bn_mp_div_2d.c

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Author : Tom St Denis
Date : 2003-02-28 16:08:34
Hash : 57354e11
Message : added libtommath-0.12

bn_mp_div_2d.c

/* LibTomMath, multiple-precision integer library -- Tom St Denis
 *
 * LibTomMath is library that provides for multiple-precision
 * integer arithmetic as well as number theoretic functionality.
 *
 * The library is 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://libtommath.iahu.ca
 */
#include <tommath.h>

/* shift right by a certain bit count (store quotient in c, remainder in d) */
int
mp_div_2d (mp_int * a, int b, mp_int * c, mp_int * d)
{
  mp_digit  D, r, rr;
  int       x, res;
  mp_int    t;


  /* if the shift count is <= 0 then we do no work */
  if (b <= 0) {
    res = mp_copy (a, c);
    if (d != NULL) {
      mp_zero (d);
    }
    return res;
  }

  if ((res = mp_init (&t)) != MP_OKAY) {
    return res;
  }

  /* get the remainder */
  if (d != NULL) {
    if ((res = mp_mod_2d (a, b, &t)) != MP_OKAY) {
      mp_clear (&t);
      return res;
    }
  }

  /* copy */
  if ((res = mp_copy (a, c)) != MP_OKAY) {
    mp_clear (&t);
    return res;
  }

  /* shift by as many digits in the bit count */
  mp_rshd (c, b / DIGIT_BIT);

  /* shift any bit count < DIGIT_BIT */
  D = (mp_digit) (b % DIGIT_BIT);
  if (D != 0) {
    r = 0;
    for (x = c->used - 1; x >= 0; x--) {
      /* get the lower  bits of this word in a temp */
      rr = c->dp[x] & ((mp_digit) ((1U << D) - 1U));

      /* shift the current word and mix in the carry bits from the previous word */
      c->dp[x] = (c->dp[x] >> D) | (r << (DIGIT_BIT - D));

      /* set the carry to the carry bits of the current word found above */
      r = rr;
    }
  }
  mp_clamp (c);
  res = MP_OKAY;
  if (d != NULL) {
    mp_exch (&t, d);
  }
  mp_clear (&t);
  return MP_OKAY;
}

kc3-lang/libtommath/bn_mp_div_2d.c

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kc3-lang/libtommath /bn_mp_div_2d.c