tommath/bn_mp_2expt.c

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#include "tommath_private.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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* LibTomMath is a library that provides multiple-precision
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* integer arithmetic as well as number theoretic functionality.
*
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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
* additional optimizations in place.
*
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* SPDX-License-Identifier: Unlicense
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*/
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/* computes a = 2**b
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*
* Simple algorithm which zeroes the int, grows it then just sets one bit
* as required.
*/
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int 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 */
mp_zero(a);
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/* grow a to accomodate the single bit */
if ((res = mp_grow(a, (b / DIGIT_BIT) + 1)) != MP_OKAY) {
return res;
}
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/* set the used count of where the bit will go */
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 << (mp_digit)(b % DIGIT_BIT);
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return MP_OKAY;
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}
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#endif
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/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */