annotate libtommath/bn_mp_mul_d.c @ 1934:83b6a47759a8

Add m_snprintf() that won't return negative
author Matt Johnston <matt@ucc.asn.au>
date Fri, 01 Apr 2022 12:10:48 +0800
parents 1051e4eea25a
children
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1 #include "tommath_private.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 /* SPDX-License-Identifier: Unlicense */
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6 /* multiply by a digit */
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7 mp_err mp_mul_d(const mp_int *a, mp_digit b, mp_int *c)
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8 {
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9 mp_digit u, *tmpa, *tmpc;
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10 mp_word r;
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11 mp_err err;
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12 int ix, olduse;
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13
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14 /* make sure c is big enough to hold a*b */
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15 if (c->alloc < (a->used + 1)) {
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16 if ((err = mp_grow(c, a->used + 1)) != MP_OKAY) {
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17 return err;
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18 }
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19 }
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21 /* get the original destinations used count */
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22 olduse = c->used;
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24 /* set the sign */
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25 c->sign = a->sign;
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27 /* alias for a->dp [source] */
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28 tmpa = a->dp;
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30 /* alias for c->dp [dest] */
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31 tmpc = c->dp;
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33 /* zero carry */
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34 u = 0;
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36 /* compute columns */
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37 for (ix = 0; ix < a->used; ix++) {
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38 /* compute product and carry sum for this term */
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39 r = (mp_word)u + ((mp_word)*tmpa++ * (mp_word)b);
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41 /* mask off higher bits to get a single digit */
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42 *tmpc++ = (mp_digit)(r & (mp_word)MP_MASK);
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44 /* send carry into next iteration */
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45 u = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT);
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46 }
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48 /* store final carry [if any] and increment ix offset */
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49 *tmpc++ = u;
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50 ++ix;
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52 /* now zero digits above the top */
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53 MP_ZERO_DIGITS(tmpc, olduse - ix);
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54
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55 /* set used count */
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56 c->used = a->used + 1;
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57 mp_clamp(c);
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59 return MP_OKAY;
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60 }
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61 #endif