1  /* mpn_submul_1 -- multiply the N long limb vector pointed to by UP by VL,
       2     subtract the N least significant limbs of the product from the limb
       3     vector pointed to by RP.  Return the most significant limb of the
       4     product, adjusted for carry-out from the subtraction.
       5  
       6  Copyright 1992-1994, 1996, 2000, 2002, 2004 Free Software Foundation, Inc.
       7  
       8  This file is part of the GNU MP Library.
       9  
      10  The GNU MP Library is free software; you can redistribute it and/or modify
      11  it under the terms of either:
      12  
      13    * the GNU Lesser General Public License as published by the Free
      14      Software Foundation; either version 3 of the License, or (at your
      15      option) any later version.
      16  
      17  or
      18  
      19    * the GNU General Public License as published by the Free Software
      20      Foundation; either version 2 of the License, or (at your option) any
      21      later version.
      22  
      23  or both in parallel, as here.
      24  
      25  The GNU MP Library is distributed in the hope that it will be useful, but
      26  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
      27  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
      28  for more details.
      29  
      30  You should have received copies of the GNU General Public License and the
      31  GNU Lesser General Public License along with the GNU MP Library.  If not,
      32  see https://www.gnu.org/licenses/.  */
      33  
      34  #include "gmp-impl.h"
      35  #include "longlong.h"
      36  
      37  
      38  #if GMP_NAIL_BITS == 0
      39  
      40  mp_limb_t
      41  mpn_submul_1 (mp_ptr rp, mp_srcptr up, mp_size_t n, mp_limb_t v0)
      42  {
      43    mp_limb_t u0, crec, c, p1, p0, r0;
      44  
      45    ASSERT (n >= 1);
      46    ASSERT (MPN_SAME_OR_SEPARATE_P (rp, up, n));
      47  
      48    crec = 0;
      49    do
      50      {
      51        u0 = *up++;
      52        umul_ppmm (p1, p0, u0, v0);
      53  
      54        r0 = *rp;
      55  
      56        p0 = r0 - p0;
      57        c = r0 < p0;
      58  
      59        p1 = p1 + c;
      60  
      61        r0 = p0 - crec;		/* cycle 0, 3, ... */
      62        c = p0 < r0;		/* cycle 1, 4, ... */
      63  
      64        crec = p1 + c;		/* cycle 2, 5, ... */
      65  
      66        *rp++ = r0;
      67      }
      68    while (--n != 0);
      69  
      70    return crec;
      71  }
      72  
      73  #endif
      74  
      75  #if GMP_NAIL_BITS == 1
      76  
      77  mp_limb_t
      78  mpn_submul_1 (mp_ptr rp, mp_srcptr up, mp_size_t n, mp_limb_t v0)
      79  {
      80    mp_limb_t shifted_v0, u0, r0, p0, p1, prev_p1, cl, xl, c1, c2, c3;
      81  
      82    ASSERT (n >= 1);
      83    ASSERT (MPN_SAME_OR_SEPARATE_P (rp, up, n));
      84    ASSERT_MPN (rp, n);
      85    ASSERT_MPN (up, n);
      86    ASSERT_LIMB (v0);
      87  
      88    shifted_v0 = v0 << GMP_NAIL_BITS;
      89    cl = 0;
      90    prev_p1 = 0;
      91    do
      92      {
      93        u0 = *up++;
      94        r0 = *rp;
      95        umul_ppmm (p1, p0, u0, shifted_v0);
      96        p0 >>= GMP_NAIL_BITS;
      97        SUBC_LIMB (c1, xl, r0, prev_p1);
      98        SUBC_LIMB (c2, xl, xl, p0);
      99        SUBC_LIMB (c3, xl, xl, cl);
     100        cl = c1 + c2 + c3;
     101        *rp++ = xl;
     102        prev_p1 = p1;
     103      }
     104    while (--n != 0);
     105  
     106    return prev_p1 + cl;
     107  }
     108  
     109  #endif
     110  
     111  #if GMP_NAIL_BITS >= 2
     112  
     113  mp_limb_t
     114  mpn_submul_1 (mp_ptr rp, mp_srcptr up, mp_size_t n, mp_limb_t v0)
     115  {
     116    mp_limb_t shifted_v0, u0, r0, p0, p1, prev_p1, xw, cl, xl;
     117  
     118    ASSERT (n >= 1);
     119    ASSERT (MPN_SAME_OR_SEPARATE_P (rp, up, n));
     120    ASSERT_MPN (rp, n);
     121    ASSERT_MPN (up, n);
     122    ASSERT_LIMB (v0);
     123  
     124    shifted_v0 = v0 << GMP_NAIL_BITS;
     125    cl = 0;
     126    prev_p1 = 0;
     127    do
     128      {
     129        u0 = *up++;
     130        r0 = *rp;
     131        umul_ppmm (p1, p0, u0, shifted_v0);
     132        p0 >>= GMP_NAIL_BITS;
     133        xw = r0 - (prev_p1 + p0) + cl;
     134        cl = (mp_limb_signed_t) xw >> GMP_NUMB_BITS; /* FIXME: non-portable */
     135        xl = xw & GMP_NUMB_MASK;
     136        *rp++ = xl;
     137        prev_p1 = p1;
     138      }
     139    while (--n != 0);
     140  
     141    return prev_p1 - cl;
     142  }
     143  
     144  #endif