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69 lines
1.6 KiB
C
69 lines
1.6 KiB
C
#include <tommath.h>
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#ifdef BN_MP_DIV_2_C
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/* 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@gmail.com, http://math.libtomcrypt.com
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*/
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/* b = a/2 */
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int mp_div_2(mp_int * a, mp_int * b)
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{
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int x, res, oldused;
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/* copy */
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if (b->alloc < a->used) {
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if ((res = mp_grow (b, a->used)) != MP_OKAY) {
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return res;
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}
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}
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oldused = b->used;
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b->used = a->used;
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{
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register mp_digit r, rr, *tmpa, *tmpb;
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/* source alias */
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tmpa = a->dp + b->used - 1;
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/* dest alias */
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tmpb = b->dp + b->used - 1;
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/* carry */
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r = 0;
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for (x = b->used - 1; x >= 0; x--) {
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/* get the carry for the next iteration */
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rr = *tmpa & 1;
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/* shift the current digit, add in carry and store */
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*tmpb-- = (*tmpa-- >> 1) | (r << (DIGIT_BIT - 1));
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/* forward carry to next iteration */
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r = rr;
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}
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/* zero excess digits */
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tmpb = b->dp + b->used;
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for (x = b->used; x < oldused; x++) {
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*tmpb++ = 0;
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}
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}
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b->sign = a->sign;
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mp_clamp (b);
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return MP_OKAY;
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}
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#endif
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/* $Source: /cvs/libtom/libtommath/bn_mp_div_2.c,v $ */
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/* $Revision: 1.3 $ */
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/* $Date: 2006/03/31 14:18:44 $ */
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