All files / buffers/src/utf8/decodeUtf8 v1.ts

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export default (buf: Uint8Array, start: number, length: number): string => {
  let offset = start;
  const end = offset + length;
  const units: Array<number> = [];
  let result = '';
  while (offset < end) {
    const byte1 = buf[offset++]!;
    if ((byte1 & 0x80) === 0) {
      units.push(byte1);
    } else if ((byte1 & 0xe0) === 0xc0) {
      const byte2 = buf[offset++]! & 0x3f;
      units.push(((byte1 & 0x1f) << 6) | byte2);
    } else if ((byte1 & 0xf0) === 0xe0) {
      const byte2 = buf[offset++]! & 0x3f;
      const byte3 = buf[offset++]! & 0x3f;
      units.push(((byte1 & 0x1f) << 12) | (byte2 << 6) | byte3);
    } else if ((byte1 & 0xf8) === 0xf0) {
      const byte2 = buf[offset++]! & 0x3f;
      const byte3 = buf[offset++]! & 0x3f;
      const byte4 = buf[offset++]! & 0x3f;
      let unit = ((byte1 & 0x07) << 0x12) | (byte2 << 0x0c) | (byte3 << 0x06) | byte4;
      if (unit > 0xffff) {
        unit -= 0x10000;
        units.push(((unit >>> 10) & 0x3ff) | 0xd800);
        unit = 0xdc00 | (unit & 0x3ff);
      }
      units.push(unit);
    } else E{
      units.push(byte1);
    }
    if (units.length >= 1000) {
      result += String.fromCharCode(...units);
      units.length = 0;
    }
  }
  if (units.length > 0) result += String.fromCharCode(...units);
  return result;
};