annotate bn_mp_mul_d.c @ 139:cc04b085e7dd libtommath

Pristine compilation works.
author Matt Johnston <matt@ucc.asn.au>
date Fri, 17 Dec 2004 06:27:22 +0000
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children d29b64170cf0
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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 /* multiply by a digit */
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18 int
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19 mp_mul_d (mp_int * a, mp_digit b, mp_int * c)
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20 {
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21 mp_digit u, *tmpa, *tmpc;
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22 mp_word r;
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23 int ix, res, olduse;
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24
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25 /* make sure c is big enough to hold a*b */
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26 if (c->alloc < a->used + 1) {
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27 if ((res = mp_grow (c, a->used + 1)) != MP_OKAY) {
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28 return res;
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29 }
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30 }
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31
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32 /* get the original destinations used count */
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33 olduse = c->used;
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34
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35 /* set the sign */
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36 c->sign = a->sign;
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37
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38 /* alias for a->dp [source] */
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39 tmpa = a->dp;
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40
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41 /* alias for c->dp [dest] */
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42 tmpc = c->dp;
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43
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44 /* zero carry */
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45 u = 0;
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46
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47 /* compute columns */
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48 for (ix = 0; ix < a->used; ix++) {
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49 /* compute product and carry sum for this term */
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50 r = ((mp_word) u) + ((mp_word)*tmpa++) * ((mp_word)b);
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51
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52 /* mask off higher bits to get a single digit */
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53 *tmpc++ = (mp_digit) (r & ((mp_word) MP_MASK));
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54
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55 /* send carry into next iteration */
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56 u = (mp_digit) (r >> ((mp_word) DIGIT_BIT));
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57 }
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58
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59 /* store final carry [if any] */
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60 *tmpc++ = u;
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61
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62 /* now zero digits above the top */
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63 while (ix++ < olduse) {
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64 *tmpc++ = 0;
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65 }
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66
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67 /* set used count */
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68 c->used = a->used + 1;
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69 mp_clamp(c);
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70
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71 return MP_OKAY;
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72 }