buf_add_txid(StringInfo buf, txid xid)
{
	TxidSnapshot *snap = (TxidSnapshot *) buf->data;

	/* do this before possible realloc */
	snap->nxip++;

	appendBinaryStringInfo(buf, (char *) &xid, sizeof(xid));
}

This weakness involves numeric computation errors, such as integer overflows, underflows, or precision losses, which can lead to miscalculations and exploitable behaviors in software.