73 lines
1.7 KiB
C
73 lines
1.7 KiB
C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
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*
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* LibTomMath is a library that provides multiple-precision
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* integer arithmetic as well as number theoretic functionality.
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*
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* The library was designed directly after the MPI library by
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* Michael Fromberger but has been written from scratch with
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* additional optimizations in place.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
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*/
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#include <tommath.h>
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/* multiply by a digit */
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int
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mp_mul_d (mp_int * a, mp_digit b, mp_int * c)
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{
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int res, pa, olduse;
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/* make sure c is big enough to hold a*b */
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pa = a->used;
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if (c->alloc < pa + 1) {
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if ((res = mp_grow (c, pa + 1)) != MP_OKAY) {
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return res;
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}
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}
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/* get the original destinations used count */
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olduse = c->used;
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/* set the new temporary used count */
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c->used = pa + 1;
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c->sign = a->sign;
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{
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register mp_digit u, *tmpa, *tmpc;
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register mp_word r;
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register int ix;
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/* alias for a->dp [source] */
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tmpa = a->dp;
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/* alias for c->dp [dest] */
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tmpc = c->dp;
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/* zero carry */
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u = 0;
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for (ix = 0; ix < pa; ix++) {
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/* compute product and carry sum for this term */
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r = ((mp_word) u) + ((mp_word)*tmpa++) * ((mp_word)b);
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/* mask off higher bits to get a single digit */
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*tmpc++ = (mp_digit) (r & ((mp_word) MP_MASK));
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/* send carry into next iteration */
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u = (mp_digit) (r >> ((mp_word) DIGIT_BIT));
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}
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/* store final carry [if any] */
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*tmpc++ = u;
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/* now zero digits above the top */
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for (; pa < olduse; pa++) {
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*tmpc++ = 0;
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}
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}
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mp_clamp (c);
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return MP_OKAY;
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}
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