lib/oid_registry.c

/* ASN.1 Object identifier (OID) registry
 *
 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

#include <linux/export.h>
#include <linux/oid_registry.h>
#include "oid_registry_data.c"

/**
 * look_up_OID - Find an OID registration for the specified data
 * @data: Binary representation of the OID
 * @datasize: Size of the binary representation
 */
enum OID look_up_OID(const void *data, size_t datasize)
{
	const unsigned char *octets = data;
	enum OID oid;
	unsigned char xhash;
	unsigned i, j, k, hash;
	size_t len;

	/* Hash the OID data */
	hash = datasize - 1;

	for (i = 0; i < datasize; i++)
		hash += octets[i] * 33;
	hash = (hash >> 24) ^ (hash >> 16) ^ (hash >> 8) ^ hash;
	hash &= 0xff;

	/* Binary search the OID registry.  OIDs are stored in ascending order
	 * of hash value then ascending order of size and then in ascending
	 * order of reverse value.
	 */
	i = 0;
	k = OID__NR;
	while (i < k) {
		j = (i + k) / 2;

		xhash = oid_search_table[j].hash;
		if (xhash > hash) {
			k = j;
			continue;
		}
		if (xhash < hash) {
			i = j + 1;
			continue;
		}

		oid = oid_search_table[j].oid;
		len = oid_index[oid + 1] - oid_index[oid];
		if (len > datasize) {
			k = j;
			continue;
		}
		if (len < datasize) {
			i = j + 1;
			continue;
		}

		/* Variation is most likely to be at the tail end of the
		 * OID, so do the comparison in reverse.
		 */
		while (len > 0) {
			unsigned char a = oid_data[oid_index[oid] + --len];
			unsigned char b = octets[len];
			if (a > b) {
				k = j;
				goto next;
			}
			if (a < b) {
				i = j + 1;
				goto next;
			}
		}
		return oid;
	next:
		;
	}

	return OID__NR;
}
EXPORT_SYMBOL_GPL(look_up_OID);