1/* LibTomCrypt, modular cryptographic library -- Tom St Denis
2 *
3 * LibTomCrypt is a library that provides various cryptographic
4 * algorithms in a highly modular and flexible manner.
5 *
6 * The library is free for all purposes without any express
7 * guarantee it works.
8 *
9 * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com
10 */
11#include "tomcrypt.h"
12
13/**
14  @file der_length_short_integer.c
15  ASN.1 DER, get length of encoding, Tom St Denis
16*/
17
18
19#ifdef LTC_DER
20/**
21  Gets length of DER encoding of num
22  @param num    The integer to get the size of
23  @param outlen [out] The length of the DER encoding for the given integer
24  @return CRYPT_OK if successful
25*/
26int der_length_short_integer(unsigned long num, unsigned long *outlen)
27{
28   unsigned long z, y, len;
29
30   LTC_ARGCHK(outlen  != NULL);
31
32   /* force to 32 bits */
33   num &= 0xFFFFFFFFUL;
34
35   /* get the number of bytes */
36   z = 0;
37   y = num;
38   while (y) {
39     ++z;
40     y >>= 8;
41   }
42
43   /* handle zero */
44   if (z == 0) {
45      z = 1;
46   }
47
48   /* we need a 0x02 to indicate it's INTEGER */
49   len = 1;
50
51   /* length byte */
52   ++len;
53
54   /* bytes in value */
55   len += z;
56
57   /* see if msb is set */
58   len += (num&(1UL<<((z<<3) - 1))) ? 1 : 0;
59
60   /* return length */
61   *outlen = len;
62
63   return CRYPT_OK;
64}
65
66#endif
67
68/* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/short_integer/der_length_short_integer.c,v $ */
69/* $Revision: 1.5 $ */
70/* $Date: 2006/03/31 14:15:35 $ */
71