Mercurial > dropbear

annotate libtommath/bn_mp_mul_2d.c @ 476:df7f7da7f6e4 pubkey-options

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- Rework pubkey options to be more careful about buffer lengths. Needs review.
author Matt Johnston <matt@ucc.asn.au>
date Fri, 12 Sep 2008 17:23:56 +0000
parents 5ff8218bcee9
children 60fc6476e044
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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diff changeset
1 #include <tommath.h>
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2 #ifdef BN_MP_MUL_2D_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 /* shift left by a certain bit count */
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19 int mp_mul_2d (mp_int * a, int b, mp_int * c)
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20 {
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21 mp_digit d;
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22 int res;
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23
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24 /* copy */
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25 if (a != c) {
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26 if ((res = mp_copy (a, c)) != MP_OKAY) {
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27 return res;
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28 }
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29 }
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30
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31 if (c->alloc < (int)(c->used + b/DIGIT_BIT + 1)) {
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32 if ((res = mp_grow (c, c->used + b / DIGIT_BIT + 1)) != MP_OKAY) {
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33 return res;
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34 }
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35 }
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36
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37 /* shift by as many digits in the bit count */
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38 if (b >= (int)DIGIT_BIT) {
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39 if ((res = mp_lshd (c, b / DIGIT_BIT)) != MP_OKAY) {
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40 return res;
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41 }
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42 }
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43
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44 /* shift any bit count < DIGIT_BIT */
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45 d = (mp_digit) (b % DIGIT_BIT);
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46 if (d != 0) {
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47 register mp_digit *tmpc, shift, mask, r, rr;
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48 register int x;
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49
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50 /* bitmask for carries */
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51 mask = (((mp_digit)1) << d) - 1;
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52
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53 /* shift for msbs */
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54 shift = DIGIT_BIT - d;
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55
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56 /* alias */
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57 tmpc = c->dp;
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58
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59 /* carry */
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60 r = 0;
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61 for (x = 0; x < c->used; x++) {
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62 /* get the higher bits of the current word */
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63 rr = (*tmpc >> shift) & mask;
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64
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65 /* shift the current word and OR in the carry */
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66 *tmpc = ((*tmpc << d) | r) & MP_MASK;
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67 ++tmpc;
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68
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69 /* set the carry to the carry bits of the current word */
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70 r = rr;
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71 }
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72
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73 /* set final carry */
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74 if (r != 0) {
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75 c->dp[(c->used)++] = r;
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76 }
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77 }
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78 mp_clamp (c);
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79 return MP_OKAY;
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80 }
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81 #endif
389
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82
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83 /* $Source: /cvs/libtom/libtommath/bn_mp_mul_2d.c,v $ */
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84 /* $Revision: 1.3 $ */
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85 /* $Date: 2006/03/31 14:18:44 $ */