release/src/router/dropbear/libtommath/bn_mp_toradix_n.c

   1 #include <tommath.h>
   2 #ifdef BN_MP_TORADIX_N_C
   3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
   4  *
   5  * LibTomMath is a library that provides multiple-precision
   6  * integer arithmetic as well as number theoretic functionality.
   7  *
   8  * The library was designed directly after the MPI library by
   9  * Michael Fromberger but has been written from scratch with
  10  * additional optimizations in place.
  11  *
  12  * The library is free for all purposes without any express
  13  * guarantee it works.
  14  *
  15  * Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com
  16  */
  17
  18 /* stores a bignum as a ASCII string in a given radix (2..64)
  19  *
  20  * Stores upto maxlen-1 chars and always a NULL byte
  21  */
  22 int mp_toradix_n(mp_int * a, char *str, int radix, int maxlen)
  23 {
  24   int     res, digs;
  25   mp_int  t;
  26   mp_digit d;
  27   char   *_s = str;
  28
  29   /* check range of the maxlen, radix */
  30   if (maxlen < 2 || radix < 2 || radix > 64) {
  31     return MP_VAL;
  32   }
  33
  34   /* quick out if its zero */
  35   if (mp_iszero(a) == MP_YES) {
  36      *str++ = '0';
  37      *str = '\0';
  38      return MP_OKAY;
  39   }
  40
  41   if ((res = mp_init_copy (&t, a)) != MP_OKAY) {
  42     return res;
  43   }
  44
  45   /* if it is negative output a - */
  46   if (t.sign == MP_NEG) {
  47     /* we have to reverse our digits later... but not the - sign!! */
  48     ++_s;
  49
  50     /* store the flag and mark the number as positive */
  51     *str++ = '-';
  52     t.sign = MP_ZPOS;
  53
  54     /* subtract a char */
  55     --maxlen;
  56   }
  57
  58   digs = 0;
  59   while (mp_iszero (&t) == 0) {
  60     if (--maxlen < 1) {
  61        /* no more room */
  62        break;
  63     }
  64     if ((res = mp_div_d (&t, (mp_digit) radix, &t, &d)) != MP_OKAY) {
  65       mp_clear (&t);
  66       return res;
  67     }
  68     *str++ = mp_s_rmap[d];
  69     ++digs;
  70   }
  71
  72   /* reverse the digits of the string.  In this case _s points
  73    * to the first digit [exluding the sign] of the number
  74    */
  75   bn_reverse ((unsigned char *)_s, digs);
  76
  77   /* append a NULL so the string is properly terminated */
  78   *str = '\0';
  79
  80   mp_clear (&t);
  81   return MP_OKAY;
  82 }
  83
  84 #endif
  85
  86 /* $Source: /cvs/libtom/libtommath/bn_mp_toradix_n.c,v $ */
  87 /* $Revision: 1.4 $ */
  88 /* $Date: 2006/03/31 14:18:44 $ */