UnicodeString::doAppend(const UChar *srcChars, int32_t srcStart, int32_t srcLength) {
  if(!isWritable() || srcLength == 0 || srcChars == NULL) {
    return *this;
  }

  // Perform all remaining operations relative to srcChars + srcStart.
  // From this point forward, do not use srcStart.
  srcChars += srcStart;

  if(srcLength < 0) {
    // get the srcLength if necessary
    if((srcLength = u_strlen(srcChars)) == 0) {
      return *this;
    }
  }

  int32_t oldLength = length();
  int32_t newLength = oldLength + srcLength;

  // Check for append onto ourself
  const UChar* oldArray = getArrayStart();
  if (isBufferWritable() &&
      oldArray < srcChars + srcLength &&
      srcChars < oldArray + oldLength) {
    // Copy into a new UnicodeString and start over
    UnicodeString copy(srcChars, srcLength);
    if (copy.isBogus()) {
      setToBogus();
      return *this;
    }
    return doAppend(copy.getArrayStart(), 0, srcLength);
  }

  // optimize append() onto a large-enough, owned string
  if((newLength <= getCapacity() && isBufferWritable()) ||
      cloneArrayIfNeeded(newLength, getGrowCapacity(newLength))) {
    UChar *newArray = getArrayStart();
    // Do not copy characters when
    //   UChar *buffer=str.getAppendBuffer(...);
    // is followed by
    //   str.append(buffer, length);
    // or
    //   str.appendString(buffer, length)
    // or similar.
    if(srcChars != newArray + oldLength) {
      us_arrayCopy(srcChars, 0, newArray, oldLength, srcLength);
    }
    setLength(newLength);
  }
  return *this;
}
The software performs a calculation that can produce an integer overflow or wraparound, when the logic assumes that the resulting value will always be larger than the original value. This can introduce other weaknesses when the calculation is used for resource management or execution control.