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

@@ -3,4 +3,4 @@ package com.infendro.encoding
 private val alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567".encodeToByteArray()
 private const val padding = '='.code.toByte()
 
-object Base32 : Encoding by StreamEncoding(alphabet, padding)
+object Base32 : Encoding by PaddedStreamEncoding(alphabet, padding)

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

@@ -3,4 +3,4 @@ package com.infendro.encoding
 private val alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".encodeToByteArray()
 private const val padding = '='.code.toByte()
 
-object Base64 : Encoding by StreamEncoding(alphabet, padding)
+object Base64 : Encoding by PaddedStreamEncoding(alphabet, padding)

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

@@ -2,8 +2,6 @@ package com.infendro.encoding
 
 import com.infendro.encoding.exception.IllegalByteException
 import com.infendro.encoding.util.BigInt
-import com.infendro.encoding.util.log2
-import kotlin.math.ceil
 
 class NumericEncoding internal constructor(
     override val alphabet: ByteArray,
@@ -11,18 +9,16 @@ class NumericEncoding internal constructor(
     override fun encode(bytes: ByteArray): ByteArray {
         if (bytes.isEmpty()) return byteArrayOf()
 
-        val size = ceil(bytes.size * 8 / log2(base)).toInt()
-        val result = ByteArray(size)
+        val result = mutableListOf<Byte>()
 
-        var i = result.size
         var x = BigInt.from(bytes)
         while (!x.isZero()) {
             val (quotient, remainder) = x.divRem(base)
             x = quotient
-            result[--i] = alphabet[remainder]
+            result += alphabet[remainder]
         }
 
-        return result.copyOfRange(i, result.size)
+        return result.asReversed().toByteArray()
     }
 
     override fun decode(bytes: ByteArray): ByteArray {

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

@@ -0,0 +1,78 @@
+package com.infendro.encoding
+
+import com.infendro.encoding.exception.IllegalByteException
+import com.infendro.encoding.util.align
+import com.infendro.encoding.util.divCeil
+import com.infendro.encoding.util.lcm
+import com.infendro.encoding.util.log2
+
+class PaddedStreamEncoding internal constructor(
+    override val alphabet: ByteArray,
+    private val padding: Byte,
+) : Encoding {
+    override fun encode(bytes: ByteArray): ByteArray {
+        val bits = log2(base).toInt()
+
+        val block = lcm(bits, 8) / bits
+        val size = (bytes.size * 8).divCeil(bits).align(block)
+        val result = ByteArray(size)
+
+        var r = 0
+        var buffer = 0
+        var bufferBits = 0
+        for (i in bytes.indices) {
+            buffer = (buffer shl 8) + bytes[i]
+            bufferBits += 8
+
+            while (bufferBits >= bits) {
+                val offset = bufferBits - bits
+                val index = (buffer ushr offset)
+                buffer = buffer and ((base - 1) shl offset).inv()
+                bufferBits -= bits
+
+                result[r++] = alphabet[index]
+            }
+        }
+        if (bufferBits > 0) {
+            val index = buffer shl (bits - bufferBits)
+            result[r++] = alphabet[index]
+        }
+        while (r < result.size) {
+            result[r++] = padding
+        }
+
+        return result
+    }
+
+    override fun decode(bytes: ByteArray): ByteArray {
+        val bits = log2(base).toInt()
+
+        val end = bytes.indexOf(padding).takeIf { it != -1 } ?: bytes.size
+        val size = end * bits / 8
+        val result = ByteArray(size)
+
+        var r = 0
+        var buffer = 0
+        var bufferBits = 0
+        for (i in 0..<end) {
+            val byte = bytes[i]
+
+            val value = alphabet.indexOf(byte)
+            if (value == -1) throw IllegalByteException(byte)
+
+            buffer = (buffer shl bits) + value.toByte()
+            bufferBits += bits
+
+            if (bufferBits >= 8) {
+                val offset = bufferBits - 8
+                val character = (buffer ushr offset).toByte()
+                buffer = buffer and (0xFF shl offset).inv()
+                bufferBits -= 8
+
+                result[r++] = character
+            }
+        }
+
+        return result
+    }
+}

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

@@ -1,30 +1,17 @@
 package com.infendro.encoding
 
 import com.infendro.encoding.exception.IllegalByteException
-import com.infendro.encoding.util.align
 import com.infendro.encoding.util.divCeil
-import com.infendro.encoding.util.lcm
 import com.infendro.encoding.util.log2
 
 class StreamEncoding internal constructor(
     override val alphabet: ByteArray,
-    private val padding: Byte? = null,
 ) : Encoding {
-    init {
-        require(base and (base - 1) == 0)
-    }
-
     override fun encode(bytes: ByteArray): ByteArray {
         val bits = log2(base).toInt()
+
         val size = (bytes.size * 8).divCeil(bits)
-        val encodedSize = when (padding) {
-            null -> size
-            else -> {
-                val block = lcm(bits, 8) / bits
-                size.align(block)
-            }
-        }
-        val result = ByteArray(encodedSize)
+        val result = ByteArray(size)
 
         var r = 0
         var buffer = 0
@@ -43,15 +30,8 @@ class StreamEncoding internal constructor(
             }
         }
         if (bufferBits > 0) {
-            buffer = buffer shl (bits - bufferBits)
-            val index = buffer
-            result[r++] = alphabet[index]
-        }
-
-        if (padding != null) {
-            while (r < result.size) {
-                result[r++] = padding
-            }
+            val index = buffer shl (bits - bufferBits)
+            result[r] = alphabet[index]
         }
 
         return result
@@ -59,24 +39,20 @@ class StreamEncoding internal constructor(
 
     override fun decode(bytes: ByteArray): ByteArray {
         val bits = log2(base).toInt()
-        val index = padding?.let { bytes.indexOf(it) } ?: -1
-        val decodedSize = when (index) {
-            -1 -> bytes.size * bits / 8
-            else -> index * bits / 8
-        }
-        val result = ByteArray(decodedSize)
+
+        val size = bytes.size * bits / 8
+        val result = ByteArray(size)
 
         var r = 0
         var buffer = 0
         var bufferBits = 0
         for (i in bytes.indices) {
             val byte = bytes[i]
-            if (byte == padding) break
 
-            val index = alphabet.indexOf(byte)
-            if (index == -1) throw IllegalByteException(byte)
+            val value = alphabet.indexOf(byte)
+            if (value == -1) throw IllegalByteException(byte)
 
-            buffer = (buffer shl bits) + index.toByte()
+            buffer = (buffer shl bits) + value.toByte()
             bufferBits += bits
 
             if (bufferBits >= 8) {