1 /* Title: Pure/System/utf8.scala |
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2 Author: Makarius |
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3 |
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4 Variations on UTF-8. |
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5 */ |
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6 |
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7 package isabelle |
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8 |
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9 |
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10 import java.nio.charset.Charset |
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11 import scala.io.Codec |
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12 |
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13 |
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14 object UTF8 |
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15 { |
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16 /* charset */ |
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17 |
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18 val charset_name: String = "UTF-8" |
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19 val charset: Charset = Charset.forName(charset_name) |
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20 def codec(): Codec = Codec(charset) |
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21 |
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22 def bytes(s: String): Array[Byte] = s.getBytes(charset) |
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23 |
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24 object Length extends Codepoint.Length |
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25 { |
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26 override def codepoint_length(c: Int): Int = |
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27 if (c < 0x80) 1 |
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28 else if (c < 0x800) 2 |
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29 else if (c < 0x10000) 3 |
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30 else 4 |
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31 } |
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32 |
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33 |
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34 /* permissive UTF-8 decoding */ |
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35 |
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36 // see also http://en.wikipedia.org/wiki/UTF-8#Description |
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37 // overlong encodings enable byte-stuffing of low-ASCII |
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38 |
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39 def decode_permissive(text: CharSequence): String = |
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40 { |
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41 val buf = new java.lang.StringBuilder(text.length) |
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42 var code = -1 |
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43 var rest = 0 |
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44 def flush() |
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45 { |
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46 if (code != -1) { |
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47 if (rest == 0 && Character.isValidCodePoint(code)) |
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48 buf.appendCodePoint(code) |
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49 else buf.append('\uFFFD') |
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50 code = -1 |
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51 rest = 0 |
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52 } |
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53 } |
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54 def init(x: Int, n: Int) |
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55 { |
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56 flush() |
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57 code = x |
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58 rest = n |
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59 } |
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60 def push(x: Int) |
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61 { |
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62 if (rest <= 0) init(x, -1) |
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63 else { |
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64 code <<= 6 |
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65 code += x |
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66 rest -= 1 |
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67 } |
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68 } |
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69 for (i <- 0 until text.length) { |
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70 val c = text.charAt(i) |
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71 if (c < 128) { flush(); buf.append(c) } |
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72 else if ((c & 0xC0) == 0x80) push(c & 0x3F) |
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73 else if ((c & 0xE0) == 0xC0) init(c & 0x1F, 1) |
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74 else if ((c & 0xF0) == 0xE0) init(c & 0x0F, 2) |
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75 else if ((c & 0xF8) == 0xF0) init(c & 0x07, 3) |
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76 } |
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77 flush() |
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78 buf.toString |
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79 } |
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80 |
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81 private class Decode_Chars(decode: String => String, |
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82 buffer: Array[Byte], start: Int, end: Int) extends CharSequence |
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83 { |
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84 def length: Int = end - start |
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85 def charAt(i: Int): Char = (buffer(start + i).asInstanceOf[Int] & 0xFF).asInstanceOf[Char] |
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86 def subSequence(i: Int, j: Int): CharSequence = |
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87 new Decode_Chars(decode, buffer, start + i, start + j) |
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88 |
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89 // toString with adhoc decoding: abuse of CharSequence interface |
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90 override def toString: String = decode(decode_permissive(this)) |
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91 } |
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92 |
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93 def decode_chars(decode: String => String, |
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94 buffer: Array[Byte], start: Int, end: Int): CharSequence = |
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95 { |
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96 require(0 <= start && start <= end && end <= buffer.length) |
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97 new Decode_Chars(decode, buffer, start, end) |
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98 } |
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99 } |
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