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glibc  2.9
Functions
divrem.c File Reference
#include <gmp.h>
#include "gmp-impl.h"
#include "longlong.h"

Go to the source code of this file.

Functions

mp_limb_t mpn_divrem (mp_ptr qp, mp_size_t qextra_limbs, mp_ptr np, mp_size_t nsize, mp_srcptr dp, mp_size_t dsize)

Function Documentation

mp_limb_t mpn_divrem ( mp_ptr  qp,
mp_size_t  qextra_limbs,
mp_ptr  np,
mp_size_t  nsize,
mp_srcptr  dp,
mp_size_t  dsize 
)

Definition at line 49 of file divrem.c.

{
  mp_limb_t most_significant_q_limb = 0;

  switch (dsize)
    {
    case 0:
      /* We are asked to divide by zero, so go ahead and do it!  (To make
        the compiler not remove this statement, return the value.)  */
      return 1 / dsize;

    case 1:
      {
       mp_size_t i;
       mp_limb_t n1;
       mp_limb_t d;

       d = dp[0];
       n1 = np[nsize - 1];

       if (n1 >= d)
         {
           n1 -= d;
           most_significant_q_limb = 1;
         }

       qp += qextra_limbs;
       for (i = nsize - 2; i >= 0; i--)
         udiv_qrnnd (qp[i], n1, n1, np[i], d);
       qp -= qextra_limbs;

       for (i = qextra_limbs - 1; i >= 0; i--)
         udiv_qrnnd (qp[i], n1, n1, 0, d);

       np[0] = n1;
      }
      break;

    case 2:
      {
       mp_size_t i;
       mp_limb_t n1, n0, n2;
       mp_limb_t d1, d0;

       np += nsize - 2;
       d1 = dp[1];
       d0 = dp[0];
       n1 = np[1];
       n0 = np[0];

       if (n1 >= d1 && (n1 > d1 || n0 >= d0))
         {
           sub_ddmmss (n1, n0, n1, n0, d1, d0);
           most_significant_q_limb = 1;
         }

       for (i = qextra_limbs + nsize - 2 - 1; i >= 0; i--)
         {
           mp_limb_t q;
           mp_limb_t r;

           if (i >= qextra_limbs)
             np--;
           else
             np[0] = 0;

           if (n1 == d1)
             {
              /* Q should be either 111..111 or 111..110.  Need special
                 treatment of this rare case as normal division would
                 give overflow.  */
              q = ~(mp_limb_t) 0;

              r = n0 + d1;
              if (r < d1)   /* Carry in the addition? */
                {
                  add_ssaaaa (n1, n0, r - d0, np[0], 0, d0);
                  qp[i] = q;
                  continue;
                }
              n1 = d0 - (d0 != 0);
              n0 = -d0;
             }
           else
             {
              udiv_qrnnd (q, r, n1, n0, d1);
              umul_ppmm (n1, n0, d0, q);
             }

           n2 = np[0];
         q_test:
           if (n1 > r || (n1 == r && n0 > n2))
             {
              /* The estimated Q was too large.  */
              q--;

              sub_ddmmss (n1, n0, n1, n0, 0, d0);
              r += d1;
              if (r >= d1)  /* If not carry, test Q again.  */
                goto q_test;
             }

           qp[i] = q;
           sub_ddmmss (n1, n0, r, n2, n1, n0);
         }
       np[1] = n1;
       np[0] = n0;
      }
      break;

    default:
      {
       mp_size_t i;
       mp_limb_t dX, d1, n0;

       np += nsize - dsize;
       dX = dp[dsize - 1];
       d1 = dp[dsize - 2];
       n0 = np[dsize - 1];

       if (n0 >= dX)
         {
           if (n0 > dX || mpn_cmp (np, dp, dsize - 1) >= 0)
             {
              mpn_sub_n (np, np, dp, dsize);
              n0 = np[dsize - 1];
              most_significant_q_limb = 1;
             }
         }

       for (i = qextra_limbs + nsize - dsize - 1; i >= 0; i--)
         {
           mp_limb_t q;
           mp_limb_t n1, n2;
           mp_limb_t cy_limb;

           if (i >= qextra_limbs)
             {
              np--;
              n2 = np[dsize];
             }
           else
             {
              n2 = np[dsize - 1];
              MPN_COPY_DECR (np + 1, np, dsize);
              np[0] = 0;
             }

           if (n0 == dX)
             /* This might over-estimate q, but it's probably not worth
               the extra code here to find out.  */
             q = ~(mp_limb_t) 0;
           else
             {
              mp_limb_t r;

              udiv_qrnnd (q, r, n0, np[dsize - 1], dX);
              umul_ppmm (n1, n0, d1, q);

              while (n1 > r || (n1 == r && n0 > np[dsize - 2]))
                {
                  q--;
                  r += dX;
                  if (r < dX)      /* I.e. "carry in previous addition?"  */
                    break;
                  n1 -= n0 < d1;
                  n0 -= d1;
                }
             }

           /* Possible optimization: We already have (q * n0) and (1 * n1)
              after the calculation of q.  Taking advantage of that, we
              could make this loop make two iterations less.  */

           cy_limb = mpn_submul_1 (np, dp, dsize, q);

           if (n2 != cy_limb)
             {
              mpn_add_n (np, np, dp, dsize);
              q--;
             }

           qp[i] = q;
           n0 = np[dsize - 1];
         }
      }
    }

  return most_significant_q_limb;
}

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