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 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 |b1_|___b0_| 36 <-t-><--n--> 37 38 v0 = a0 * b0 # A(0)*B(0) 39 vm1 = (a0- a1)*(b0- b1) # A(-1)*B(-1) 40 vinf= a1 * b1 # A(inf)*B(inf) 41 */ 42 43 #if TUNE_PROGRAM_BUILD 44 #define MAYBE_sqr_toom2 1 45 #else 46 #define MAYBE_sqr_toom2 \ 47 (SQR_TOOM3_THRESHOLD >= 2 * SQR_TOOM2_THRESHOLD) 48 #endif 49 50 #define TOOM2_SQR_N_REC(p, a, n, ws) \ 51 do { \ 52 if (! MAYBE_sqr_toom2 \ 53 || BELOW_THRESHOLD (n, SQR_KARATSUBA_THRESHOLD)) \ 54 mpn_sqr_basecase (p, a, n); \ 55 else \ 56 mpn_toom2_sqr (p, a, n, ws); \ 57 } while (0) 58 59 void 60 mpn_toom2_sqr (mp_ptr pp, 61 mp_srcptr ap, mp_size_t an, 62 mp_ptr scratch) 63 { 64 mp_size_t n, s; 65 mp_limb_t cy, cy2; 66 mp_ptr asm1; 67 68 #define a0 ap 69 #define a1 (ap + n) 70 71 s = an >> 1; 72 n = an - s; 73 74 ASSERT (0 < s && s <= n); 75 76 asm1 = pp; 77 78 /* Compute asm1. */ 79 if (s == n) 80 { 81 if (mpn_cmp (a0, a1, n) < 0) 82 { 83 mpn_sub_n (asm1, a1, a0, n); 84 } 85 else 86 { 87 mpn_sub_n (asm1, a0, a1, n); 88 } 89 } 90 else 91 { 92 if (mpn_zero_p (a0 + s, n - s) && mpn_cmp (a0, a1, s) < 0) 93 { 94 mpn_sub_n (asm1, a1, a0, s); 95 MPN_ZERO (asm1 + s, n - s); 96 } 97 else 98 { 99 mpn_sub (asm1, a0, n, a1, s); 100 } 101 } 102 103 #define v0 pp /* 2n */ 104 #define vinf (pp + 2 * n) /* s+s */ 105 #define vm1 scratch /* 2n */ 106 107 /* vm1, 2n limbs */ 108 TOOM2_SQR_N_REC (vm1, asm1, n, scratch); 109 110 /* vinf, s+s limbs */ 111 TOOM2_SQR_N_REC (vinf, a1, s, scratch); 112 113 /* v0, 2n limbs */ 114 TOOM2_SQR_N_REC (v0, ap, n, scratch); 115 116 /* H(v0) + L(vinf) */ 117 cy = mpn_add_n (pp + 2 * n, v0 + n, vinf, n); 118 119 /* L(v0) + H(v0) */ 120 cy2 = cy + mpn_add_n (pp + n, pp + 2 * n, v0, n); 121 122 /* L(vinf) + H(vinf) */ 123 cy += mpn_add (pp + 2 * n, pp + 2 * n, n, vinf + n, s + s - n); 124 125 cy -= mpn_sub_n (pp + n, pp + n, vm1, 2 * n); 126 127 ASSERT (cy + 1 <= 3); 128 ASSERT (cy2 <= 2); 129 130 mpn_incr_u (pp + 2 * n, cy2); 131 if (LIKELY (cy <= 2)) 132 mpn_incr_u (pp + 3 * n, cy); 133 else 134 mpn_decr_u (pp + 3 * n, 1); 135 } 136