annotate bn_mp_toradix_n.c @ 1:22d5cf7d4b1a libtommath

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author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:23:46 +0000
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1 /* LibTomMath, multiple-precision integer library -- Tom St Denis
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2 *
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3 * LibTomMath is a library that provides multiple-precision
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4 * integer arithmetic as well as number theoretic functionality.
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5 *
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6 * The library was designed directly after the MPI library by
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7 * Michael Fromberger but has been written from scratch with
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8 * additional optimizations in place.
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9 *
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10 * The library is free for all purposes without any express
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11 * guarantee it works.
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12 *
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13 * Tom St Denis, [email protected], http://math.libtomcrypt.org
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14 */
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15 #include <tommath.h>
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16
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17 /* stores a bignum as a ASCII string in a given radix (2..64)
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18 *
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19 * Stores upto maxlen-1 chars and always a NULL byte
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20 */
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21 int mp_toradix_n(mp_int * a, char *str, int radix, int maxlen)
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22 {
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23 int res, digs;
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24 mp_int t;
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25 mp_digit d;
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26 char *_s = str;
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27
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28 /* check range of the maxlen, radix */
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29 if (maxlen < 3 || radix < 2 || radix > 64) {
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30 return MP_VAL;
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31 }
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32
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33 /* quick out if its zero */
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34 if (mp_iszero(a) == 1) {
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35 *str++ = '0';
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36 *str = '\0';
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37 return MP_OKAY;
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38 }
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39
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40 if ((res = mp_init_copy (&t, a)) != MP_OKAY) {
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41 return res;
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42 }
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43
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44 /* if it is negative output a - */
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45 if (t.sign == MP_NEG) {
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46 /* we have to reverse our digits later... but not the - sign!! */
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47 ++_s;
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48
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49 /* store the flag and mark the number as positive */
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50 *str++ = '-';
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51 t.sign = MP_ZPOS;
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52
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53 /* subtract a char */
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54 --maxlen;
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55 }
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56
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57 digs = 0;
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58 while (mp_iszero (&t) == 0) {
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59 if ((res = mp_div_d (&t, (mp_digit) radix, &t, &d)) != MP_OKAY) {
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60 mp_clear (&t);
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61 return res;
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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 if (--maxlen == 1) {
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67 /* no more room */
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68 break;
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69 }
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70 }
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71
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72 /* reverse the digits of the string. In this case _s points
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73 * to the first digit [exluding the sign] of the number]
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74 */
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75 bn_reverse ((unsigned char *)_s, digs);
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76
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77 /* append a NULL so the string is properly terminated */
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78 *str = '\0';
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79
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80 mp_clear (&t);
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81 return MP_OKAY;
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82 }
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83