lib/hcrypto/libtommath/bn_mp_to_radix.c

   1 #include "tommath_private.h"
   2 #ifdef BN_MP_TO_RADIX_C
   3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
   4 /* SPDX-License-Identifier: Unlicense */
   5
   6 /* stores a bignum as a ASCII string in a given radix (2..64)
   7  *
   8  * Stores upto "size - 1" chars and always a NULL byte, puts the number of characters
   9  * written, including the '\0', in "written".
  10  */
  11 mp_err mp_to_radix(const mp_int *a, char *str, size_t maxlen, size_t *written, int radix)
  12 {
  13    size_t  digs;
  14    mp_err  err;
  15    mp_int  t;
  16    mp_digit d;
  17    char   *_s = str;
  18
  19    /* check range of radix and size*/
  20    if (maxlen < 2u) {
  21       return MP_BUF;
  22    }
  23    if ((radix < 2) || (radix > 64)) {
  24       return MP_VAL;
  25    }
  26
  27    /* quick out if its zero */
  28    if (MP_IS_ZERO(a)) {
  29       *str++ = '0';
  30       *str = '\0';
  31       if (written != NULL) {
  32          *written = 2u;
  33       }
  34       return MP_OKAY;
  35    }
  36
  37    if ((err = mp_init_copy(&t, a)) != MP_OKAY) {
  38       return err;
  39    }
  40
  41    /* if it is negative output a - */
  42    if (t.sign == MP_NEG) {
  43       /* we have to reverse our digits later... but not the - sign!! */
  44       ++_s;
  45
  46       /* store the flag and mark the number as positive */
  47       *str++ = '-';
  48       t.sign = MP_ZPOS;
  49
  50       /* subtract a char */
  51       --maxlen;
  52    }
  53    digs = 0u;
  54    while (!MP_IS_ZERO(&t)) {
  55       if (--maxlen < 1u) {
  56          /* no more room */
  57          err = MP_BUF;
  58          goto LBL_ERR;
  59       }
  60       if ((err = mp_div_d(&t, (mp_digit)radix, &t, &d)) != MP_OKAY) {
  61          goto LBL_ERR;
  62       }
  63       *str++ = mp_s_rmap[d];
  64       ++digs;
  65    }
  66    /* reverse the digits of the string.  In this case _s points
  67     * to the first digit [exluding the sign] of the number
  68     */
  69    s_mp_reverse((unsigned char *)_s, digs);
  70
  71    /* append a NULL so the string is properly terminated */
  72    *str = '\0';
  73    digs++;
  74
  75    if (written != NULL) {
  76       *written = (a->sign == MP_NEG) ? (digs + 1u): digs;
  77    }
  78
  79 LBL_ERR:
  80    mp_clear(&t);
  81    return err;
  82 }
  83
  84 #endif