text: /* 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://libtom.org
   */
  #include "tomcrypt.h"
  
  /**
    @file der_encode_short_integer.c
    ASN.1 DER, encode an integer, Tom St Denis
  */
  
  
  #ifdef LTC_DER
  
  /**
    Store a short integer in the range (0,2^32-1)
    @param num      The integer to encode
    @param out      [out] The destination for the DER encoded integers
    @param outlen   [in/out] The max size and resulting size of the DER encoded integers
    @return CRYPT_OK if successful
  */
  int der_encode_short_integer(unsigned long num, unsigned char *out, unsigned long *outlen)
  {  
     unsigned long len, x, y, z;
     int           err;
     
     LTC_ARGCHK(out    != NULL);
     LTC_ARGCHK(outlen != NULL);
  
     /* force to 32 bits */
     num &= 0xFFFFFFFFUL;
  
     /* find out how big this will be */
     if ((err = der_length_short_integer(num, &len)) != CRYPT_OK) {
        return err;
     }
  
     if (*outlen < len) {
        *outlen = len;
        return CRYPT_BUFFER_OVERFLOW;
     }
  
     /* get len of output */
     z = 0;
     y = num;
     while (y) {
       ++z;
       y >>= 8;
     }
  
     /* handle zero */
     if (z == 0) {
        z = 1;
     }
  
     /* see if msb is set */
     z += (num&(1UL<<((z<<3) - 1))) ? 1 : 0;
  
     /* adjust the number so the msB is non-zero */
     for (x = 0; (z <= 4) && (x < (4 - z)); x++) {
        num <<= 8;
     }
  
     /* store header */
     x = 0;
     out[x++] = 0x02;
     out[x++] = (unsigned char)z;
  
     /* if 31st bit is set output a leading zero and decrement count */
     if (z == 5) {
        out[x++] = 0;
        --z;
     }
  
     /* store values */
     for (y = 0; y < z; y++) {
        out[x++] = (unsigned char)((num >> 24) & 0xFF);
        num    <<= 8;
     }
  
     /* we good */
     *outlen = x;
   
     return CRYPT_OK;
  }
  
  #endif
  
  /* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/short_integer/der_encode_short_integer.c,v $ */
  /* $Revision: 1.8 $ */
  /* $Date: 2006/12/28 01:27:24 $ */
  