1 files changed, 81 insertions, 0 deletions
diff --git a/libtomcrypt/src/pk/asn1/der/integer/der_length_integer.c b/libtomcrypt/src/pk/asn1/der/integer/der_length_integer.c
new file mode 100644
index 0000000..1bfee45
--- /dev/null
+++ b/libtomcrypt/src/pk/asn1/der/integer/der_length_integer.c
@@ -0,0 +1,81 @@
+/* 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, tomstdenis@gmail.com, http://libtomcrypt.org
+ */
+#include "tomcrypt.h"
+
+/**
+  @file der_length_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 mp_int 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_integer(mp_int *num, unsigned long *outlen)
+{
+   unsigned long z, len;
+   int           leading_zero;
+
+   LTC_ARGCHK(num     != NULL);
+   LTC_ARGCHK(outlen  != NULL);
+
+   if (mp_cmp_d(num, 0) != MP_LT) {
+      /* positive */
+
+      /* we only need a leading zero if the msb of the first byte is one */
+      if ((mp_count_bits(num) & 7) == 0 || mp_iszero(num) == MP_YES) {
+         leading_zero = 1;
+      } else {
+         leading_zero = 0;
+      }
+
+      /* size for bignum */
+      z = len = leading_zero + mp_unsigned_bin_size(num);
+   } else {
+      /* it's negative */
+      /* find power of 2 that is a multiple of eight and greater than count bits */
+      leading_zero = 0;
+      z = mp_count_bits(num);
+      z = z + (8 - (z & 7));
+      len = z = z >> 3;
+   }
+
+   /* now we need a length */
+   if (z < 128) {
+      /* short form */
+      ++len;
+   } else {
+      /* long form (relies on z != 0), assumes length bytes < 128 */
+      ++len;
+
+      while (z) {
+         ++len;
+         z >>= 8;
+      }
+   }
+
+   /* we need a 0x02 to indicate it's INTEGER */
+   ++len;
+
+   /* return length */
+   *outlen = len; 
+   return CRYPT_OK;
+}
+
+#endif
+
+/* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/integer/der_length_integer.c,v $ */
+/* $Revision: 1.1 $ */
+/* $Date: 2005/05/16 15:08:11 $ */