/* UltraSPARC 64 mpn_divexact_1 -- mpn by limb exact division.

   THE FUNCTIONS IN THIS FILE ARE FOR INTERNAL USE ONLY.  THEY'RE ALMOST

   CERTAIN TO BE SUBJECT TO INCOMPATIBLE CHANGES OR DISAPPEAR COMPLETELY IN

   FUTURE GNU MP RELEASES.

Copyright 2000, 2001, 2003 Free Software Foundation, Inc.

This file is part of the GNU MP Library.

The GNU MP Library is free software; you can redistribute it and/or modify

it under the terms of either:

  * the GNU Lesser General Public License as published by the Free

    Software Foundation; either version 3 of the License, or (at your

    option) any later version.

or

  * the GNU General Public License as published by the Free Software

    Foundation; either version 2 of the License, or (at your option) any

    later version.

or both in parallel, as here.

The GNU MP Library is distributed in the hope that it will be useful, but

WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY

or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

for more details.

You should have received copies of the GNU General Public License and the

GNU Lesser General Public License along with the GNU MP Library.  If not,

see https://www.gnu.org/licenses/.  */

#include "gmp.h"

#include "gmp-impl.h"

#include "longlong.h"

#include "mpn/sparc64/sparc64.h"

/*                 64-bit divisor   32-bit divisor

                    cycles/limb      cycles/limb

                     (approx)         (approx)

   Ultrasparc 2i:      110               70

*/

/* There are two key ideas here to reduce mulx's.  Firstly when the divisor

   is 32-bits the high of q*d can be calculated without the two 32x32->64

   cross-products involving the high 32-bits of the divisor, that being zero

   of course.  Secondly umul_ppmm_lowequal and umul_ppmm_half_lowequal save

   one mulx (each) knowing the low of q*d is equal to the input limb l.

   For size==1, a simple udivx is used.  This is faster than calculating an

   inverse.

   For a 32-bit divisor and small sizes, an attempt was made at a simple

   udivx loop (two per 64-bit limb), but it turned out to be slower than

   mul-by-inverse.  At size==2 the inverse is about 260 cycles total

   compared to a udivx at 291.  Perhaps the latter would suit when size==2

   but the high 32-bits of the second limb is zero (saving one udivx), but

   it doesn't seem worth a special case just for that.  */

void

mpn_divexact_1 (mp_ptr dst, mp_srcptr src, mp_size_t size, mp_limb_t divisor)

{

  mp_limb_t  inverse, s, s_next, c, l, ls, q;

  unsigned   rshift, lshift;

  mp_limb_t  lshift_mask;

  mp_limb_t  divisor_h;

  ASSERT (size >= 1);

  ASSERT (divisor != 0);

  ASSERT (MPN_SAME_OR_SEPARATE_P (dst, src, size));

  ASSERT_MPN (src, size);

  ASSERT_LIMB (divisor);

  s = *src++;                 /* src low limb */

  size--;

  if (size == 0)

    {

      *dst = s / divisor;

      return;

    }

  if ((divisor & 1) == 0)

    {

      count_trailing_zeros (rshift, divisor);

      divisor >>= rshift;

    }

  else

    rshift = 0;

  binvert_limb (inverse, divisor);

  lshift = 64 - rshift;

  /* lshift==64 means no shift, so must mask out other part in this case */

  lshift_mask = (rshift == 0 ? 0 : MP_LIMB_T_MAX);

  c = 0;

  divisor_h = HIGH32 (divisor);

  if (divisor_h == 0)

    {

      /* 32-bit divisor */

      do

        {

          s_next = *src++;

          ls = (s >> rshift) | ((s_next << lshift) & lshift_mask);

          s = s_next;

          SUBC_LIMB (c, l, ls, c);

          q = l * inverse;

          *dst++ = q;

          umul_ppmm_half_lowequal (l, q, divisor, l);

          c += l;

          size--;

        }

      while (size != 0);

      ls = s >> rshift;

      l = ls - c;

      q = l * inverse;

      *dst = q;

    }

  else

    {

      /* 64-bit divisor */

      mp_limb_t  divisor_l = LOW32 (divisor);

      do

        {

          s_next = *src++;

          ls = (s >> rshift) | ((s_next << lshift) & lshift_mask);

          s = s_next;

          SUBC_LIMB (c, l, ls, c);

          q = l * inverse;

          *dst++ = q;

          umul_ppmm_lowequal (l, q, divisor, divisor_h, divisor_l, l);

          c += l;

          size--;

        }

      while (size != 0);

      ls = s >> rshift;

      l = ls - c;

      q = l * inverse;

      *dst = q;

    }

}