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json4s-scalap
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/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2007-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */
package org.json4s.scalap

object ByteCodecs {

  def regenerateZero(src: Array[Byte]): Int = {
    var i = 0
    val srclen = src.length
    var j = 0
    while (i < srclen) {
      val in: Int = src(i) & 0xff
      if (in == 0xc0 && (src(i + 1) & 0xff) == 0x80) {
        src(j) = 0x7f
        i += 2
      } else if (in == 0) {
        src(j) = 0x7f
        i += 1
      } else {
        src(j) = (in - 1).toByte
        i += 1
      }
      j += 1
    }
    j
  }

  def decode7to8(src: Array[Byte], srclen: Int): Int = {
    var i = 0
    var j = 0
    val dstlen = (srclen * 7 + 7) / 8
    while (i + 7 < srclen) {
      var out: Int = src(i).toInt
      var in: Byte = src(i + 1)
      src(j) = (out | (in & 0x01) << 7).toByte
      out = in >>> 1
      in = src(i + 2)
      src(j + 1) = (out | (in & 0x03) << 6).toByte
      out = in >>> 2
      in = src(i + 3)
      src(j + 2) = (out | (in & 0x07) << 5).toByte
      out = in >>> 3
      in = src(i + 4)
      src(j + 3) = (out | (in & 0x0f) << 4).toByte
      out = in >>> 4
      in = src(i + 5)
      src(j + 4) = (out | (in & 0x1f) << 3).toByte
      out = in >>> 5
      in = src(i + 6)
      src(j + 5) = (out | (in & 0x3f) << 2).toByte
      out = in >>> 6
      in = src(i + 7)
      src(j + 6) = (out | in << 1).toByte
      i += 8
      j += 7
    }
    if (i < srclen) {
      var out: Int = src(i).toInt
      if (i + 1 < srclen) {
        var in: Byte = src(i + 1)
        src(j) = (out | (in & 0x01) << 7).toByte; j += 1
        out = in >>> 1
        if (i + 2 < srclen) {
          in = src(i + 2)
          src(j) = (out | (in & 0x03) << 6).toByte; j += 1
          out = in >>> 2
          if (i + 3 < srclen) {
            in = src(i + 3)
            src(j) = (out | (in & 0x07) << 5).toByte; j += 1
            out = in >>> 3
            if (i + 4 < srclen) {
              in = src(i + 4)
              src(j) = (out | (in & 0x0f) << 4).toByte; j += 1
              out = in >>> 4
              if (i + 5 < srclen) {
                in = src(i + 5)
                src(j) = (out | (in & 0x1f) << 3).toByte; j += 1
                out = in >>> 5
                if (i + 6 < srclen) {
                  in = src(i + 6)
                  src(j) = (out | (in & 0x3f) << 2).toByte; j += 1
                  out = in >>> 6
                }
              }
            }
          }
        }
      }
      if (j < dstlen) src(j) = out.toByte
    }
    dstlen
  }

  def decode(xs: Array[Byte]): Int = {
    val len = regenerateZero(xs)
    decode7to8(xs, len)
  }
}