isWideCodePoint function

Implementation

bool isWideCodePoint(int codePoint) {
  // Lowest wide character in Unicode is Hangul Jamo (0x1100).
  // Everything below 0x1100 (ASCII, Latin Extended, Cyrillic, Greek, Hebrew, Arabic) is 1 cell.
  if (codePoint < 0x1100) return false;

  // Ultra-fast paths for high-frequency CJK and Hangul text (99% of wide characters in real text)
  if (codePoint >= 0x4E00 && codePoint <= 0x9FFF) return true; // CJK Main
  if (codePoint >= 0xAC00 && codePoint <= 0xD7A3) {
    return true; // Hangul Syllables
  }
  if (codePoint >= 0x20000 && codePoint <= 0x2FFFD) {
    return true; // Plane 2 (Ext B..F, I)
  }
  if (codePoint >= 0x30000 && codePoint <= 0x3FFFD) {
    return true; // Plane 3 (Ext G..H)
  }

  // Binary search over remaining Unicode 16.0 wide intervals (max 7 iterations)
  int low = 0;
  int high = _wideRangeStarts.length - 1;
  while (low <= high) {
    final mid = (low + high) >> 1;
    if (codePoint < _wideRangeStarts[mid]) {
      high = mid - 1;
    } else if (codePoint > _wideRangeEnds[mid]) {
      low = mid + 1;
    } else {
      return true;
    }
  }

  return false;
}