74 lines
2.2 KiB
Kotlin
74 lines
2.2 KiB
Kotlin
package com.infendro.encoding.util
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internal class BigInt private constructor(
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val words: IntArray,
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) {
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init {
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require(words.isNotEmpty())
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}
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fun isZero(): Boolean = words.all { it == 0 }
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fun timesAdd(multiplier: Int, addend: Int): BigInt {
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val product = IntArray(words.size)
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var carry = addend
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for (i in words.indices) {
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val current = (words[i].toLong() and 0xFFFFFFFFL) * multiplier + carry
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product[i] = current.toInt()
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carry = (current ushr 32).toInt()
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}
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when {
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carry > 0 -> {
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val expanded = product.copyOf(product.size + 1)
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expanded[product.size] = carry
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return BigInt(expanded)
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}
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else -> return BigInt(product)
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}
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}
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fun divRem(divisor: Int): Pair<BigInt, Int> {
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val quotient = IntArray(words.size)
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var remainder = 0
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for (i in words.indices.reversed()) {
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val current = (remainder.toLong() shl 32) or (words[i].toLong() and 0xFFFFFFFFL)
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quotient[i] = (current / divisor.toLong()).toInt()
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remainder = (current % divisor.toLong()).toInt()
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}
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when {
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quotient.size > 1 && quotient.last() == 0 -> {
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val contracted = quotient.copyOfRange(0, quotient.size - 1)
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return Pair(BigInt(contracted), remainder)
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}
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else -> return Pair(BigInt(quotient), remainder)
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}
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}
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fun toByteArray(): ByteArray {
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val bytes = ByteArray((words.size * 4) - words.last().countLeadingZeroBytes())
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for (i in bytes.indices) {
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val (wi, bi) = (bytes.lastIndex - i).divRem(4)
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bytes[i] = (words[wi] ushr (bi * 8)).toByte()
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}
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return bytes
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}
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companion object {
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val zero: BigInt
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get() = BigInt(intArrayOf(0))
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fun from(bytes: ByteArray): BigInt {
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val words = IntArray(bytes.size.ceilDiv(4))
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for (i in bytes.indices) {
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val (wi, bi) = (bytes.lastIndex - i).divRem(4)
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words[wi] = words[wi] or ((bytes[i].toInt() and 0xFF) shl (bi * 8))
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}
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return BigInt(words)
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}
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}
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}
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