function () {
-    assert.throws(function () { mod(bignumber(10), bignumber(-4)) })
+  it('should calculate the modulus of bignumbers for a negative divisor', function () {
+    assert.deepStrictEqual(mod(bignumber(10), bignumber(-4)), bignumber(-2))
   })
 
   it('should calculate the modulus of mixed numbers and bignumbers', function () {
@@ -126,8 +126,8 @@ describe('mod', function () {
     assert.strictEqual(mod(math.fraction(-5), math.fraction(3)).toString(), '1')
   })
 
-  it('should throw an error if the divosor in modulus of fractions is negative', function () {
-    assert.throws(function () { mod(math.fraction(10), math.fraction(-4)) })
+  it('should calculate the modulus of fractions for a negative divisor', function () {
+    assert.strictEqual(mod(math.fraction(10), math.fraction(-4)).toString(), '-2')
   })
 
   it('should calculate modulus of mixed fractions and numbers', function () {