src/Pure/library.scala

factored-out Library.decode_permissive_utf8;

/*  Title:      Pure/library.scala
    Author:     Makarius

Basic library.
*/

package isabelle

import java.lang.System


object Library
{
  /* reverse CharSequence */

  class Reverse(text: CharSequence, start: Int, end: Int) extends CharSequence
  {
    require(0 <= start && start <= end && end <= text.length)

    def this(text: CharSequence) = this(text, 0, text.length)

    def length: Int = end - start
    def charAt(i: Int): Char = text.charAt(end - i - 1)

    def subSequence(i: Int, j: Int): CharSequence =
      if (0 <= i && i <= j && j <= length) new Reverse(text, end - j, end - i)
      else throw new IndexOutOfBoundsException

    override def toString: String =
    {
      val buf = new StringBuilder(length)
      for (i <- 0 until length)
        buf.append(charAt(i))
      buf.toString
    }
  }


  /* permissive UTF-8 decoding */

  // see also http://en.wikipedia.org/wiki/UTF-8#Description
  def decode_permissive_utf8(text: CharSequence): String =
  {
    val buf = new java.lang.StringBuilder(text.length)
    var code = -1
    var rest = 0
    def flush()
    {
      if (code != -1) {
        if (rest == 0 && Character.isValidCodePoint(code))
          buf.appendCodePoint(code)
        else buf.append('\uFFFD')
        code = -1
        rest = 0
      }
    }
    def init(x: Int, n: Int)
    {
      flush()
      code = x
      rest = n
    }
    def push(x: Int)
    {
      if (rest <= 0) init(x, -1)
      else {
        code <<= 6
        code += x
        rest -= 1
      }
    }
    for (i <- 0 until text.length) {
      val c = text.charAt(i)
      if (c < 128) { flush(); buf.append(c) }
      else if ((c & 0xC0) == 0x80) push(c & 0x3F)
      else if ((c & 0xE0) == 0xC0) init(c & 0x1F, 1)
      else if ((c & 0xF0) == 0xE0) init(c & 0x0F, 2)
      else if ((c & 0xF8) == 0xF0) init(c & 0x07, 3)
    }
    flush()
    buf.toString
  }


  /* timing */

  def timeit[A](e: => A) =
  {
    val start = System.currentTimeMillis()
    val result = Exn.capture(e)
    val stop = System.currentTimeMillis()
    System.err.println((stop - start) + "ms elapsed time")
    Exn.release(result)
  }
}