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/* Title: Pure/General/utf8.scala
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Author: Makarius
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Variations on UTF-8.
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*/
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package isabelle
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import java.nio.charset.Charset
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import scala.io.Codec
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object UTF8
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{
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/* charset */
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val charset_name: String = "UTF-8"
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val charset: Charset = Charset.forName(charset_name)
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def codec(): Codec = Codec(charset)
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def bytes(s: String): Array[Byte] = s.getBytes(charset)
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/* permissive UTF-8 decoding */
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// see also http://en.wikipedia.org/wiki/UTF-8#Description
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// overlong encodings enable byte-stuffing of low-ASCII
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def decode_permissive(text: CharSequence): String =
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{
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val buf = new java.lang.StringBuilder(text.length)
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var code = -1
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var rest = 0
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def flush()
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{
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if (code != -1) {
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if (rest == 0 && Character.isValidCodePoint(code))
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buf.appendCodePoint(code)
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else buf.append('\uFFFD')
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code = -1
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rest = 0
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}
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}
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def init(x: Int, n: Int)
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{
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flush()
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code = x
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rest = n
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}
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def push(x: Int)
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{
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if (rest <= 0) init(x, -1)
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else {
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code <<= 6
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code += x
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rest -= 1
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}
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}
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for (i <- 0 until text.length) {
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val c = text.charAt(i)
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if (c < 128) { flush(); buf.append(c) }
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else if ((c & 0xC0) == 0x80) push(c & 0x3F)
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else if ((c & 0xE0) == 0xC0) init(c & 0x1F, 1)
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else if ((c & 0xF0) == 0xE0) init(c & 0x0F, 2)
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else if ((c & 0xF8) == 0xF0) init(c & 0x07, 3)
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}
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flush()
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buf.toString
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}
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private class Decode_Chars(decode: String => String,
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buffer: Array[Byte], start: Int, end: Int) extends CharSequence
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{
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def length: Int = end - start
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def charAt(i: Int): Char = (buffer(start + i).asInstanceOf[Int] & 0xFF).asInstanceOf[Char]
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def subSequence(i: Int, j: Int): CharSequence =
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new Decode_Chars(decode, buffer, start + i, start + j)
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// toString with adhoc decoding: abuse of CharSequence interface
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override def toString: String = decode(decode_permissive(this))
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}
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def decode_chars(decode: String => String,
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buffer: Array[Byte], start: Int, end: Int): CharSequence =
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{
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require(0 <= start && start <= end && end <= buffer.length)
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new Decode_Chars(decode, buffer, start, end)
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}
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}
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