周易 BASE 六十四卦

Hexagram64.kt

import java.io.ByteArrayOutputStream

object Hexagram64 {
    private const val zero = '䷀'
    private const val nil = '⚋'

    fun parse(string: String): ByteArray = ByteArrayOutputStream(128).use { stream ->
        var count = 0
        var length = 0
        var data = 0

        for (char in string) {
            val bits = if (char == nil) -1 else char.minus(zero).takeIf { it in 0..64 } ?: continue

            data = data shl 6 or bits.coerceAtLeast(0)
            if(bits > -1) length++

            if (++count > 3) {
                count = 0
                while (length-- > 1) {
                    stream.write(data and 0xFF0000 ushr 16)
                    data = data shl 8 and 0xFFFFFF
                }
            }
        }

        stream.toByteArray()
    }

    fun rend(byteArray: ByteArray): String = StringBuilder().apply {
        val size = byteArray.size

        var padding = 0
        var i = 0
        while (i < size) {
            var group = 0

            repeat(3) {
                group = group shl 8
                if (i < size) group = group or (byteArray[i++].toInt() and 0xFF) else padding++
            }

            repeat(4 - padding) {
                val index = group ushr 18 and 0x3F
                append(zero + index)
                group = group shl 6
            }
        }

        repeat(padding) { append(nil) }

    }.toString()
}

fun main() {
    val content = "Hello world!"
    val encoded = Hexagram64.rend(content.toByteArray())
    val decoded = String(Hexagram64.parse(encoded), Charsets.UTF_8)

    println("""
        Origin  : $content
        Encoded : $encoded
        Decoded : $decoded
    """.trimIndent())
}