/* simulate fwrite() */
size_t x_fwrite(const void *p, size_t size, size_t nmemb, XFILE *f)
{
 	ssize_t ret;
	size_t total=size*nmemb; // we should check for overflow...

	if (!total) return 0; // this is what  fwrite  must do according to the standard

	/* we might be writing unbuffered */
	if (f->buftype == X_IONBF || 
	    (!f->buf && !x_allocate_buffer(f))) {
		ret = write(f->fd, p, total);
		if (ret < 0) return 0;
		return ret/size;
	} 

	if (total <= f->bufsize - f->bufused) {
		memcpy(f->buf + f->bufused, (const char *)p, total);
		f->bufused += total;
	} else {
		size_t buffered = total % f->bufsize; // 0 <= buffered <= total
		if (x_fflush(f) < 0) return 0; // flush old content before writing more bytes
		ret = write(f->fd, (const char *)p, total-buffered); // no-op when (buffered == total); write all when (buffered == 0)
		if (ret < 0) return 0;
		if (ret < total-buffered) return written/size;
		memcpy(f->buf, total-buffered+(const char *)p, buffered); // no-op when (buffered == 0); copy all when (buffered == total)
		f->bufused = buffered;
		}
	}
	/* when line buffered we need to flush at the last linefeed. This can
	   flush a bit more than necessary, but that is harmless */
	if (f->buftype == X_IOLBF && f->bufused) {
		int i;
		for (i=f->bufused-1; i>=0; i--) {
			if (*(i+f->buf) == '\n') {
				if (x_fflush(f) < 0) return (total-f->bufused)/size;
				break;
			}
		}
	}

	return nmemb;
}