feat(core): implement bitLength & bitCount

Author: ObserverOfTime

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

@@ -13,13 +13,30 @@ actual class KBigInt private constructor(private var value: BigInteger) : Compar
 
     actual constructor(number: Long) : this(number.toBigInteger())
 
-    /** Convert a [ByteArray] to a [KBigInt]. */
     actual constructor(bytes: ByteArray) : this(BigInteger(bytes))
 
     @get:JvmName("signum")
     actual val sign: Int
         get() = value.signum()
 
+    /**
+     * The total number of bits in the value.
+     *
+     * @see [BigInteger.bitLength]
+     */
+    @get:JvmName("bitLength")
+    actual val bitLength: Int
+        get() = value.bitLength()
+
+    /**
+     * The number of set bits in the value.
+     *
+     * @see [BigInteger.bitCount]
+     */
+    @get:JvmName("bitCount")
+    actual val bitCount: Int
+        get() = value.bitCount()
+
     @JvmName("add")
     actual operator fun plus(other: KBigInt) = KBigInt(value + other.value)
 
@@ -113,6 +130,10 @@ actual class KBigInt private constructor(private var value: BigInteger) : Compar
      */
     fun toDouble() = value.toDouble()
 
-    /** Convert the value to a [ByteArray]. */
+    /**
+     * Convert the value to a [ByteArray].
+     *
+     * @see [BigInteger.toByteArray]
+     */
     actual fun toByteArray(): ByteArray = value.toByteArray()
 }

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

@@ -15,6 +15,26 @@ actual class KBigIntTest {
         assertEquals(-1, KBigInt(-2).sign)
     }
 
+    @Test
+    actual fun testBits() {
+        val a = KBigInt(1024)
+        val b = KBigInt(-1024)
+        val c = KBigInt(0)
+        val d = KBigInt(-1)
+
+        assertEquals(11, a.bitLength)
+        assertEquals(1, a.bitCount)
+
+        assertEquals(10, b.bitLength)
+        assertEquals(10, b.bitCount)
+
+        assertEquals(0, c.bitLength)
+        assertEquals(0, c.bitCount)
+
+        assertEquals(0, d.bitLength)
+        assertEquals(0, d.bitCount)
+    }
+
     @Test
     actual fun testArithmetic() {
         assertEquals(KBigInt("9223372039002259456"), string + long)

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

@@ -23,6 +23,12 @@ expect class KBigInt : Comparable<KBigInt> {
      */
     val sign: Int
 
+    /** The total number of bits in the value. */
+    val bitLength: Int
+
+    /** The number of set bits in the value. */
+    val bitCount: Int
+
     /** Add two [KBigInt] values. */
     operator fun plus(other: KBigInt): KBigInt
 

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

@@ -5,6 +5,7 @@ internal const val OVER_MAX_LONG = "9223372036854775808"
 
 expect class KBigIntTest {
     fun testSign()
+    fun testBits()
     fun testArithmetic()
     fun testIncDec()
     fun testNegate()

kbigint/src/javascript/kbigint-utils.mjs

@@ -10,6 +10,32 @@ export function sign(value) {
     return cmp(value, 0n);
 }
 
+/**
+ * Count the total number of bits in the value.
+ *
+ * @param value {bigint}
+ * @return {number}
+ * @see https://stackoverflow.com/a/76616288/21974435
+ */
+export function bitLength(value) {
+    const n = value >= 0n ? value : ~value;
+    const i = (n.toString(16).length - 1) >> 2;
+    return i + 32 - Math.clz32(Number(n >> BigInt(i)))
+}
+
+/**
+ * Count the number of set bits in the value.
+ *
+ * @param value {bigint}
+ * @return {number}
+ * @see https://stackoverflow.com/a/72518920/21974435
+ */
+export function bitCount(value) {
+    let n = (value >= 0n ? value : ~value), bits;
+    for (bits = 0; n > 0n; ++bits) n &= n - 1n;
+    return bits
+}
+
 /**
  * Return the absolute value.
  *

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

@@ -20,6 +20,12 @@ actual class KBigInt private constructor(@JsExternalArgument private var value:
     actual val sign: Int
         get() = KBigIntUtils.sign(value)
 
+    actual val bitLength: Int
+        get() = KBigIntUtils.bitLength(value)
+
+    actual val bitCount: Int
+        get() = KBigIntUtils.bitCount(value)
+
     @JsName("add")
     actual operator fun plus(other: KBigInt): KBigInt {
         val a = this.value

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

@@ -10,6 +10,8 @@ internal external object KBigIntUtils {
     fun sqrt(value: BigInt): BigInt
     fun abs(value: BigInt): BigInt
     fun sign(value: BigInt): Int
+    fun bitLength(value: BigInt): Int
+    fun bitCount(value: BigInt): Int
     fun cmp(a: BigInt, b: BigInt): Int
     fun pow(value: BigInt, n: Int): BigInt
     fun toByteArray(value: BigInt): ByteArray

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

@@ -15,6 +15,26 @@ actual class KBigIntTest {
         assertEquals(-1, KBigInt(-2).sign)
     }
 
+    @Test
+    actual fun testBits() {
+        val a = KBigInt(1024)
+        val b = KBigInt(-1024)
+        val c = KBigInt(0)
+        val d = KBigInt(-1)
+
+        assertEquals(11, a.bitLength)
+        assertEquals(1, a.bitCount)
+
+        assertEquals(10, b.bitLength)
+        assertEquals(10, b.bitCount)
+
+        assertEquals(0, c.bitLength)
+        assertEquals(0, c.bitCount)
+
+        assertEquals(0, d.bitLength)
+        assertEquals(0, d.bitCount)
+    }
+
     @Test
     actual fun testArithmetic() {
         assertEquals(KBigInt("9223372039002259456"), string + long)

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

@@ -11,13 +11,30 @@ actual class KBigInt private constructor(private var value: BigInteger) : Compar
 
     actual constructor(number: Long) : this(number.toBigInteger())
 
-    /** Convert a [ByteArray] to a [KBigInt]. */
     actual constructor(bytes: ByteArray) : this(BigInteger(bytes))
 
     @get:JvmName("signum")
     actual val sign: Int
         get() = value.signum()
 
+    /**
+     * The total number of bits in the value.
+     *
+     * @see [BigInteger.bitLength]
+     */
+    @get:JvmName("bitLength")
+    actual val bitLength: Int
+        get() = value.bitLength()
+
+    /**
+     * The number of set bits in the value.
+     *
+     * @see [BigInteger.bitCount]
+     */
+    @get:JvmName("bitCount")
+    actual val bitCount: Int
+        get() = value.bitCount()
+
     @JvmName("add")
     actual operator fun plus(other: KBigInt) = KBigInt(value + other.value)
 

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

@@ -15,6 +15,26 @@ actual class KBigIntTest {
         assertEquals(-1, KBigInt(-2).sign)
     }
 
+    @Test
+    actual fun testBits() {
+        val a = KBigInt(1024)
+        val b = KBigInt(-1024)
+        val c = KBigInt(0)
+        val d = KBigInt(-1)
+
+        assertEquals(11, a.bitLength)
+        assertEquals(1, a.bitCount)
+
+        assertEquals(10, b.bitLength)
+        assertEquals(10, b.bitCount)
+
+        assertEquals(0, c.bitLength)
+        assertEquals(0, c.bitCount)
+
+        assertEquals(0, d.bitLength)
+        assertEquals(0, d.bitCount)
+    }
+
     @Test
     actual fun testArithmetic() {
         assertEquals(KBigInt("9223372039002259456"), string + long)