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annotate libtommath/bn_mp_to_radix.c @ 1917:f8ed10efaaac

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author Matt Johnston <matt@ucc.asn.au>
date Wed, 30 Mar 2022 11:51:56 +0800
parents 1051e4eea25a
children
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1692
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_TO_RADIX_C
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
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4 /* SPDX-License-Identifier: Unlicense */
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5
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6 /* stores a bignum as a ASCII string in a given radix (2..64)
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7 *
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8 * Stores upto "size - 1" chars and always a NULL byte, puts the number of characters
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9 * written, including the '\0', in "written".
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10 */
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11 mp_err mp_to_radix(const mp_int *a, char *str, size_t maxlen, size_t *written, int radix)
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12 {
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13 size_t digs;
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14 mp_err err;
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15 mp_int t;
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16 mp_digit d;
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17 char *_s = str;
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18
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19 /* check range of radix and size*/
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20 if (maxlen < 2u) {
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21 return MP_BUF;
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22 }
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23 if ((radix < 2) || (radix > 64)) {
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24 return MP_VAL;
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25 }
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26
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27 /* quick out if its zero */
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28 if (MP_IS_ZERO(a)) {
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29 *str++ = '0';
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30 *str = '\0';
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31 if (written != NULL) {
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32 *written = 2u;
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33 }
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34 return MP_OKAY;
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35 }
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36
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37 if ((err = mp_init_copy(&t, a)) != MP_OKAY) {
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38 return err;
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39 }
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40
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41 /* if it is negative output a - */
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42 if (t.sign == MP_NEG) {
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43 /* we have to reverse our digits later... but not the - sign!! */
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44 ++_s;
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45
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46 /* store the flag and mark the number as positive */
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47 *str++ = '-';
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48 t.sign = MP_ZPOS;
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49
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50 /* subtract a char */
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51 --maxlen;
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52 }
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53 digs = 0u;
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54 while (!MP_IS_ZERO(&t)) {
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55 if (--maxlen < 1u) {
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56 /* no more room */
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57 err = MP_BUF;
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58 goto LBL_ERR;
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59 }
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60 if ((err = mp_div_d(&t, (mp_digit)radix, &t, &d)) != MP_OKAY) {
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61 goto LBL_ERR;
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62 }
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63 *str++ = mp_s_rmap[d];
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64 ++digs;
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65 }
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66 /* reverse the digits of the string. In this case _s points
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67 * to the first digit [exluding the sign] of the number
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68 */
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69 s_mp_reverse((unsigned char *)_s, digs);
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70
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71 /* append a NULL so the string is properly terminated */
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72 *str = '\0';
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73 digs++;
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74
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75 if (written != NULL) {
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76 *written = (a->sign == MP_NEG) ? (digs + 1u): digs;
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77 }
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78
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79 LBL_ERR:
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80 mp_clear(&t);
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81 return err;
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82 }
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83
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84 #endif