XML_Parse(XML_Parser parser, const char *s, int len, int isFinal) {
  if ((parser == NULL) || (len < 0) || ((s == NULL) && (len != 0))) {
    if (parser != NULL)
      parser->m_errorCode = XML_ERROR_INVALID_ARGUMENT;
    return XML_STATUS_ERROR;
  }
  switch (parser->m_parsingStatus.parsing) {
  case XML_SUSPENDED:
    parser->m_errorCode = XML_ERROR_SUSPENDED;
    return XML_STATUS_ERROR;
  case XML_FINISHED:
    parser->m_errorCode = XML_ERROR_FINISHED;
    return XML_STATUS_ERROR;
  case XML_INITIALIZED:
    if (parser->m_parentParser == NULL && ! startParsing(parser)) {
      parser->m_errorCode = XML_ERROR_NO_MEMORY;
      return XML_STATUS_ERROR;
    }
    /* fall through */
  default:
    parser->m_parsingStatus.parsing = XML_PARSING;
  }

  if (len == 0) {
    parser->m_parsingStatus.finalBuffer = (XML_Bool)isFinal;
    if (! isFinal)
      return XML_STATUS_OK;
    parser->m_positionPtr = parser->m_bufferPtr;
    parser->m_parseEndPtr = parser->m_bufferEnd;

    /* If data are left over from last buffer, and we now know that these
       data are the final chunk of input, then we have to check them again
       to detect errors based on that fact.
    */
    parser->m_errorCode
        = parser->m_processor(parser, parser->m_bufferPtr,
                              parser->m_parseEndPtr, &parser->m_bufferPtr);

    if (parser->m_errorCode == XML_ERROR_NONE) {
      switch (parser->m_parsingStatus.parsing) {
      case XML_SUSPENDED:
        /* It is hard to be certain, but it seems that this case
         * cannot occur.  This code is cleaning up a previous parse
         * with no new data (since len == 0).  Changing the parsing
         * state requires getting to execute a handler function, and
         * there doesn't seem to be an opportunity for that while in
         * this circumstance.
         *
         * Given the uncertainty, we retain the code but exclude it
         * from coverage tests.
         *
         * LCOV_EXCL_START
         */
        XmlUpdatePosition(parser->m_encoding, parser->m_positionPtr,
                          parser->m_bufferPtr, &parser->m_position);
        parser->m_positionPtr = parser->m_bufferPtr;
        return XML_STATUS_SUSPENDED;
        /* LCOV_EXCL_STOP */
      case XML_INITIALIZED:
      case XML_PARSING:
        parser->m_parsingStatus.parsing = XML_FINISHED;
        /* fall through */
      default:
        return XML_STATUS_OK;
      }
    }
    parser->m_eventEndPtr = parser->m_eventPtr;
    parser->m_processor = errorProcessor;
    return XML_STATUS_ERROR;
  }
#ifndef XML_CONTEXT_BYTES
  else if (parser->m_bufferPtr == parser->m_bufferEnd) {
    const char *end;
    int nLeftOver;
    enum XML_Status result;
    /* Detect overflow (a+b > MAX <==> b > MAX-a) */
    if (len > ((XML_Size)-1) / 2 - parser->m_parseEndByteIndex) {
      parser->m_errorCode = XML_ERROR_NO_MEMORY;
      parser->m_eventPtr = parser->m_eventEndPtr = NULL;
      parser->m_processor = errorProcessor;
      return XML_STATUS_ERROR;
    }
    parser->m_parseEndByteIndex += len;
    parser->m_positionPtr = s;
    parser->m_parsingStatus.finalBuffer = (XML_Bool)isFinal;

    parser->m_errorCode
        = parser->m_processor(parser, s, parser->m_parseEndPtr = s + len, &end);

    if (parser->m_errorCode != XML_ERROR_NONE) {
      parser->m_eventEndPtr = parser->m_eventPtr;
      parser->m_processor = errorProcessor;
      return XML_STATUS_ERROR;
    } else {
      switch (parser->m_parsingStatus.parsing) {
      case XML_SUSPENDED:
        result = XML_STATUS_SUSPENDED;
        break;
      case XML_INITIALIZED:
      case XML_PARSING:
        if (isFinal) {
          parser->m_parsingStatus.parsing = XML_FINISHED;
          return XML_STATUS_OK;
        }
      /* fall through */
      default:
        result = XML_STATUS_OK;
      }
    }

    XmlUpdatePosition(parser->m_encoding, parser->m_positionPtr, end,
                      &parser->m_position);
    nLeftOver = s + len - end;
    if (nLeftOver) {
      if (parser->m_buffer == NULL
          || nLeftOver > parser->m_bufferLim - parser->m_buffer) {
        /* avoid _signed_ integer overflow */
        char *temp = NULL;
        const int bytesToAllocate = (int)((unsigned)len * 2U);
        if (bytesToAllocate > 0) {
          temp = (char *)REALLOC(parser, parser->m_buffer, bytesToAllocate);
        }
        if (temp == NULL) {
          parser->m_errorCode = XML_ERROR_NO_MEMORY;
          parser->m_eventPtr = parser->m_eventEndPtr = NULL;
          parser->m_processor = errorProcessor;
          return XML_STATUS_ERROR;
        }
        parser->m_buffer = temp;
        parser->m_bufferLim = parser->m_buffer + bytesToAllocate;
      }
      memcpy(parser->m_buffer, end, nLeftOver);
    }
    parser->m_bufferPtr = parser->m_buffer;
    parser->m_bufferEnd = parser->m_buffer + nLeftOver;
    parser->m_positionPtr = parser->m_bufferPtr;
    parser->m_parseEndPtr = parser->m_bufferEnd;
    parser->m_eventPtr = parser->m_bufferPtr;
    parser->m_eventEndPtr = parser->m_bufferPtr;
    return result;
  }
#endif /* not defined XML_CONTEXT_BYTES */
  else {
    void *buff = XML_GetBuffer(parser, len);
    if (buff == NULL)
      return XML_STATUS_ERROR;
    else {
      memcpy(buff, s, len);
      return XML_ParseBuffer(parser, len, isFinal);
    }
  }
}