Mercurial > dropbear

annotate libtommath/bn_mp_div_d.c @ 1734:73646de50f13 DROPBEAR_2020.80

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version 2020.80
author Matt Johnston <matt@ucc.asn.au>
date Fri, 26 Jun 2020 21:45:59 +0800
parents 1051e4eea25a
children
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rev   line source
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_DIV_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 division (based on routine from MPI) */
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7 mp_err mp_div_d(const mp_int *a, mp_digit b, mp_int *c, mp_digit *d)
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8 {
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9 mp_int q;
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10 mp_word w;
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11 mp_digit t;
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12 mp_err err;
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13 int ix;
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14
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15 /* cannot divide by zero */
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16 if (b == 0u) {
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17 return MP_VAL;
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18 }
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19
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20 /* quick outs */
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21 if ((b == 1u) || MP_IS_ZERO(a)) {
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22 if (d != NULL) {
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23 *d = 0;
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24 }
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25 if (c != NULL) {
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26 return mp_copy(a, c);
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27 }
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28 return MP_OKAY;
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29 }
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30
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31 /* power of two ? */
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32 if ((b & (b - 1u)) == 0u) {
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33 ix = 1;
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34 while ((ix < MP_DIGIT_BIT) && (b != (((mp_digit)1)<<ix))) {
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35 ix++;
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36 }
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37 if (d != NULL) {
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38 *d = a->dp[0] & (((mp_digit)1<<(mp_digit)ix) - 1uL);
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39 }
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40 if (c != NULL) {
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41 return mp_div_2d(a, ix, c, NULL);
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42 }
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43 return MP_OKAY;
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44 }
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45
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46 /* three? */
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47 if (MP_HAS(MP_DIV_3) && (b == 3u)) {
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48 return mp_div_3(a, c, d);
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49 }
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50
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51 /* no easy answer [c'est la vie]. Just division */
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52 if ((err = mp_init_size(&q, a->used)) != MP_OKAY) {
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53 return err;
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54 }
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56 q.used = a->used;
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57 q.sign = a->sign;
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58 w = 0;
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59 for (ix = a->used - 1; ix >= 0; ix--) {
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60 w = (w << (mp_word)MP_DIGIT_BIT) | (mp_word)a->dp[ix];
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61
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62 if (w >= b) {
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63 t = (mp_digit)(w / b);
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64 w -= (mp_word)t * (mp_word)b;
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65 } else {
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66 t = 0;
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67 }
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68 q.dp[ix] = t;
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69 }
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70
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71 if (d != NULL) {
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72 *d = (mp_digit)w;
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73 }
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74
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75 if (c != NULL) {
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76 mp_clamp(&q);
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77 mp_exch(&q, c);
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78 }
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79 mp_clear(&q);
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80
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81 return err;
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82 }
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84 #endif