initial commit

src/commonMain/kotlin/com/infendro/encoding/Base32.kt

@@ -0,0 +1,31 @@
+package com.infendro.encoding
+
+object Base32 : Encoding() {
+    private val CHARACTERS = arrayOf<Byte>(
+        0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48,
+        0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50,
+        0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58,
+        0x59, 0x5a, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
+    )
+    private const val PADDING: Byte = 0x3d
+
+    override fun encode(
+        bytes: ByteArray,
+    ): ByteArray {
+        return encode(
+            bytes,
+            CHARACTERS,
+            PADDING,
+        )
+    }
+
+    override fun decode(
+        bytes: ByteArray,
+    ): ByteArray {
+        return decode(
+            bytes,
+            CHARACTERS,
+            PADDING,
+        )
+    }
+}

src/commonMain/kotlin/com/infendro/encoding/Base64.kt

@@ -0,0 +1,35 @@
+package com.infendro.encoding
+
+object Base64 : Encoding() {
+    private val CHARACTERS = arrayOf<Byte>(
+        0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48,
+        0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50,
+        0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58,
+        0x59, 0x5a, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66,
+        0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e,
+        0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76,
+        0x77, 0x78, 0x79, 0x7a, 0x30, 0x31, 0x32, 0x33,
+        0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x2b, 0x2f,
+    )
+    private const val PADDING: Byte = 0x3d
+
+    override fun encode(
+        bytes: ByteArray,
+    ): ByteArray {
+        return encode(
+            bytes,
+            CHARACTERS,
+            PADDING,
+        )
+    }
+
+    override fun decode(
+        bytes: ByteArray,
+    ): ByteArray {
+        return decode(
+            bytes,
+            CHARACTERS,
+            PADDING,
+        )
+    }
+}

src/commonMain/kotlin/com/infendro/encoding/Binary.kt

@@ -0,0 +1,25 @@
+package com.infendro.encoding
+
+object Binary : Encoding() {
+    private val CHARACTERS = arrayOf<Byte>(
+        0x30, 0x31,
+    )
+
+    override fun encode(
+        bytes: ByteArray,
+    ): ByteArray {
+        return encode(
+            bytes,
+            CHARACTERS,
+        )
+    }
+
+    override fun decode(
+        bytes: ByteArray,
+    ): ByteArray {
+        return decode(
+            bytes,
+            CHARACTERS,
+        )
+    }
+}

src/commonMain/kotlin/com/infendro/encoding/Encoding.kt

@@ -0,0 +1,92 @@
+package com.infendro.encoding
+
+import com.infendro.encoding.util.lcm
+import com.infendro.encoding.util.log2
+import kotlin.math.pow
+
+sealed class Encoding {
+    abstract fun encode(
+        bytes: ByteArray,
+    ): ByteArray
+
+    abstract fun decode(
+        bytes: ByteArray,
+    ): ByteArray
+
+    protected fun encode(
+        bytes: ByteArray,
+        characters: Array<Byte>,
+        padding: Byte? = null,
+    ): ByteArray {
+        val length = log2(characters.size).toInt()
+        val mask = (2.0.pow(length) - 1).toUInt()
+
+        val encoded = mutableListOf<Byte>()
+
+        var buffer = 0U
+        var bits = 0
+
+        for (byte in bytes) {
+            buffer = (buffer shl 8) + byte.toUByte()
+            bits += 8
+
+            while (bits >= length) {
+                val offset = bits - length
+                val index = (buffer shr offset).toInt()
+                buffer = buffer and (mask shl offset).inv()
+                bits -= length
+
+                encoded.add(characters[index])
+            }
+        }
+        if (bits > 0) {
+            buffer = buffer shl (length - bits)
+            val index = buffer.toInt()
+            encoded.add(characters[index])
+        }
+
+        if (padding != null) {
+            val block = lcm(length, 8) / length
+            while (encoded.size % block != 0) {
+                encoded.add(padding)
+            }
+        }
+
+        return encoded.toByteArray()
+    }
+
+    protected fun decode(
+        bytes: ByteArray,
+        characters: Array<Byte>,
+        padding: Byte? = null,
+    ): ByteArray {
+        val length = log2(characters.size).toInt()
+        val mask = 0xFFU
+
+        val decoded = mutableListOf<Byte>()
+
+        var buffer = 0U
+        var bits = 0
+
+        for (byte in bytes) {
+            if (byte == padding) break
+
+            val index = characters.indexOf(byte)
+            if (index == -1) throw Exception()
+
+            buffer = (buffer shl length) + index.toUByte()
+            bits += length
+
+            if (bits >= 8) {
+                val offset = bits - 8
+                val character = (buffer shr offset).toByte()
+                buffer = buffer and (mask shl offset).inv()
+                bits -= 8
+
+                decoded.add(character)
+            }
+        }
+
+        return decoded.toByteArray()
+    }
+}

src/commonMain/kotlin/com/infendro/encoding/Hex.kt

@@ -0,0 +1,26 @@
+package com.infendro.encoding
+
+object Hex : Encoding() {
+    private val CHARACTERS = arrayOf<Byte>(
+        0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
+        0x38, 0x39, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66,
+    )
+
+    override fun encode(
+        bytes: ByteArray,
+    ): ByteArray {
+        return encode(
+            bytes,
+            CHARACTERS,
+        )
+    }
+
+    override fun decode(
+        bytes: ByteArray,
+    ): ByteArray {
+        return decode(
+            bytes,
+            CHARACTERS,
+        )
+    }
+}

src/commonMain/kotlin/com/infendro/encoding/Main.kt

@@ -0,0 +1,11 @@
+package com.infendro.encoding
+
+fun main() {
+    val value = "ABC"
+    val a0 = Binary.encode(value.encodeToByteArray())
+    val a1 = Binary.decode(a0)
+
+    println(value)
+    println(a0.decodeToString())
+    println(a1.decodeToString())
+}

src/commonMain/kotlin/com/infendro/encoding/util/Math.kt

@@ -0,0 +1,31 @@
+package com.infendro.encoding.util
+
+import kotlin.math.log2
+
+internal fun log2(
+    value: Int,
+): Double {
+    val x = value.toDouble()
+    return log2(x)
+}
+
+internal fun gcd(
+    a: Int,
+    b: Int,
+): Int {
+    var x = a
+    var y = b
+    while (y != 0) {
+        val temp = y
+        y = x % y
+        x = temp
+    }
+    return x
+}
+
+internal fun lcm(
+    a: Int,
+    b: Int,
+): Int {
+    return (a * b) / gcd(a, b)
+}