mpir/mpn/generic/mul_n.c

/* mpn_mul_n and helper function -- Multiply/square natural numbers.

   THE HELPER FUNCTIONS IN THIS FILE (meaning everything except mpn_mul_n)
   ARE INTERNAL FUNCTIONS WITH MUTABLE INTERFACES.  IT IS ONLY SAFE TO REACH
   THEM THROUGH DOCUMENTED INTERFACES.  IN FACT, IT IS ALMOST GUARANTEED
   THAT THEY'LL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.


Copyright 1991, 1993, 1994, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
2005, Free Software Foundation, Inc.

Copyright 2009 Jason Moxham
Copyright 2009 William Hart

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 2.1 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; see the file COPYING.LIB.  If not, write to
the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
MA 02110-1301, USA. */

#include "mpir.h"
#include "gmp-impl.h"
#include "longlong.h"


/* Multiplies using 3 half-sized mults and so on recursively.
 * p[0..2*n-1] := product of a[0..n-1] and b[0..n-1].
 * No overlap of p[...] with a[...] or b[...].
 * ws is workspace.
 */

void
mpn_kara_mul_n (mp_ptr p, mp_srcptr a, mp_srcptr b, mp_size_t n, mp_ptr ws)
{
  mp_limb_t w, w0, w1,c;
  mp_size_t n2;
  mp_srcptr x, y;
  mp_size_t i;
  int sign, ci;

  n2 = n >> 1;
  ASSERT (n2 > 0);

  if ((n & 1) != 0)
    {
      /* Odd length. */
      mp_size_t n1, n3, nm1;

      n3 = n - n2;

      sign = 0;
      w = a[n2];
      if (w != 0)
	w -= mpn_sub_n (p, a, a + n3, n2);
      else
	{
	  i = n2;
	  do
	    {
	      --i;
	      w0 = a[i];
	      w1 = a[n3 + i];
	    }
	  while (w0 == w1 && i != 0);
	  if (w0 < w1)
	    {
	      x = a + n3;
	      y = a;
	      sign = ~0;
	    }
	  else
	    {
	      x = a;
	      y = a + n3;
	    }
	  mpn_sub_n (p, x, y, n2);
	}
      p[n2] = w;

      w = b[n2];
      if (w != 0)
	w -= mpn_sub_n (p + n3, b, b + n3, n2);
      else
	{
	  i = n2;
	  do
	    {
	      --i;
	      w0 = b[i];
	      w1 = b[n3 + i];
	    }
	  while (w0 == w1 && i != 0);
	  if (w0 < w1)
	    {
	      x = b + n3;
	      y = b;
	      sign = ~sign;
	    }
	  else
	    {
	      x = b;
	      y = b + n3;
	    }
	  mpn_sub_n (p + n3, x, y, n2);
	}
      p[n] = w;

      n1 = n + 1;
      if (n2 < MUL_KARATSUBA_THRESHOLD)
	{
	  if (n3 < MUL_KARATSUBA_THRESHOLD)
	    {
	      mpn_mul_basecase (ws, p, n3, p + n3, n3);
	      mpn_mul_basecase (p, a, n3, b, n3);
	    }
	  else
	    {
	      mpn_kara_mul_n (ws, p, p + n3, n3, ws + n1);
	      mpn_kara_mul_n (p, a, b, n3, ws + n1);
	    }
	  mpn_mul_basecase (p + n1, a + n3, n2, b + n3, n2);
	}
      else
	{
	  mpn_kara_mul_n (ws, p, p + n3, n3, ws + n1);
	  mpn_kara_mul_n (p, a, b, n3, ws + n1);
	  mpn_kara_mul_n (p + n1, a + n3, b + n3, n2, ws + n1);
	}

