Mercurial > dropbear

annotate libtommath/bn_mp_mul_d.c @ 779:095b46180bbc

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Added tag DROPBEAR_2013.57 for changeset 96b8bcb88017
author Matt Johnston <matt@ucc.asn.au>
date Mon, 15 Apr 2013 22:10:49 +0800
parents 5ff8218bcee9
children 60fc6476e044
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1 #include <tommath.h>
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2 #ifdef BN_MP_MUL_D_C
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
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4 *
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5 * LibTomMath is a library that provides multiple-precision
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6 * integer arithmetic as well as number theoretic functionality.
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7 *
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8 * The library was designed directly after the MPI library by
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9 * Michael Fromberger but has been written from scratch with
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10 * additional optimizations in place.
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11 *
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12 * The library is free for all purposes without any express
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13 * guarantee it works.
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14 *
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15 * Tom St Denis, [email protected], http://math.libtomcrypt.com
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16 */
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17
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18 /* multiply by a digit */
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19 int
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20 mp_mul_d (mp_int * a, mp_digit b, mp_int * c)
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21 {
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22 mp_digit u, *tmpa, *tmpc;
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23 mp_word r;
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24 int ix, res, olduse;
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25
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26 /* make sure c is big enough to hold a*b */
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27 if (c->alloc < a->used + 1) {
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28 if ((res = mp_grow (c, a->used + 1)) != MP_OKAY) {
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29 return res;
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30 }
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31 }
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32
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33 /* get the original destinations used count */
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34 olduse = c->used;
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35
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36 /* set the sign */
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37 c->sign = a->sign;
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38
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39 /* alias for a->dp [source] */
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40 tmpa = a->dp;
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41
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42 /* alias for c->dp [dest] */
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43 tmpc = c->dp;
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44
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45 /* zero carry */
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46 u = 0;
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47
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48 /* compute columns */
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49 for (ix = 0; ix < a->used; ix++) {
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50 /* compute product and carry sum for this term */
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51 r = ((mp_word) u) + ((mp_word)*tmpa++) * ((mp_word)b);
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52
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53 /* mask off higher bits to get a single digit */
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54 *tmpc++ = (mp_digit) (r & ((mp_word) MP_MASK));
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55
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56 /* send carry into next iteration */
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57 u = (mp_digit) (r >> ((mp_word) DIGIT_BIT));
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58 }
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59
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60 /* store final carry [if any] and increment ix offset */
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61 *tmpc++ = u;
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62 ++ix;
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63
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64 /* now zero digits above the top */
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65 while (ix++ < olduse) {
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66 *tmpc++ = 0;
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67 }
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68
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69 /* set used count */
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70 c->used = a->used + 1;
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71 mp_clamp(c);
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72
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73 return MP_OKAY;
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74 }
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75 #endif
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76
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77 /* $Source: /cvs/libtom/libtommath/bn_mp_mul_d.c,v $ */
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78 /* $Revision: 1.3 $ */
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79 /* $Date: 2006/03/31 14:18:44 $ */