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annotate libtommath/bn_mp_add_d.c @ 1938:77bc00dcc19f default tip main master

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Bump version to 2022.82
author Matt Johnston <matt@ucc.asn.au>
date Fri, 01 Apr 2022 14:43:27 +0800
parents 1051e4eea25a
children
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_ADD_D_C
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
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4 /* SPDX-License-Identifier: Unlicense */
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6 /* single digit addition */
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7 mp_err mp_add_d(const mp_int *a, mp_digit b, mp_int *c)
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8 {
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9 mp_err err;
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10 int ix, oldused;
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11 mp_digit *tmpa, *tmpc;
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12
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13 /* grow c as required */
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14 if (c->alloc < (a->used + 1)) {
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15 if ((err = mp_grow(c, a->used + 1)) != MP_OKAY) {
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16 return err;
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17 }
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18 }
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19
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20 /* if a is negative and |a| >= b, call c = |a| - b */
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21 if ((a->sign == MP_NEG) && ((a->used > 1) || (a->dp[0] >= b))) {
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22 mp_int a_ = *a;
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23 /* temporarily fix sign of a */
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24 a_.sign = MP_ZPOS;
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26 /* c = |a| - b */
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27 err = mp_sub_d(&a_, b, c);
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28
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29 /* fix sign */
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30 c->sign = MP_NEG;
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31
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32 /* clamp */
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33 mp_clamp(c);
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34
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35 return err;
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36 }
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37
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38 /* old number of used digits in c */
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39 oldused = c->used;
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40
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41 /* source alias */
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42 tmpa = a->dp;
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43
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44 /* destination alias */
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45 tmpc = c->dp;
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47 /* if a is positive */
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48 if (a->sign == MP_ZPOS) {
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49 /* add digits, mu is carry */
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50 mp_digit mu = b;
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51 for (ix = 0; ix < a->used; ix++) {
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52 *tmpc = *tmpa++ + mu;
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53 mu = *tmpc >> MP_DIGIT_BIT;
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54 *tmpc++ &= MP_MASK;
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55 }
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56 /* set final carry */
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57 ix++;
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58 *tmpc++ = mu;
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59
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60 /* setup size */
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61 c->used = a->used + 1;
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62 } else {
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63 /* a was negative and |a| < b */
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64 c->used = 1;
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65
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66 /* the result is a single digit */
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67 if (a->used == 1) {
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68 *tmpc++ = b - a->dp[0];
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69 } else {
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70 *tmpc++ = b;
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71 }
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73 /* setup count so the clearing of oldused
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74 * can fall through correctly
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75 */
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76 ix = 1;
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77 }
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78
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79 /* sign always positive */
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80 c->sign = MP_ZPOS;
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81
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82 /* now zero to oldused */
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83 MP_ZERO_DIGITS(tmpc, oldused - ix);
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84 mp_clamp(c);
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85
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86 return MP_OKAY;
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87 }
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89 #endif