All files / buffers/src/utf8/decodeUtf8 v7.ts

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export default (buf: Uint8Array, start: number, length: number): string => {
  let offset = start;
  const end = offset + length;
  const codes: Array<number> = [];
  while (offset < end) {
    const octet1 = buf[offset++]!;
    if ((octet1 & 0x80) === 0) {
      codes.push(octet1);
    } else if ((octet1 & 0xe0) === 0xc0) {
      const octet2 = buf[offset++]! & 0x3f;
      codes.push(((octet1 & 0x1f) << 6) | octet2);
    } else if ((octet1 & 0xf0) === 0xe0) {
      const octet2 = buf[offset++]! & 0x3f;
      const octet3 = buf[offset++]! & 0x3f;
      codes.push(((octet1 & 0x1f) << 12) | (octet2 << 6) | octet3);
    } else if ((octet1 & 0xf8) === 0xf0) {
      const octet2 = buf[offset++]! & 0x3f;
      const octet3 = buf[offset++]! & 0x3f;
      const octet4 = buf[offset++]! & 0x3f;
      let unit = ((octet1 & 0x07) << 0x12) | (octet2 << 0x0c) | (octet3 << 0x06) | octet4;
      if (unit > 0xffff) {
        unit -= 0x10000;
        codes.push(((unit >>> 10) & 0x3ff) | 0xd800);
        unit = 0xdc00 | (unit & 0x3ff);
      }
      codes.push(unit);
    } else E{
      codes.push(octet1);
    }
  }
  return String.fromCharCode(...codes);
};