1/* mpn_toom_eval_pm2rexp -- Evaluate a polynomial in +2^-k and -2^-k
2
3   Contributed to the GNU project by Marco Bodrato
4
5   THE FUNCTION IN THIS FILE IS INTERNAL WITH A MUTABLE INTERFACE.  IT IS ONLY
6   SAFE TO REACH IT THROUGH DOCUMENTED INTERFACES.  IN FACT, IT IS ALMOST
7   GUARANTEED THAT IT WILL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
8
9Copyright 2009 Free Software Foundation, Inc.
10
11This file is part of the GNU MP Library.
12
13The GNU MP Library is free software; you can redistribute it and/or modify
14it under the terms of the GNU Lesser General Public License as published by
15the Free Software Foundation; either version 3 of the License, or (at your
16option) any later version.
17
18The GNU MP Library is distributed in the hope that it will be useful, but
19WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
20or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
21License for more details.
22
23You should have received a copy of the GNU Lesser General Public License
24along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
25
26
27#include "gmp.h"
28#include "gmp-impl.h"
29
30#if HAVE_NATIVE_mpn_addlsh_n
31#define DO_mpn_addlsh_n(dst,src,n,s,ws) mpn_addlsh_n(dst,dst,src,n,s)
32#else
33static mp_limb_t
34DO_mpn_addlsh_n(mp_ptr dst, mp_srcptr src, mp_size_t n, unsigned int s, mp_ptr ws)
35{
36#if USE_MUL_1 && 0
37  return mpn_addmul_1(dst,src,n,CNST_LIMB(1) <<(s));
38#else
39  mp_limb_t __cy;
40  __cy = mpn_lshift(ws,src,n,s);
41  return    __cy + mpn_add_n(dst,dst,ws,n);
42#endif
43}
44#endif
45
46/* Evaluates a polynomial of degree k >= 3. */
47int
48mpn_toom_eval_pm2rexp (mp_ptr rp, mp_ptr rm,
49		      unsigned int q, mp_srcptr ap, mp_size_t n, mp_size_t t,
50		      unsigned int s, mp_ptr ws)
51{
52  unsigned int i;
53  int neg;
54  /* {ap,q*n+t} -> {rp,n+1} {rm,n+1} , with {ws, n+1}*/
55  ASSERT (n >= t);
56  ASSERT (s != 0); /* or _eval_pm1 should be used */
57  ASSERT (q > 1);
58  ASSERT (s*q < GMP_NUMB_BITS);
59  rp[n] = mpn_lshift(rp, ap, n, s*q);
60  ws[n] = mpn_lshift(ws, ap+n, n, s*(q-1));
61  if( (q & 1) != 0) {
62    ASSERT_NOCARRY(mpn_add(ws,ws,n+1,ap+n*q,t));
63    rp[n] += DO_mpn_addlsh_n(rp, ap+n*(q-1), n, s, rm);
64  } else {
65    ASSERT_NOCARRY(mpn_add(rp,rp,n+1,ap+n*q,t));
66  }
67  for(i=2; i<q-1; i++)
68  {
69    rp[n] += DO_mpn_addlsh_n(rp, ap+n*i, n, s*(q-i), rm);
70    i++;
71    ws[n] += DO_mpn_addlsh_n(ws, ap+n*i, n, s*(q-i), rm);
72  };
73
74  neg = (mpn_cmp (rp, ws, n + 1) < 0) ? ~0 : 0;
75
76#if HAVE_NATIVE_mpn_add_n_sub_n
77  if (neg)
78    mpn_add_n_sub_n (rp, rm, ws, rp, n + 1);
79  else
80    mpn_add_n_sub_n (rp, rm, rp, ws, n + 1);
81#else /* !HAVE_NATIVE_mpn_add_n_sub_n */
82  if (neg)
83    mpn_sub_n (rm, ws, rp, n + 1);
84  else
85    mpn_sub_n (rm, rp, ws, n + 1);
86
87  ASSERT_NOCARRY (mpn_add_n (rp, rp, ws, n + 1));
88#endif /* !HAVE_NATIVE_mpn_add_n_sub_n */
89
90  return neg;
91}
92