diff src/pk/asn1/der/short_integer/der_length_short_integer.c @ 209:39d5d58461d6 libtomcrypt-orig LTC_1.05

Import of libtomcrypt 1.05
author Matt Johnston <matt@ucc.asn.au>
date Wed, 06 Jul 2005 03:53:40 +0000
parents
children d5faf4814ddb
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--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/pk/asn1/der/short_integer/der_length_short_integer.c	Wed Jul 06 03:53:40 2005 +0000
@@ -0,0 +1,69 @@
+/* LibTomCrypt, modular cryptographic library -- Tom St Denis
+ *
+ * LibTomCrypt is a library that provides various cryptographic
+ * algorithms in a highly modular and flexible manner.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ *
+ * Tom St Denis, [email protected], http://libtomcrypt.org
+ */
+#include "tomcrypt.h"
+
+/**
+  @file der_length_short_integer.c
+  ASN.1 DER, get length of encoding, Tom St Denis
+*/
+
+
+#ifdef LTC_DER
+/**
+  Gets length of DER encoding of num 
+  @param num    The integer to get the size of 
+  @param outlen [out] The length of the DER encoding for the given integer
+  @return CRYPT_OK if successful
+*/
+int der_length_short_integer(unsigned long num, unsigned long *outlen)
+{
+   unsigned long z, y, len;
+
+   LTC_ARGCHK(outlen  != NULL);
+
+   /* force to 32 bits */
+   num &= 0xFFFFFFFFUL;
+
+   /* get the number of bytes */
+   z = 0;
+   y = num;
+   while (y) {
+     ++z;
+     y >>= 8;
+   }
+
+   /* handle zero */
+   if (z == 0) {
+      z = 1;
+   }
+
+   /* we need a 0x02 to indicate it's INTEGER */
+   len = 1;
+
+   /* length byte */
+   ++len;
+
+   /* bytes in value */
+   len += z;
+
+   /* see if msb is set */
+   len += (num&(1UL<<((z<<3) - 1))) ? 1 : 0;
+
+   /* return length */
+   *outlen = len; 
+   return CRYPT_OK;
+}
+
+#endif
+
+/* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/short_integer/der_length_short_integer.c,v $ */
+/* $Revision: 1.3 $ */
+/* $Date: 2005/05/23 01:35:38 $ */