CRC5.scala

import java.nio.charset.Charset

import org.scalatest.{Matchers, WordSpec}

import scala.util.Random

class CRC5Spec extends WordSpec with Matchers {

  /**
    * Implements a "normal" MSB-first byte-width CRC5 function using a lookup table.
    * See the <a href="http://reveng.sourceforge.net/crc-catalogue/">Catalogue of
    * parametrised CRC algorithms</a> for more information on these algorithms and
    * others.
    */
  object CRC5 {

    /* Params for CRC-5/EPC */
    val bitWidth = 5
    val poly = 0x09
    val initial = 0x09
    val xorOut = 0

    val table: Seq[Int] = {
      val widthMask = (1 << bitWidth) - 1
      val shpoly = poly << (8 - bitWidth)
      for (i <- 0 until 256) yield {
        var crc = i
        for (_ <- 0 until 8) {
          crc = if ((crc & 0x80) != 0) (crc << 1) ^ shpoly else crc << 1
        }
        (crc >> (8 - bitWidth)) & widthMask
      }
    }

    val ASCII = Charset.forName("ASCII")

    def calculate(string: String): Int = calculate(string.getBytes())

    def calculate(input: Array[Byte]): Int = {
      val start = 0
      val length = input.length
      var crc = initial ^ xorOut
      for (i <- 0 until length) {
        crc = table((crc << (8 - bitWidth)) ^ (input(start + i) & 0xff)) & 0xff
      }
      crc ^ xorOut
    }
  }

  "CRC5" should {
    "calculate checksum" in {
      CRC5.calculate("AB") shouldBe CRC5.calculate("AB")
      CRC5.calculate("AB") should not be CRC5.calculate("BA")
      CRC5.calculate("ABC") should not be CRC5.calculate("ACB")
      CRC5.calculate("ABC") should not be CRC5.calculate("BAC")
      CRC5.calculate("ABC") should not be CRC5.calculate("CBA")
      CRC5.calculate("ABCDEFGHIJKLMNOPRSTUWXYZ0123456789") shouldBe CRC5.calculate("ABCDEFGHIJKLMNOPRSTUWXYZ0123456789")
      CRC5.calculate("ABCDEFGHIJKLMNOPRSTUWXYZ0123456789") should not be CRC5.calculate("ABCDEFGHIJKLMNPORSTUWXYZ0123456789")
      CRC5.calculate("ABCDEFGHIJKLMNOPRSTUWXYZ0123456789") should not be CRC5.calculate("ABCDEFGHIJKLMNOORSTUWXYZ0123456789")
      CRC5.calculate("ABCDEFGHIJKLMNOPRSTUWXYZ0123456789") should not be CRC5.calculate("aBCDEFGHIJKLMNOPRSTUWXYZ0123456789")
    }
  }
}