      nm1 = n - 1;
      if (sign)
	{
	 #if HAVE_NATIVE_mpn_addadd_n
	   c=mpn_addadd_n(ws,p+n1,p,ws,nm1);
  	   #if GMP_NAIL_BITS==0
  	     add_ssaaaa(ws[n],ws[nm1],ws[n],ws[nm1],p[n],p[nm1]);
  	     add_ssaaaa(ws[n],ws[nm1],ws[n],ws[nm1],0,c);
  	   #else
  	     mpn_add_n(ws+nm1, p+nm1, ws+nm1 ,2);
  	     mpn_add_1(ws+nm1,ws+nm1,2,c);
  	   #endif
	 #else
	   mpn_add_n (ws, p, ws, n1);
	   c=mpn_add_n (ws, p + n1, ws, nm1);
	   if(c){mp_limb_t x=(ws[nm1]+1) & GMP_NUMB_MASK;ws[nm1]=x;if(x==0)ws[n]=(ws[n]+1) & GMP_NUMB_MASK;}
	 #endif
	}
      else
	{
	 #if HAVE_NATIVE_mpn_addsub_n
           ci=mpn_addsub_n(ws,p+n1,p,ws,nm1);
           #if GMP_NAIL_BITS==0
             sub_ddmmss(ws[n],ws[nm1],p[n],p[nm1],ws[n],ws[nm1]);//mpn_sub_n(ws+nm1,p+nm1,ws+nm1,2);
             if(ci==-1)sub_ddmmss(ws[n],ws[nm1],ws[n],ws[nm1],0,1);//mpn_sub_1(ws+nm1,ws+nm1,2,1);
             if(ci== 1)add_ssaaaa(ws[n],ws[nm1],ws[n],ws[nm1],0,1);//mpn_add_1(ws+nm1,ws+nm1,2,1);
           #else
             mpn_sub_n(ws+nm1,p+nm1,ws+nm1,2);
             if(ci==-1)mpn_sub_1(ws+nm1,ws+nm1,2,1);
             if(ci== 1)mpn_add_1(ws+nm1,ws+nm1,2,1);
           #endif
         #else
	   mpn_sub_n (ws, p, ws, n1);
	   c=mpn_add_n (ws, p + n1, ws, nm1);
	   if(c){mp_limb_t x=(ws[nm1]+1) & GMP_NUMB_MASK;ws[nm1]=x;if(x==0)ws[n]=(ws[n]+1) & GMP_NUMB_MASK;}
         #endif
        }      
      if (mpn_add_n (p + n3, p + n3, ws, n1))
	{
	  mpn_incr_u (p + n1 + n3, 1);
	}
    }
  else
    {
      /* Even length. */
      i = n2;
      do
	{
	  --i;
	  w0 = a[i];
	  w1 = a[n2 + i];
	}
      while (w0 == w1 && i != 0);
      sign = 0;
      if (w0 < w1)
	{
	  x = a + n2;
	  y = a;
	  sign = ~0;
	}
      else
	{
	  x = a;
	  y = a + n2;
	}
      mpn_sub_n (p, x, y, n2);

      i = n2;
      do
	{
	  --i;
	  w0 = b[i];
	  w1 = b[n2 + i];
	}
      while (w0 == w1 && i != 0);
      if (w0 < w1)
	{
	  x = b + n2;
	  y = b;
	  sign = ~sign;
	}
      else
	{
	  x = b;
	  y = b + n2;
	}
      mpn_sub_n (p + n2, x, y, n2);

      /* Pointwise products. */
      if (n2 < MUL_KARATSUBA_THRESHOLD)
	{
	  mpn_mul_basecase (ws, p, n2, p + n2, n2);
	  mpn_mul_basecase (p, a, n2, b, n2);
	  mpn_mul_basecase (p + n, a + n2, n2, b + n2, n2);
	}
      else
	{
	  mpn_kara_mul_n (ws, p, p + n2, n2, ws + n);
	  mpn_kara_mul_n (p, a, b, n2, ws + n);
	  mpn_kara_mul_n (p + n, a + n2, b + n2, n2, ws + n);
	}

      /* Interpolate. */
          
      if (sign)
	{
	 #if HAVE_NATIVE_mpn_addadd_n
	 w=mpn_addadd_n(ws,p+n,p,ws,n);
	 #else 
	 w = mpn_add_n (ws, p, ws, n);
         w += mpn_add_n (ws, p + n, ws, n);
         #endif
        }
      else
	{
	 #if HAVE_NATIVE_mpn_addsub_n
	 w=mpn_addsub_n(ws,p+n,p,ws,n);
	 #else
	 w = -mpn_sub_n (ws, p, ws, n);
         w += mpn_add_n (ws, p + n, ws, n);
         #endif         
        }
     
      w += mpn_add_n (p + n2, p + n2, ws, n);
      MPN_INCR_U (p + n2 + n, 2 * n - (n2 + n), w);
    }
}

void
mpn_kara_sqr_n (mp_ptr p, mp_srcptr a, mp_size_t n, mp_ptr ws)
{
  mp_limb_t w, w0, w1, c;
  int ci;
  mp_size_t n2;
  mp_srcptr x, y;
  mp_size_t i;

  n2 = n >> 1;
  ASSERT (n2 > 0);

  if ((n & 1) != 0)
    {
      /* Odd length. */
      mp_size_t n1, n3, nm1;

      n3 = n - n2;

      w = a[n2];
      if (w != 0)
	w -= mpn_sub_n (p, a, a + n3, n2);
      else
	{
	  i = n2;
	  do
	    {
	      --i;
	      w0 = a[i];
	      w1 = a[n3 + i];
	    }
	  while (w0 == w1 && i != 0);
	  if (w0 < w1)
	    {
	      x = a + n3;
	      y = a;
	    }
	  else
	    {
	      x = a;
	      y = a + n3;
	    }
	  mpn_sub_n (p, x, y, n2);
	}
      p[n2] = w;

      n1 = n + 1;

