src/commonMain/kotlin/com/infendro/encoding/Base45.kt

@@ -0,0 +1,51 @@
+package com.infendro.encoding
+
+import com.infendro.encoding.exception.IllegalByteException
+
+object Base45 : Encoding {
+    private val alphabet: ByteArray = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ $%*+-./:".encodeToByteArray()
+    private val base: Int = alphabet.size
+
+    override fun encode(bytes: ByteArray): ByteArray {
+        val result = mutableListOf<Byte>()
+
+        for (i in bytes.indices step 2) {
+            val remaining = minOf(bytes.size - i, 2)
+
+            var value = 0
+            for (j in 0..<remaining) {
+                val byte = bytes[i + j]
+                value = (value shl 8) or (byte.toInt() and 0xFF)
+            }
+
+            repeat(remaining + 1) {
+                result += alphabet[value % base]
+                value /= base
+            }
+        }
+
+        return result.toByteArray()
+    }
+
+    override fun decode(bytes: ByteArray): ByteArray {
+        val result = mutableListOf<Byte>()
+
+        for (i in bytes.indices step 3) {
+            val remaining = minOf(bytes.size - i, 3)
+
+            var value = 0
+            for (j in (0..<remaining).reversed()) {
+                val byte = bytes[i + j]
+                val index = alphabet.indexOf(byte)
+                if (index == -1) throw IllegalByteException(byte)
+                value = value * base + index
+            }
+
+            for (j in (0..<(remaining - 1)).reversed()) {
+                result += ((value shr (j * 8)) and 0xFF).toByte()
+            }
+        }
+
+        return result.toByteArray()
+    }
+}

src/commonTest/kotlin/com/infendro/encoding/Base45.kt

@@ -0,0 +1,36 @@
+package com.infendro.encoding
+
+import kotlin.test.Test
+import kotlin.test.assertContentEquals
+
+class `Base45 Test` {
+    val encoding: Encoding
+        get() = Base45
+
+    val original = "Hello World!".encodeToByteArray()
+    val encoded = "%69 VD82EI2B.KESTC".encodeToByteArray()
+
+    @Test
+    fun `encode empty`() {
+        val actual = encoding.encode(byteArrayOf())
+        assertContentEquals(byteArrayOf(), actual)
+    }
+
+    @Test
+    fun `decode empty`() {
+        val actual = encoding.decode(byteArrayOf())
+        assertContentEquals(byteArrayOf(), actual)
+    }
+
+    @Test
+    fun encode() {
+        val actual = encoding.encode(original)
+        assertContentEquals(encoded, actual)
+    }
+
+    @Test
+    fun decode() {
+        val actual = encoding.decode(encoded)
+        assertContentEquals(original, actual)
+    }
+}