56 lines
1.4 KiB
C
56 lines
1.4 KiB
C
#include <tommath.h>
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#ifdef BN_MP_MOD_2D_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://libtom.org
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*/
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/* calc a value mod 2**b */
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int
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mp_mod_2d (mp_int * a, int b, mp_int * c)
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{
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int x, res;
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/* if b is <= 0 then zero the int */
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if (b <= 0) {
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mp_zero (c);
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return MP_OKAY;
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}
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/* if the modulus is larger than the value than return */
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if (b >= (int) (a->used * DIGIT_BIT)) {
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res = mp_copy (a, c);
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return res;
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}
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/* copy */
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if ((res = mp_copy (a, c)) != MP_OKAY) {
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return res;
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}
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/* zero digits above the last digit of the modulus */
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for (x = (b / DIGIT_BIT) + ((b % DIGIT_BIT) == 0 ? 0 : 1); x < c->used; x++) {
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c->dp[x] = 0;
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}
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/* clear the digit that is not completely outside/inside the modulus */
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c->dp[b / DIGIT_BIT] &=
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(mp_digit) ((((mp_digit) 1) << (((mp_digit) b) % DIGIT_BIT)) - ((mp_digit) 1));
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mp_clamp (c);
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return MP_OKAY;
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}
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#endif
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/* $Source$ */
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/* $Revision$ */
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/* $Date$ */
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