      /* n2 is always either n3 or n3-1 so maybe the two sets of tests here
	 could be combined.  But that's not important, since the tests will
	 take a miniscule amount of time compared to the function calls.  */
      if (BELOW_THRESHOLD (n3, SQR_BASECASE_THRESHOLD))
	{
	  mpn_mul_basecase (ws, p, n3, p, n3);
	  mpn_mul_basecase (p,  a, n3, a, n3);
	}
      else if (BELOW_THRESHOLD (n3, SQR_KARATSUBA_THRESHOLD))
	{
	  mpn_sqr_basecase (ws, p, n3);
	  mpn_sqr_basecase (p,  a, n3);
	}
      else
	{
	  mpn_kara_sqr_n   (ws, p, n3, ws + n1);	 /* (x-y)^2 */
	  mpn_kara_sqr_n   (p,  a, n3, ws + n1);	 /* x^2	    */
	}
      if (BELOW_THRESHOLD (n2, SQR_BASECASE_THRESHOLD))
	mpn_mul_basecase (p + n1, a + n3, n2, a + n3, n2);
      else if (BELOW_THRESHOLD (n2, SQR_KARATSUBA_THRESHOLD))
	mpn_sqr_basecase (p + n1, a + n3, n2);
      else
	mpn_kara_sqr_n   (p + n1, a + n3, n2, ws + n1);	 /* y^2	    */

      /* Since x^2+y^2-(x-y)^2 = 2xy >= 0 there's no need to track the
	 borrow from mpn_sub_n.	 If it occurs then it'll be cancelled by a
	 carry from ws[n].  Further, since 2xy fits in n1 limbs there won't
	 be any carry out of ws[n] other than cancelling that borrow. */

      nm1=n-1;
      #if HAVE_NATIVE_mpn_addsub_n
        ci=mpn_addsub_n(ws,p+n1,p,ws,nm1);
        #if GMP_NAIL_BITS==0
          sub_ddmmss(ws[n],ws[nm1],p[n],p[nm1],ws[n],ws[nm1]);//mpn_sub_n(ws+nm1,p+nm1,ws+nm1,2);
          if(ci==-1)sub_ddmmss(ws[n],ws[nm1],ws[n],ws[nm1],0,1);//mpn_sub_1(ws+nm1,ws+nm1,2,1);
          if(ci==1)add_ssaaaa(ws[n],ws[nm1],ws[n],ws[nm1],0,1);//mpn_add_1(ws+nm1,ws+nm1,2,1);
        #else
          mpn_sub_n(ws+nm1,p+nm1,ws+nm1,2);
          if(ci==-1)mpn_sub_1(ws+nm1,ws+nm1,2,1);
          if(ci==1)mpn_add_1(ws+nm1,ws+nm1,2,1);        
        #endif
      #else
        mpn_sub_n (ws, p, ws, n1);/*   x^2-(x-y)^2   */
        c=mpn_add_n (ws, p + n1, ws, nm1);/*  x^2+y^2-(x-y)^2 = 2xy    */
        if(c){mp_limb_t x = (ws[nm1] + 1) & GMP_NUMB_MASK;ws[nm1] = x; if (x == 0) ws[n] = (ws[n] + 1) & GMP_NUMB_MASK;}
      #endif

      if (mpn_add_n (p + n3, p + n3, ws, n1))
	{
	  mpn_incr_u (p + n1 + n3, 1);
	}
    }
  else
    {
      /* Even length. */
      i = n2;
      do
	{
	  --i;
	  w0 = a[i];
	  w1 = a[n2 + i];
	}
      while (w0 == w1 && i != 0);
      if (w0 < w1)
	{
	  x = a + n2;
	  y = a;
	}
      else
	{
	  x = a;
	  y = a + n2;
	}
      mpn_sub_n (p, x, y, n2);

      /* Pointwise products. */
      if (BELOW_THRESHOLD (n2, SQR_BASECASE_THRESHOLD))
	{
	  mpn_mul_basecase (ws,    p,      n2, p,      n2);
	  mpn_mul_basecase (p,     a,      n2, a,      n2);
	  mpn_mul_basecase (p + n, a + n2, n2, a + n2, n2);
	}
      else if (BELOW_THRESHOLD (n2, SQR_KARATSUBA_THRESHOLD))
	{
	  mpn_sqr_basecase (ws,    p,      n2);
	  mpn_sqr_basecase (p,     a,      n2);
	  mpn_sqr_basecase (p + n, a + n2, n2);
	}
      else
	{
	  mpn_kara_sqr_n (ws,    p,      n2, ws + n);
	  mpn_kara_sqr_n (p,     a,      n2, ws + n);
	  mpn_kara_sqr_n (p + n, a + n2, n2, ws + n);
	}

