tomsfastmath/src/exptmod/fp_2expt.c

/* TomsFastMath, a fast ISO C bignum library.
 * 
 * This project is meant to fill in where LibTomMath
 * falls short.  That is speed ;-)
 *
 * This project is public domain and free for all purposes.
 * 
 * Tom St Denis, tomstdenis@gmail.com
 */
#include <tfm_private.h>

/* computes a = 2**b */
void fp_2expt(fp_int *a, int b)
{
   int     z;

   /* zero a as per default */
   fp_zero (a);

   if (b < 0) { 
      return;
   }

   z = b / DIGIT_BIT;
   if (z >= FP_SIZE) {
      return; 
   }

  /* set the used count of where the bit will go */
  a->used = z + 1;

  /* put the single bit in its place */
  a->dp[z] = ((fp_digit)1) << (b % DIGIT_BIT);
}


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