annotate bn_mp_radix_size.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 /* returns size of ASCII reprensentation */
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18 int mp_radix_size (mp_int * a, int radix, int *size)
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19 {
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20 int res, digs;
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21 mp_int t;
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22 mp_digit d;
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23
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24 *size = 0;
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25
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26 /* special case for binary */
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27 if (radix == 2) {
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28 *size = mp_count_bits (a) + (a->sign == MP_NEG ? 1 : 0) + 1;
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29 return MP_OKAY;
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30 }
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31
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32 /* make sure the radix is in range */
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33 if (radix < 2 || radix > 64) {
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34 return MP_VAL;
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35 }
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36
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37 /* init a copy of the input */
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38 if ((res = mp_init_copy (&t, a)) != MP_OKAY) {
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39 return res;
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40 }
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41
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42 /* digs is the digit count */
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43 digs = 0;
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44
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45 /* if it's negative add one for the sign */
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46 if (t.sign == MP_NEG) {
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47 ++digs;
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48 t.sign = MP_ZPOS;
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49 }
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50
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51 /* fetch out all of the digits */
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52 while (mp_iszero (&t) == 0) {
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53 if ((res = mp_div_d (&t, (mp_digit) radix, &t, &d)) != MP_OKAY) {
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54 mp_clear (&t);
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55 return res;
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56 }
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57 ++digs;
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58 }
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59 mp_clear (&t);
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60
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61 /* return digs + 1, the 1 is for the NULL byte that would be required. */
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62 *size = digs + 1;
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63 return MP_OKAY;
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64 }
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65