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kc3-lang/libtommath/bn_mp_reduce_2k_setup.c

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  • Author : Tom St Denis
    Date : 2004-10-29 22:07:18
    Hash : e549ccfe
    Message : added libtommath-0.32

  • bn_mp_reduce_2k_setup.c
  • #include <tommath.h>
    #ifdef BN_MP_REDUCE_2K_SETUP_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.
     *
     * The library is free for all purposes without any express
     * guarantee it works.
     *
     * Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
     */
    
    /* determines the setup value */
    int 
    mp_reduce_2k_setup(mp_int *a, mp_digit *d)
    {
       int res, p;
       mp_int tmp;
       
       if ((res = mp_init(&tmp)) != MP_OKAY) {
          return res;
       }
       
       p = mp_count_bits(a);
       if ((res = mp_2expt(&tmp, p)) != MP_OKAY) {
          mp_clear(&tmp);
          return res;
       }
       
       if ((res = s_mp_sub(&tmp, a, &tmp)) != MP_OKAY) {
          mp_clear(&tmp);
          return res;
       }
       
       *d = tmp.dp[0];
       mp_clear(&tmp);
       return MP_OKAY;
    }
    #endif