mp_to_radix.c

   1 #include "tommath_private.h"
   2 #ifdef MP_TO_RADIX_C
   3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
   4 /* SPDX-License-Identifier: Unlicense */
   5
   6 /* reverse an array, used for radix code */
   7 static void s_reverse(char *s, size_t len)
   8 {
   9    size_t ix = 0, iy = len - 1u;
  10    while (ix < iy) {
  11       MP_EXCH(char, s[ix], s[iy]);
  12       ++ix;
  13       --iy;
  14    }
  15 }
  16
  17 /* stores a bignum as a ASCII string in a given radix (2..64)
  18  *
  19  * Stores upto "size - 1" chars and always a NULL byte, puts the number of characters
  20  * written, including the '\0', in "written".
  21  */
  22 mp_err mp_to_radix(const mp_int *a, char *str, size_t maxlen, size_t *written, int radix)
  23 {
  24    size_t  digs;
  25    mp_err  err;
  26    mp_int  t;
  27    mp_digit d;
  28    char   *_s = str;
  29
  30    /* check range of radix and size*/
  31    if (maxlen < 2u) {
  32       return MP_BUF;
  33    }
  34    if ((radix < 2) || (radix > 64)) {
  35       return MP_VAL;
  36    }
  37
  38    /* quick out if its zero */
  39    if (mp_iszero(a)) {
  40       *str++ = '0';
  41       *str = '\0';
  42       if (written != NULL) {
  43          *written = 2u;
  44       }
  45       return MP_OKAY;
  46    }
  47
  48    if ((err = mp_init_copy(&t, a)) != MP_OKAY) {
  49       return err;
  50    }
  51
  52    /* if it is negative output a - */
  53    if (mp_isneg(&t)) {
  54       /* we have to reverse our digits later... but not the - sign!! */
  55       ++_s;
  56
  57       /* store the flag and mark the number as positive */
  58       *str++ = '-';
  59       t.sign = MP_ZPOS;
  60
  61       /* subtract a char */
  62       --maxlen;
  63    }
  64    digs = 0u;
  65    while (!mp_iszero(&t)) {
  66       if (--maxlen < 1u) {
  67          /* no more room */
  68          err = MP_BUF;
  69          goto LBL_ERR;
  70       }
  71       if ((err = mp_div_d(&t, (mp_digit)radix, &t, &d)) != MP_OKAY) {
  72          goto LBL_ERR;
  73       }
  74       *str++ = s_mp_radix_map[d];
  75       ++digs;
  76    }
  77    /* reverse the digits of the string.  In this case _s points
  78     * to the first digit [excluding the sign] of the number
  79     */
  80    s_reverse(_s, digs);
  81
  82    /* append a NULL so the string is properly terminated */
  83    *str = '\0';
  84    digs++;
  85
  86    if (written != NULL) {
  87       *written = mp_isneg(a) ? (digs + 1u): digs;
  88    }
  89
  90 LBL_ERR:
  91    mp_clear(&t);
  92    return err;
  93 }
  94
  95 #endif