bn_mp_expt_u32.c

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Author : Francois Perrad
Date : 2019-05-29 12:23:08
Hash : a402b462
Message : refactor with goto

bn_mp_expt_u32.c

#include "tommath_private.h"
#ifdef BN_MP_EXPT_U32_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */

/* calculate c = a**b  using a square-multiply algorithm */
mp_err mp_expt_u32(const mp_int *a, uint32_t b, mp_int *c)
{
   mp_err err;

   mp_int  g;

   if ((err = mp_init_copy(&g, a)) != MP_OKAY) {
      return err;
   }

   /* set initial result */
   mp_set(c, 1uL);

   while (b > 0u) {
      /* if the bit is set multiply */
      if ((b & 1u) != 0u) {
         if ((err = mp_mul(c, &g, c)) != MP_OKAY) {
            goto LBL_ERR;
         }
      }

      /* square */
      if (b > 1u) {
         if ((err = mp_sqr(&g, &g)) != MP_OKAY) {
            goto LBL_ERR;
         }
      }

      /* shift to next bit */
      b >>= 1;
   }

   err = MP_OKAY;

LBL_ERR:
   mp_clear(&g);
   return err;
}

#endif

kc3-lang/libtommath/bn_mp_expt_u32.c

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