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
9 Copyright 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
10
11 This file is part of the GNU MP Library.
12
13 The GNU MP Library is free software; you can redistribute it and/or modify
14 it under the terms of the GNU Lesser General Public License as published by
15 the Free Software Foundation; either version 3 of the License, or (at your
16 option) any later version.
17
18 The GNU MP Library is distributed in the hope that it will be useful, but
19 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
20 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
21 License for more details.
22
23 You should have received a copy of the GNU Lesser General Public License
24 along 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
57 void
mpn_toom2_sqr(mp_ptr pp,mp_srcptr ap,mp_size_t an,mp_ptr scratch)58 mpn_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