feat(core): implement gcd & lcm

Author: ObserverOfTime

kbigint/src/androidMain/kotlin/io/github/observeroftime/kbigint/KBigInt.kt

@@ -67,6 +67,14 @@ actual class KBigInt private constructor(private var value: BigInteger) : Compar
 
     actual infix fun xor(other: KBigInt) = KBigInt(value xor other.value)
 
+    actual fun gcd(other: KBigInt) = KBigInt(value.gcd(other.value))
+
+    actual fun lcm(other: KBigInt): KBigInt {
+        val a = value.abs()
+        val b = other.value.abs()
+        return KBigInt(a * b / a.gcd(b))
+    }
+
     @JvmName("shiftLeft")
     actual infix fun shl(n: Int) = KBigInt(value shl n)
 

kbigint/src/androidUnitTest/kotlin/io/github/observeroftime/kbigint/KBigIntTest.kt

@@ -75,6 +75,15 @@ actual class KBigIntTest {
         assertEquals(KBigInt(2147483649L), -long.inv())
     }
 
+    @Test
+    actual fun testGcdLcm() {
+        val a = KBigInt(-4)
+        val b = KBigInt(10)
+
+        assertEquals(KBigInt(2), a.gcd(b))
+        assertEquals(KBigInt(20), a.lcm(b))
+    }
+
     @Test
     actual fun testPow() {
         assertEquals(KBigInt("4611686018427387904"), long pow 2)

kbigint/src/commonMain/kotlin/io/github/observeroftime/kbigint/KBigInt.kt

@@ -62,6 +62,12 @@ expect class KBigInt : Comparable<KBigInt> {
     /** Perform a bitwise `XOR` operation. */
     infix fun xor(other: KBigInt): KBigInt
 
+    /** Find the (absolute) Greatest Common Divisor of two values. */
+    fun gcd(other: KBigInt): KBigInt
+
+    /** Find the (absolute) Least Common Multiplier of two values. */
+    fun lcm(other: KBigInt): KBigInt
+
     /** Shift the value to the left by [n]. */
     infix fun shl(n: Int): KBigInt
 

kbigint/src/commonTest/kotlin/io/github/observeroftime/kbigint/KBigIntTest.kt

@@ -12,6 +12,7 @@ expect class KBigIntTest {
     fun testBitOps()
     fun testShifts()
     fun testInvert()
+    fun testGcdLcm()
     fun testPow()
     fun testSqrt()
     fun testAbs()

kbigint/src/javascript/kbigint-utils.mjs

@@ -69,6 +69,18 @@ export function cmp(a, b) {
     return a === b ? 0 : a < b ? -1 : 1;
 }
 
+/**
+ * Find the Greatest Common Divisor
+ *
+ * @param {bigint} a
+ * @param {bigint} b
+ * @returns {bigint}
+ */
+export function gcd(a, b) {
+    if (b === 0n) return a;
+    return gcd(b, a % b);
+}
+
 /**
  * Raise the value to the `n`-th power.
  *

kbigint/src/jsMain/kotlin/io/github/observeroftime/kbigint/KBigInt.kt

@@ -97,6 +97,19 @@ actual class KBigInt private constructor(@JsExternalArgument private var value:
         return KBigInt(js("a ^ b").unsafeCast<BigInt>())
     }
 
+    actual fun gcd(other: KBigInt): KBigInt {
+        val gcd = KBigIntUtils.gcd(value, other.value)
+        return KBigInt(KBigIntUtils.abs(gcd))
+    }
+
+    actual fun lcm(other: KBigInt): KBigInt {
+        val a = this.value
+        val b = other.value
+        val c = KBigIntUtils.gcd(a, b)
+        val lcm = js("a * b / c").unsafeCast<BigInt>()
+        return KBigInt(KBigIntUtils.abs(lcm))
+    }
+
     @JsName("shiftLeft")
     actual infix fun shl(n: Int): KBigInt {
         val a = this.value

kbigint/src/jsMain/kotlin/io/github/observeroftime/kbigint/KBigIntUtils.kt

@@ -15,6 +15,7 @@ internal external object KBigIntUtils {
     fun bitLength(value: BigInt): Int
     fun bitCount(value: BigInt): Int
     fun cmp(a: BigInt, b: BigInt): Int
+    fun gcd(a: BigInt, b: BigInt): BigInt
     fun pow(value: BigInt, n: Int): BigInt
     fun toByteArray(value: BigInt): ByteArray
     fun fromByteArray(bytes: ByteArray): BigInt

kbigint/src/jsTest/kotlin/io/github/observeroftime/kbigint/KBigIntTest.kt

@@ -75,6 +75,15 @@ actual class KBigIntTest {
         assertEquals(KBigInt(2147483649L), -long.inv())
     }
 
+    @Test
+    actual fun testGcdLcm() {
+        val a = KBigInt(-4)
+        val b = KBigInt(10)
+
+        assertEquals(KBigInt(2), a.gcd(b))
+        assertEquals(KBigInt(20), a.lcm(b))
+    }
+
     @Test
     actual fun testPow() {
         assertEquals(KBigInt("4611686018427387904"), long pow 2)

kbigint/src/jvmMain/kotlin/io/github/observeroftime/kbigint/KBigInt.kt

@@ -65,6 +65,14 @@ actual class KBigInt private constructor(private var value: BigInteger) : Compar
 
     actual infix fun xor(other: KBigInt) = KBigInt(value xor other.value)
 
+    actual fun gcd(other: KBigInt) = KBigInt(value.gcd(other.value))
+
+    actual fun lcm(other: KBigInt): KBigInt {
+        val a = value.abs()
+        val b = other.value.abs()
+        return KBigInt(a * b / a.gcd(b))
+    }
+
     @JvmName("shiftLeft")
     actual infix fun shl(n: Int) = KBigInt(value shl n)
 

kbigint/src/jvmTest/kotlin/io/github/observeroftime/kbigint/KBigIntTest.kt

@@ -75,6 +75,15 @@ actual class KBigIntTest {
         assertEquals(KBigInt(2147483649L), -long.inv())
     }
 
+    @Test
+    actual fun testGcdLcm() {
+        val a = KBigInt(-4)
+        val b = KBigInt(10)
+
+        assertEquals(KBigInt(2), a.gcd(b))
+        assertEquals(KBigInt(20), a.lcm(b))
+    }
+
     @Test
     actual fun testPow() {
         assertEquals(KBigInt("4611686018427387904"), long pow 2)