45 lines
1.1 KiB
C
45 lines
1.1 KiB
C
#include <tommath.h>
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#ifdef BN_MP_2EXPT_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@iahu.ca, http://math.libtomcrypt.org
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*/
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/* computes a = 2**b
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*
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* Simple algorithm which zeroes the int, grows it then just sets one bit
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* as required.
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*/
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int
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mp_2expt (mp_int * a, int b)
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{
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int res;
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/* zero a as per default */
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mp_zero (a);
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/* grow a to accomodate the single bit */
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if ((res = mp_grow (a, b / DIGIT_BIT + 1)) != MP_OKAY) {
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return res;
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}
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/* set the used count of where the bit will go */
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a->used = b / DIGIT_BIT + 1;
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/* put the single bit in its place */
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a->dp[b / DIGIT_BIT] = ((mp_digit)1) << (b % DIGIT_BIT);
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return MP_OKAY;
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}
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#endif
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