gcc/gmp/mpn/cray/ieee/mul_1.c

/* Cray PVP/IEEE mpn_mul_1 -- multiply a limb vector with a limb and store the
   result in a second limb vector.

Copyright 2000, 2001 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 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.

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 Lesser General Public
License for more details.

You should have received a copy of the GNU Lesser General Public License
along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */

/* This code runs at 5 cycles/limb on a T90.  That would probably
   be hard to improve upon, even with assembly code.  */

#include <intrinsics.h>
#include "gmp.h"
#include "gmp-impl.h"

mp_limb_t
mpn_mul_1 (mp_ptr rp, mp_srcptr up, mp_size_t n, mp_limb_t vl)
{
  mp_limb_t cy[n];
  mp_limb_t a, b, r, s0, s1, c0, c1;
  mp_size_t i;
  int more_carries;

  if (up == rp)
    {
      /* The algorithm used below cannot handle overlap.  Handle it here by
	 making a temporary copy of the source vector, then call ourselves.  */
      mp_limb_t xp[n];
      MPN_COPY (xp, up, n);
      return mpn_mul_1 (rp, xp, n, vl);
    }

  a = up[0] * vl;
  rp[0] = a;
  cy[0] = 0;

  /* Main multiply loop.  Generate a raw accumulated output product in rp[]
     and a carry vector in cy[].  */
#pragma _CRI ivdep
  for (i = 1; i < n; i++)
    {
      a = up[i] * vl;
      b = _int_mult_upper (up[i - 1], vl);
      s0 = a + b;
      c0 = ((a & b) | ((a | b) & ~s0)) >> 63;
      rp[i] = s0;
      cy[i] = c0;
    }
  /* Carry add loop.  Add the carry vector cy[] to the raw sum rp[] and
     store the new sum back to rp[0].  */
  more_carries = 0;
#pragma _CRI ivdep
  for (i = 2; i < n; i++)
    {
      r = rp[i];
      c0 = cy[i - 1];
      s0 = r + c0;
      rp[i] = s0;
      c0 = (r & ~s0) >> 63;
      more_carries += c0;
    }
  /* If that second loop generated carry, handle that in scalar loop.  */
  if (more_carries)
    {
      mp_limb_t cyrec = 0;
      /* Look for places where rp[k] is zero and cy[k-1] is non-zero.
	 These are where we got a recurrency carry.  */
      for (i = 2; i < n; i++)
	{
	  r = rp[i];
	  c0 = (r == 0 && cy[i - 1] != 0);
	  s0 = r + cyrec;
	  rp[i] = s0;
	  c1 = (r & ~s0) >> 63;
	  cyrec = c0 | c1;
	}
      return _int_mult_upper (up[n - 1], vl) + cyrec + cy[n - 1];
    }

  return _int_mult_upper (up[n - 1], vl) + cy[n - 1];
}