Function utf8Slice

stackgl_modules/index.js:834–896

(buf, start, end)

  }
}
function utf8Slice(buf, start, end) {
  end = Math.min(buf.length, end);
  var res = [];
  var i = start;
  while (i < end) {
    var firstByte = buf[i];
    var codePoint = null;
    var bytesPerSequence = firstByte > 0xEF ? 4 : firstByte > 0xDF ? 3 : firstByte > 0xBF ? 2 : 1;
    if (i + bytesPerSequence <= end) {
      var secondByte, thirdByte, fourthByte, tempCodePoint;
      switch (bytesPerSequence) {
        case 1:
          if (firstByte < 0x80) {
            codePoint = firstByte;
          }
          break;
        case 2:
          secondByte = buf[i + 1];
          if ((secondByte & 0xC0) === 0x80) {
            tempCodePoint = (firstByte & 0x1F) << 0x6 | secondByte & 0x3F;
            if (tempCodePoint > 0x7F) {
              codePoint = tempCodePoint;
            }
          }
          break;
        case 3:
          secondByte = buf[i + 1];
          thirdByte = buf[i + 2];
          if ((secondByte & 0xC0) === 0x80 && (thirdByte & 0xC0) === 0x80) {
            tempCodePoint = (firstByte & 0xF) << 0xC | (secondByte & 0x3F) << 0x6 | thirdByte & 0x3F;
            if (tempCodePoint > 0x7FF && (tempCodePoint < 0xD800 || tempCodePoint > 0xDFFF)) {
              codePoint = tempCodePoint;
            }
          }
          break;
        case 4:
          secondByte = buf[i + 1];
          thirdByte = buf[i + 2];
          fourthByte = buf[i + 3];
          if ((secondByte & 0xC0) === 0x80 && (thirdByte & 0xC0) === 0x80 && (fourthByte & 0xC0) === 0x80) {
            tempCodePoint = (firstByte & 0xF) << 0x12 | (secondByte & 0x3F) << 0xC | (thirdByte & 0x3F) << 0x6 | fourthByte & 0x3F;
            if (tempCodePoint > 0xFFFF && tempCodePoint < 0x110000) {
              codePoint = tempCodePoint;
            }
          }
      }
    }
    if (codePoint === null) {
      // we did not generate a valid codePoint so insert a
      // replacement char (U+FFFD) and advance only 1 byte
      codePoint = 0xFFFD;
      bytesPerSequence = 1;
    } else if (codePoint > 0xFFFF) {
      // encode to utf16 (surrogate pair dance)
      codePoint -= 0x10000;
      res.push(codePoint >>> 10 & 0x3FF | 0xD800);
      codePoint = 0xDC00 | codePoint & 0x3FF;
    }