bn_mp_2expt.c 1.15 KB
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#include "tommath_private.h"
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#ifdef BN_MP_2EXPT_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
 *
 * LibTomMath is a library that provides multiple-precision
 * integer arithmetic as well as number theoretic functionality.
 *
 * The library was designed directly after the MPI library by
 * 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 */
   a->dp[b / DIGIT_BIT] = (mp_digit)1 << (mp_digit)(b % DIGIT_BIT);
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   return MP_OKAY;
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}
#endif

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/* ref:         HEAD -> master, tag: v1.1.0 */
/* git commit:  08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
/* commit time: 2019-01-28 20:32:32 +0100 */