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73 lines
1.6 KiB
C
73 lines
1.6 KiB
C
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#include <tommath.h>
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#ifdef BN_MP_RSHD_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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/* shift right a certain amount of digits */
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void mp_rshd (mp_int * a, int b)
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{
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int x;
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/* if b <= 0 then ignore it */
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if (b <= 0) {
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return;
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}
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/* if b > used then simply zero it and return */
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if (a->used <= b) {
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mp_zero (a);
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return;
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}
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{
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register mp_digit *bottom, *top;
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/* shift the digits down */
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/* bottom */
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bottom = a->dp;
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/* top [offset into digits] */
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top = a->dp + b;
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/* this is implemented as a sliding window where
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* the window is b-digits long and digits from
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* the top of the window are copied to the bottom
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*
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* e.g.
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b-2 | b-1 | b0 | b1 | b2 | ... | bb | ---->
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/\ | ---->
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\-------------------/ ---->
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*/
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for (x = 0; x < (a->used - b); x++) {
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*bottom++ = *top++;
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}
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/* zero the top digits */
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for (; x < a->used; x++) {
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*bottom++ = 0;
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}
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}
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/* remove excess digits */
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a->used -= b;
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}
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#endif
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/* $Source: /cvs/libtom/libtommath/bn_mp_rshd.c,v $ */
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/* $Revision: 1.3 $ */
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/* $Date: 2006/03/31 14:18:44 $ */
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