1/* mpn_toom2_sqr -- Square {ap,an}.
2
3   Contributed to the GNU project by Torbjorn Granlund.
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 2006, 2007, 2008, 2009, 2010 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/* Evaluate in: -1, 0, +inf
31
32  <-s--><--n-->
33   ____ ______
34  |_a1_|___a0_|
35
36  v0  =  a0     ^2  #   A(0)^2
37  vm1 = (a0- a1)^2  #  A(-1)^2
38  vinf=      a1 ^2  # A(inf)^2
39*/
40
41#if TUNE_PROGRAM_BUILD
42#define MAYBE_sqr_toom2   1
43#else
44#define MAYBE_sqr_toom2							\
45  (SQR_TOOM3_THRESHOLD >= 2 * SQR_TOOM2_THRESHOLD)
46#endif
47
48#define TOOM2_SQR_REC(p, a, n, ws)					\
49  do {									\
50    if (! MAYBE_sqr_toom2						\
51	|| BELOW_THRESHOLD (n, SQR_TOOM2_THRESHOLD))			\
52      mpn_sqr_basecase (p, a, n);					\
53    else								\
54      mpn_toom2_sqr (p, a, n, ws);					\
55  } while (0)
56
57void
58mpn_toom2_sqr (mp_ptr pp,
59	       mp_srcptr ap, mp_size_t an,
60	       mp_ptr scratch)
61{
62  mp_size_t n, s;
63  mp_limb_t cy, cy2;
64  mp_ptr asm1;
65
66#define a0  ap
67#define a1  (ap + n)
68
69  s = an >> 1;
70  n = an - s;
71
72  ASSERT (0 < s && s <= n);
73
74  asm1 = pp;
75
76  /* Compute asm1.  */
77  if (s == n)
78    {
79      if (mpn_cmp (a0, a1, n) < 0)
80	{
81	  mpn_sub_n (asm1, a1, a0, n);
82	}
83      else
84	{
85	  mpn_sub_n (asm1, a0, a1, n);
86	}
87    }
88  else
89    {
90      if (mpn_zero_p (a0 + s, n - s) && mpn_cmp (a0, a1, s) < 0)
91	{
92	  mpn_sub_n (asm1, a1, a0, s);
93	  MPN_ZERO (asm1 + s, n - s);
94	}
95      else
96	{
97	  mpn_sub (asm1, a0, n, a1, s);
98	}
99    }
100
101#define v0	pp				/* 2n */
102#define vinf	(pp + 2 * n)			/* s+s */
103#define vm1	scratch				/* 2n */
104#define scratch_out	scratch + 2 * n
105
106  /* vm1, 2n limbs */
107  TOOM2_SQR_REC (vm1, asm1, n, scratch_out);
108
109  /* vinf, s+s limbs */
110  TOOM2_SQR_REC (vinf, a1, s, scratch_out);
111
112  /* v0, 2n limbs */
113  TOOM2_SQR_REC (v0, ap, n, scratch_out);
114
115  /* H(v0) + L(vinf) */
116  cy = mpn_add_n (pp + 2 * n, v0 + n, vinf, n);
117
118  /* L(v0) + H(v0) */
119  cy2 = cy + mpn_add_n (pp + n, pp + 2 * n, v0, n);
120
121  /* L(vinf) + H(vinf) */
122  cy += mpn_add (pp + 2 * n, pp + 2 * n, n, vinf + n, s + s - n);
123
124  cy -= mpn_sub_n (pp + n, pp + n, vm1, 2 * n);
125
126  ASSERT (cy + 1  <= 3);
127  ASSERT (cy2 <= 2);
128
129  mpn_incr_u (pp + 2 * n, cy2);
130  if (LIKELY (cy <= 2))
131    mpn_incr_u (pp + 3 * n, cy);
132  else
133    mpn_decr_u (pp + 3 * n, 1);
134}
135