implement numeric encodings, optimize

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

@@ -1,92 +1,15 @@
 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: UByteArray,
-    ): UByteArray
-
-    abstract fun decode(
-        bytes: UByteArray,
-    ): UByteArray
-
-    protected fun encode(
-        bytes: UByteArray,
-        characters: UByteArray,
-        padding: UByte? = null,
-    ): UByteArray {
-        val length = log2(characters.size).toInt()
-        val mask = (2.0.pow(length) - 1).toUInt()
-
-        val encoded = mutableListOf<UByte>()
-
-        var buffer = 0U
-        var bits = 0
-
-        for (byte in bytes) {
-            buffer = (buffer shl 8) + byte
-            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.toUByteArray()
+abstract class Encoding(
+    val alphabet: ByteArray,
+) {
+    init {
+        require(alphabet.isNotEmpty())
     }
 
-    protected fun decode(
-        bytes: UByteArray,
-        characters: UByteArray,
-        padding: UByte? = null,
-    ): UByteArray {
-        val length = log2(characters.size).toInt()
-        val mask = 0xffU
+    val base: Int
+        get() = alphabet.size
 
-        val decoded = mutableListOf<UByte>()
-
-        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).toUByte()
-                buffer = buffer and (mask shl offset).inv()
-                bits -= 8
-
-                decoded.add(character)
-            }
-        }
-
-        return decoded.toUByteArray()
-    }
+    abstract fun encode(bytes: ByteArray): ByteArray
+    abstract fun decode(bytes: ByteArray): ByteArray
 }