libxml: parsing and writing XML in a snap

I've just finished to download libxml sources and documentation. Here's an excerpt that shows how libxml writes an XML document:

sum = 0;
    count = xmlOutputBufferWriteString(writer->out, "<?xml version=");
    if (count < 0)
        return -1;
    sum += count;
    count = xmlOutputBufferWrite(writer->out, 1, &writer->qchar);
    if (count < 0)
        return -1;
    sum += count;
    if (version != 0)
        count = xmlOutputBufferWriteString(writer->out, version);
    else
        count = xmlOutputBufferWriteString(writer->out, "1.0");
    if (count < 0)
        return -1;
    sum += count;
    count = xmlOutputBufferWrite(writer->out, 1, &writer->qchar);
    if (count < 0)
        return -1;
    sum += count;
    if (writer->out->encoder != 0) {
        count = xmlOutputBufferWriteString(writer->out, " encoding=");
        if (count < 0)
            return -1;
        sum += count;
        count = xmlOutputBufferWrite(writer->out, 1, &writer->qchar);
        if (count < 0)
            return -1;
        sum += count;
        count =
            xmlOutputBufferWriteString(writer->out,
                                       writer->out->encoder->name);
        if (count < 0)
            return -1;
        sum += count;
        count = xmlOutputBufferWrite(writer->out, 1, &writer->qchar);
        if (count < 0)
            return -1;
        sum += count;
    }

    if (standalone != 0) {
        count = xmlOutputBufferWriteString(writer->out, " standalone=");
        if (count < 0)
            return -1;
        sum += count;
        count = xmlOutputBufferWrite(writer->out, 1, &writer->qchar);
        if (count < 0)
            return -1;
        sum += count;
        count = xmlOutputBufferWriteString(writer->out, standalone);
        if (count < 0)
            return -1;
        sum += count;
        count = xmlOutputBufferWrite(writer->out, 1, &writer->qchar);
        if (count < 0)
            return -1;
        sum += count;
    }

    count = xmlOutputBufferWriteString(writer->out, "?>\n");
    if (count < 0)
        return -1;
    sum += count;

    return sum;

This is a buffered stream-based approach with strings. How fast is it? Believe me, it's faster than light!