81 lines
2.3 KiB
Kotlin
81 lines
2.3 KiB
Kotlin
package com.infendro.encoding
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import com.infendro.encoding.exception.IllegalByteException
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import com.infendro.encoding.util.align
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import com.infendro.encoding.util.divCeil
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import com.infendro.encoding.util.lcm
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import com.infendro.encoding.util.log2
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class StreamEncoding internal constructor(
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private val alphabet: ByteArray,
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private val padding: Byte? = null,
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) : Encoding {
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private val base: Int = alphabet.size
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private val bits: Int = log2(base).toInt()
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private val block: Int = lcm(bits, 8) / bits
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private val mask: Int = (0x01 shl bits) - 1
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override fun encode(bytes: ByteArray): ByteArray {
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val size = when (padding) {
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null -> (bytes.size * 8).divCeil(bits)
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else -> (bytes.size * 8).divCeil(bits).align(block)
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}
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val encoded = ByteArray(size)
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var i = 0
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var buffer = 0
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var bufferBits = 0
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for (byte in bytes) {
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buffer = (buffer shl 8) or (byte.toInt() and 0xFF)
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bufferBits += 8
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while (bufferBits >= bits) {
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val index = (buffer shr (bufferBits - bits)) and mask
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bufferBits -= bits
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encoded[i++] = alphabet[index]
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}
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}
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if (bufferBits > 0) {
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val index = (buffer shl (bits - bufferBits)) and mask
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encoded[i++] = alphabet[index]
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}
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while (i < encoded.size) {
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encoded[i++] = padding!!
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}
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return encoded
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}
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override fun decode(bytes: ByteArray): ByteArray {
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val end = when (padding) {
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null -> bytes.size
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else -> when (val index = bytes.indexOf(padding)) {
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-1 -> bytes.size
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else -> index
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}
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}
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val size = end * bits / 8
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val decoded = ByteArray(size)
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var i = 0
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var buffer = 0
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var bufferBits = 0
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for (b in 0..<end) {
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val byte = bytes[b]
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val index = alphabet.indexOf(byte)
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if (index == -1) throw IllegalByteException(byte)
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buffer = (buffer shl bits) or index
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bufferBits += bits
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if (bufferBits >= 8) {
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val byte = (buffer shr (bufferBits - 8)) and 0xFF
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bufferBits -= 8
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decoded[i++] = byte.toByte()
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}
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}
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return decoded
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}
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}
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