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/* mpn_sub_err3_n -- sub_n with three error terms
Contributed by David Harvey.
THE FUNCTION IN THIS FILE IS INTERNAL WITH A MUTABLE INTERFACE. IT IS ONLY
SAFE TO REACH IT THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS ALMOST
GUARANTEED THAT IT'LL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
Copyright 2011 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 https://www.gnu.org/licenses/. */
#include "gmp.h"
#include "gmp-impl.h"
/*
Computes:
(1) {rp,n} := {up,n} - {vp,n} (just like mpn_sub_n) with incoming borrow cy,
return value is borrow out.
(2) Let c[i+1] = borrow from i-th limb subtraction (c[0] = cy).
Computes c[1]*yp1[n-1] + ... + c[n]*yp1[0],
c[1]*yp2[n-1] + ... + c[n]*yp2[0],
c[1]*yp3[n-1] + ... + c[n]*yp3[0],
stores two-limb results at {ep,2}, {ep+2,2} and {ep+4,2} respectively.
Requires n >= 1.
None of the outputs may overlap each other or any of the inputs, except
that {rp,n} may be equal to {up,n} or {vp,n}.
*/
mp_limb_t
mpn_sub_err3_n (mp_ptr rp, mp_srcptr up, mp_srcptr vp,
mp_ptr ep, mp_srcptr yp1, mp_srcptr yp2, mp_srcptr yp3,
mp_size_t n, mp_limb_t cy)
{
mp_limb_t el1, eh1, el2, eh2, el3, eh3, ul, vl, yl1, yl2, yl3, zl1, zl2, zl3, rl, sl, cy1, cy2;
ASSERT (n >= 1);
ASSERT (MPN_SAME_OR_SEPARATE_P (rp, up, n));
ASSERT (MPN_SAME_OR_SEPARATE_P (rp, vp, n));
ASSERT (! MPN_OVERLAP_P (rp, n, yp1, n));
ASSERT (! MPN_OVERLAP_P (rp, n, yp2, n));
ASSERT (! MPN_OVERLAP_P (rp, n, yp3, n));
ASSERT (! MPN_OVERLAP_P (ep, 6, up, n));
ASSERT (! MPN_OVERLAP_P (ep, 6, vp, n));
ASSERT (! MPN_OVERLAP_P (ep, 6, yp1, n));
ASSERT (! MPN_OVERLAP_P (ep, 6, yp2, n));
ASSERT (! MPN_OVERLAP_P (ep, 6, yp3, n));
ASSERT (! MPN_OVERLAP_P (ep, 6, rp, n));
yp1 += n - 1;
yp2 += n - 1;
yp3 += n - 1;
el1 = eh1 = 0;
el2 = eh2 = 0;
el3 = eh3 = 0;
do
{
yl1 = *yp1--;
yl2 = *yp2--;
yl3 = *yp3--;
ul = *up++;
vl = *vp++;
/* ordinary sub_n */
SUBC_LIMB (cy1, sl, ul, vl);
SUBC_LIMB (cy2, rl, sl, cy);
cy = cy1 | cy2;
*rp++ = rl;
/* update (eh1:el1) */
zl1 = (-cy) & yl1;
el1 += zl1;
eh1 += el1 < zl1;
/* update (eh2:el2) */
zl2 = (-cy) & yl2;
el2 += zl2;
eh2 += el2 < zl2;
/* update (eh3:el3) */
zl3 = (-cy) & yl3;
el3 += zl3;
eh3 += el3 < zl3;
}
while (--n);
#if GMP_NAIL_BITS != 0
eh1 = (eh1 << GMP_NAIL_BITS) + (el1 >> GMP_NUMB_BITS);
el1 &= GMP_NUMB_MASK;
eh2 = (eh2 << GMP_NAIL_BITS) + (el2 >> GMP_NUMB_BITS);
el2 &= GMP_NUMB_MASK;
eh3 = (eh3 << GMP_NAIL_BITS) + (el3 >> GMP_NUMB_BITS);
el3 &= GMP_NUMB_MASK;
#endif
ep[0] = el1;
ep[1] = eh1;
ep[2] = el2;
ep[3] = eh2;
ep[4] = el3;
ep[5] = eh3;
return cy;
}
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