Infendro/encoding.kt
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split padding in StreamEncoding to PaddedStreamEncoding

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This commit is contained in:
Infendro
2026-01-20 09:52:58 +01:00
parent c1b8800e82
commit 8290955755
5 changed files with 93 additions and 43 deletions
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2
src/commonMain/kotlin/com/infendro/encoding/Base32.kt
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@@ -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)

2
src/commonMain/kotlin/com/infendro/encoding/Base64.kt
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@@ -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)

10
src/commonMain/kotlin/com/infendro/encoding/NumericEncoding.kt
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@@ -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 {

78
src/commonMain/kotlin/com/infendro/encoding/PaddedStreamEncoding.kt Normal file
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@@ -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
}
}

44
src/commonMain/kotlin/com/infendro/encoding/StreamEncoding.kt
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@@ -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) {