isPrintable function

bool isPrintable(int rune)

isPrintable reports whether the rune is defined as a Graphic by Unicode, except that the only spacing character is ASCII space, U+0020. Such characters include letters, marks, numbers, punctuation, and symbols from categories L, M, N, P, S.

Implementation

bool isPrintable(int rune) {
  // Fast check for Latin-1
  if (rune <= 0xFF) {
    if (0x20 <= rune && rune <= 0x7E) {
      // All the ASCII is printable from space through DEL-1.
      return true;
    }
    if (0xA1 <= rune && rune <= 0xFF) {
      // Similarly for ¡ through ÿ...
      return rune != 0xAD; // ...except for the bizarre soft hyphen.
    }
    return false;
  }

  // Same algorithm, either on uint16 or uint32 value.
  // First, find first i such that isPrint[i] >= x.
  // This is the index of either the start or end of a pair that might span x.
  // The start is even (isPrint[i&~1]) and the end is odd (isPrint[i|1]).
  // If we find x in a range, make sure x is not in isNotPrint list.

  int i, j;
  if (0 <= rune && rune < 1 << 16) {
    i = _bsearch(_isPrint16, rune);
    if (i >= _isPrint16.length ||
        rune < _isPrint16[i & ~1] ||
        _isPrint16[i | 1] < rune) {
      return false;
    }
    j = _bsearch(_isNotPrint16, rune);
    return j >= _isNotPrint16.length || _isNotPrint16[j] != rune;
  }

  i = _bsearch(_isPrint32, rune);
  if (i >= _isPrint32.length ||
      rune < _isPrint32[i & ~1] ||
      _isPrint32[i | 1] < rune) {
    return false;
  }
  if (rune >= 0x20000) {
    return true;
  }
  rune -= 0x10000;
  j = _bsearch(_isNotPrint32, rune);
  return j >= _isNotPrint32.length || _isNotPrint32[j] != rune;
}