Function UTF8ArrayToString

mkbitmap/mkbitmap.js:3350–3391

* Given a pointer 'idx' to a null-terminated UTF8-encoded string in the given * array that contains uint8 values, returns a copy of that string as a * Javascript String object. * heapOrArray is either a regular array, or a JavaScript typed array view. * @param {number} idx *

(heapOrArray, idx, maxBytesToRead)

     * @return {string}
     */
  function UTF8ArrayToString(heapOrArray, idx, maxBytesToRead) {
      var endIdx = idx + maxBytesToRead;
      var endPtr = idx;
      // TextDecoder needs to know the byte length in advance, it doesn't stop on
      // null terminator by itself.  Also, use the length info to avoid running tiny
      // strings through TextDecoder, since .subarray() allocates garbage.
      // (As a tiny code save trick, compare endPtr against endIdx using a negation,
      // so that undefined means Infinity)
      while (heapOrArray[endPtr] && !(endPtr >= endIdx)) ++endPtr;
  
      if (endPtr - idx > 16 && heapOrArray.buffer && UTF8Decoder) {
        return UTF8Decoder.decode(heapOrArray.subarray(idx, endPtr));
      }
      var str = '';
      // If building with TextDecoder, we have already computed the string length
      // above, so test loop end condition against that
      while (idx < endPtr) {
        // For UTF8 byte structure, see:
        // http://en.wikipedia.org/wiki/UTF-8#Description
        // https://www.ietf.org/rfc/rfc2279.txt
        // https://tools.ietf.org/html/rfc3629
        var u0 = heapOrArray[idx++];
        if (!(u0 & 0x80)) { str += String.fromCharCode(u0); continue; }
        var u1 = heapOrArray[idx++] & 63;
        if ((u0 & 0xE0) == 0xC0) { str += String.fromCharCode(((u0 & 31) << 6) | u1); continue; }
        var u2 = heapOrArray[idx++] & 63;
        if ((u0 & 0xF0) == 0xE0) {
          u0 = ((u0 & 15) << 12) | (u1 << 6) | u2;
        } else {
          if ((u0 & 0xF8) != 0xF0) warnOnce('Invalid UTF-8 leading byte ' + ptrToString(u0) + ' encountered when deserializing a UTF-8 string in wasm memory to a JS string!');
          u0 = ((u0 & 7) << 18) | (u1 << 12) | (u2 << 6) | (heapOrArray[idx++] & 63);
        }
  
        if (u0 < 0x10000) {
          str += String.fromCharCode(u0);
        } else {
          var ch = u0 - 0x10000;
          str += String.fromCharCode(0xD800 | (ch >> 10), 0xDC00 | (ch & 0x3FF));
        }
      }
      return str;
    }
  
  
    /**