      /* Interpolate. */
      #if HAVE_NATIVE_mpn_addsub_n
      w=mpn_addsub_n(ws,p+n,p,ws,n);      
      #else      
      w = -mpn_sub_n (ws, p, ws, n);
      w += mpn_add_n (ws, p + n, ws, n);
      #endif
      w += mpn_add_n (p + n2, p + n2, ws, n);
      MPN_INCR_U (p + n2 + n, 2 * n - (n2 + n), w);
    }
}

void
mpn_mul_n (mp_ptr p, mp_srcptr a, mp_srcptr b, mp_size_t n)
{
  ASSERT (n >= 1);
  ASSERT (! MPN_OVERLAP_P (p, 2 * n, a, n));
  ASSERT (! MPN_OVERLAP_P (p, 2 * n, b, n));

  if (BELOW_THRESHOLD (n, MUL_KARATSUBA_THRESHOLD))
    {
      mpn_mul_basecase (p, a, n, b, n);
    }
  else if (BELOW_THRESHOLD (n, MUL_TOOM3_THRESHOLD))
    {
      /* Allocate workspace of fixed size on stack: fast! */
      mp_limb_t ws[MPN_KARA_MUL_N_TSIZE (MUL_TOOM3_THRESHOLD_LIMIT-1)];
      ASSERT (MUL_TOOM3_THRESHOLD <= MUL_TOOM3_THRESHOLD_LIMIT);
      mpn_kara_mul_n (p, a, b, n, ws);
    }
  else if (BELOW_THRESHOLD (n, MUL_TOOM4_THRESHOLD))
    {
      mp_ptr ws;
      TMP_SDECL;
      TMP_SMARK;
      ws = TMP_SALLOC_LIMBS (MPN_TOOM3_MUL_N_TSIZE (n));
      mpn_toom3_mul_n (p, a, b, n, ws);
      TMP_SFREE;
    }
  else if (BELOW_THRESHOLD (n, MUL_TOOM8H_THRESHOLD))
    {
       mpn_toom4_mul_n (p, a, b, n);
    }
#if WANT_FFT || TUNE_PROGRAM_BUILD
  else if (BELOW_THRESHOLD (n, MUL_FFT_FULL_THRESHOLD))
    {
       mpn_toom8h_mul (p, a, n, b, n);
    }
#endif
  else
#if WANT_FFT || TUNE_PROGRAM_BUILD
    {
      mpn_mul_fft_full (p, a, n, b, n);
    }
#else
    {
      /* Toom8 for large operands. */
      mpn_toom8h_mul (p, a, n, b, n);
    }
#endif
}

void
mpn_sqr (mp_ptr p, mp_srcptr a, mp_size_t n)
{
  ASSERT (n >= 1);
  ASSERT (! MPN_OVERLAP_P (p, 2 * n, a, n));

#if 0
  /* FIXME: Can this be removed? */
  if (n == 0)
    return;
#endif

  if (BELOW_THRESHOLD (n, SQR_BASECASE_THRESHOLD))
    { /* mul_basecase is faster than sqr_basecase on small sizes sometimes */
      mpn_mul_basecase (p, a, n, a, n);
    }
  else if (BELOW_THRESHOLD (n, SQR_KARATSUBA_THRESHOLD))
    {
      mpn_sqr_basecase (p, a, n);
    }
  else if (BELOW_THRESHOLD (n, SQR_TOOM3_THRESHOLD))
    {
      /* Allocate workspace of fixed size on stack: fast! */
      mp_limb_t ws[MPN_KARA_SQR_N_TSIZE (SQR_TOOM3_THRESHOLD_LIMIT-1)];
      ASSERT (SQR_TOOM3_THRESHOLD <= SQR_TOOM3_THRESHOLD_LIMIT);
      mpn_kara_sqr_n (p, a, n, ws);
    }
  else if (BELOW_THRESHOLD (n, SQR_TOOM4_THRESHOLD))
    {
      mp_ptr ws;
      TMP_SDECL;
      TMP_SMARK;
      ws = TMP_SALLOC_LIMBS (MPN_TOOM3_SQR_N_TSIZE (n));
      mpn_toom3_sqr_n (p, a, n, ws);
      TMP_SFREE;
    }
  else if (BELOW_THRESHOLD (n, SQR_TOOM8_THRESHOLD))
    {
       mpn_toom4_sqr_n (p, a, n);
    }
#if WANT_FFT || TUNE_PROGRAM_BUILD
  else if (BELOW_THRESHOLD (n, SQR_FFT_FULL_THRESHOLD))
#else
  else 
#endif
    {
       mpn_toom8_sqr_n (p, a, n);
    }
#if WANT_FFT || TUNE_PROGRAM_BUILD
  else
    {
       mpn_mul_fft_full (p, a, n, a, n);
    }
#endif
}