fix: ClassCastException calling divideAndRemainder

src/commonTest/kotlin/org/gciatto/kt/math/TestIntegers.kt

@@ -74,6 +74,65 @@ class TestIntegers {
         assertEquals("-9223372036854775818", (BigInteger.of(Long.MIN_VALUE) - BigInteger.TEN).toString())
     }
 
+    @Test
+    fun testDivideAndRemainder() {
+        fun assertArrayContains(
+            expectedQuotient: BigInteger,
+            expectedRemainder: BigInteger,
+            actualResult: Array<out BigInteger>
+        ) {
+            assertEquals(2, actualResult.size)
+            assertBigIntegersAreEquals(expectedQuotient, actualResult[0])
+            assertBigIntegersAreEquals(expectedRemainder, actualResult[1])
+        }
+
+        fun doTest(
+            dividendInt: Int,
+            divisorInt: Int,
+            expectedQuotientInt: Int,
+            expectedRemainderInt: Int
+        ) {
+            val divisorLong = divisorInt.toLong()
+            val dividend = BigInteger.of(dividendInt)
+            val divisor = BigInteger.of(divisorInt)
+            val expectedQuotient = BigInteger.of(expectedQuotientInt)
+            val expectedRemainder = BigInteger.of(expectedRemainderInt)
+
+            // int overloads
+            assertBigIntegersAreEquals(expectedQuotient, dividend.div(divisorInt))
+            assertBigIntegersAreEquals(expectedRemainder, dividend.rem(divisorInt))
+            assertBigIntegersAreEquals(expectedRemainder, dividend.remainder(divisorInt))
+            assertArrayContains(expectedQuotient, expectedRemainder, dividend.divideAndRemainder(divisorInt))
+
+            // long overloads
+            assertBigIntegersAreEquals(expectedQuotient, dividend.div(divisorLong))
+            assertBigIntegersAreEquals(expectedRemainder, dividend.rem(divisorLong))
+            assertBigIntegersAreEquals(expectedRemainder, dividend.remainder(divisorLong))
+            assertArrayContains(expectedQuotient, expectedRemainder, dividend.divideAndRemainder(divisorLong))
+
+            // BigInteger overloads
+            assertBigIntegersAreEquals(expectedQuotient, dividend.div(divisor))
+            assertBigIntegersAreEquals(expectedRemainder, dividend.rem(divisor))
+            assertBigIntegersAreEquals(expectedRemainder, dividend.remainder(divisor))
+            assertArrayContains(expectedQuotient, expectedRemainder, dividend.divideAndRemainder(divisor))
+        }
+
+        doTest(0, 3, 0, 0)
+        doTest(0, -3, 0, 0)
+        doTest(1, 3, 0, 1)
+        doTest(1, -3, 0, 1)
+        doTest(-1, 3, 0, -1)
+        doTest(-1, -3, 0, -1)
+        doTest(6, 2, 3, 0)
+        doTest(6, -2, -3, 0)
+        doTest(-6, -2, 3, 0)
+        doTest(-6, 2, -3, 0)
+        doTest(7, 2, 3, 1)
+        doTest(7, -2, -3, 1)
+        doTest(-7, -2, 3, -1)
+        doTest(-7, 2, -3, -1)
+    }
+
     @Test
     fun testDecimalParsing() {
         assertEquals(0, BigInteger.of("0").toInt())

src/jvmMain/kotlin/org/gciatto/kt/math/JavaBigIntegerAdapter.kt

@@ -21,13 +21,18 @@ internal class JavaBigIntegerAdapter(val value: JavaBigInteger) : BigInteger {
     }
 
     private inline fun adaptAll(
-        other: BigInteger,
+        other: JavaBigIntegerAdapter,
         f: (JavaBigInteger) -> Array<JavaBigInteger>,
     ): Array<out JavaBigIntegerAdapter> {
-        val javaInts = f(other.castTo())
+        val javaInts = f(other.value)
         return Array(javaInts.size) { index -> adapt { javaInts[index] } }
     }
 
+    private inline fun adaptAll(
+        other: BigInteger,
+        f: (JavaBigInteger) -> Array<JavaBigInteger>,
+    ): Array<out JavaBigIntegerAdapter> = adaptAll(other.castTo(), f)
+
     override val absoluteValue: BigInteger
         get() = adapt { value.abs() }
 
@@ -54,8 +59,8 @@ internal class JavaBigIntegerAdapter(val value: JavaBigInteger) : BigInteger {
     override fun div(other: BigInteger): BigInteger = adapt(other) { value.divide(it) }
 
     override fun divideAndRemainder(other: BigInteger): Array<out BigInteger> =
-        adaptAll(other) {
-            value.divideAndRemainder(it)
+        adaptAll(other) { otherJava: JavaBigInteger ->
+            value.divideAndRemainder(otherJava)
         }
 
     override fun remainder(other: BigInteger): BigInteger = adapt(other) { value.remainder(it) }