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/* mpn_toom43_mul -- Multiply {ap,an} and {bp,bn} where an is nominally 4/3
times as large as bn. Or more accurately, bn < an < 2 bn.
Contributed to the GNU project by Marco Bodrato.
The idea of applying toom to unbalanced multiplication is due to Marco
Bodrato and Alberto Zanoni.
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 WILL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
Copyright 2009, 2020 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 either:
* 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.
or
* the GNU General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any
later version.
or both in parallel, as here.
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 General Public License
for more details.
You should have received copies of the GNU General Public License and the
GNU Lesser General Public License along with the GNU MP Library. If not,
see https://www.gnu.org/licenses/. */
#include "gmp-impl.h"
/* Evaluate in: -2, -1, 0, +1, +2, +inf
<-s-><--n--><--n--><--n-->
___ ______ ______ ______
|a3_|___a2_|___a1_|___a0_|
|_b2_|___b1_|___b0_|
<-t--><--n--><--n-->
v0 = a0 * b0 # A(0)*B(0)
v1 = (a0+ a1+ a2+ a3)*(b0+ b1+ b2) # A(1)*B(1) ah <= 3 bh <= 2
vm1 = (a0- a1+ a2- a3)*(b0- b1+ b2) # A(-1)*B(-1) |ah| <= 1 |bh|<= 1
v2 = (a0+2a1+4a2+8a3)*(b0+2b1+4b2) # A(2)*B(2) ah <= 14 bh <= 6
vm2 = (a0-2a1+4a2-8a3)*(b0-2b1+4b2) # A(-2)*B(-2) |ah| <= 9 |bh|<= 4
vinf= a3 * b2 # A(inf)*B(inf)
*/
void
mpn_toom43_mul (mp_ptr pp,
mp_srcptr ap, mp_size_t an,
mp_srcptr bp, mp_size_t bn, mp_ptr scratch)
{
mp_size_t n, s, t;
enum toom6_flags flags;
mp_limb_t cy;
#define a0 ap
#define a1 (ap + n)
#define a2 (ap + 2 * n)
#define a3 (ap + 3 * n)
#define b0 bp
#define b1 (bp + n)
#define b2 (bp + 2 * n)
n = 1 + (3 * an >= 4 * bn ? (an - 1) >> 2 : (bn - 1) / (size_t) 3);
s = an - 3 * n;
t = bn - 2 * n;
ASSERT (0 < s && s <= n);
ASSERT (0 < t && t <= n);
/* This is true whenever an >= 25 or bn >= 19, I think. It
guarantees that we can fit 5 values of size n+1 in the product
area. */
ASSERT (s+t >= 5);
#define v0 pp /* 2n */
#define vm1 (scratch) /* 2n+1 */
#define v1 (pp + 2*n) /* 2n+1 */
#define vm2 (scratch + 2 * n + 1) /* 2n+1 */
#define v2 (scratch + 4 * n + 2) /* 2n+1 */
#define vinf (pp + 5 * n) /* s+t */
#define bs1 pp /* n+1 */
#define bsm1 (scratch + 2 * n + 2) /* n+1 */
#define asm1 (scratch + 3 * n + 3) /* n+1 */
#define asm2 (scratch + 4 * n + 4) /* n+1 */
#define bsm2 (pp + n + 1) /* n+1 */
#define bs2 (pp + 2 * n + 2) /* n+1 */
#define as2 (pp + 3 * n + 3) /* n+1 */
#define as1 (pp + 4 * n + 4) /* n+1 */
/* Total sccratch need is 6 * n + 3 + 1; we allocate one extra
limb, because products will overwrite 2n+2 limbs. */
#define a0a2 scratch
#define b0b2 scratch
#define a1a3 asm1
#define b1d bsm1
/* Compute as2 and asm2. */
flags = (enum toom6_flags) (toom6_vm2_neg & mpn_toom_eval_dgr3_pm2 (as2, asm2, ap, n, s, a1a3));
/* Compute bs2 and bsm2. */
b1d[n] = mpn_lshift (b1d, b1, n, 1); /* 2b1 */
#if HAVE_NATIVE_mpn_addlsh2_n
cy = mpn_addlsh2_n (b0b2, b0, b2, t); /* 4b2 + b0 */
#else
cy = mpn_lshift (b0b2, b2, t, 2); /* 4b2 */
cy += mpn_add_n (b0b2, b0b2, b0, t); /* 4b2 + b0 */
#endif
if (t != n)
cy = mpn_add_1 (b0b2 + t, b0 + t, n - t, cy);
b0b2[n] = cy;
#if HAVE_NATIVE_mpn_add_n_sub_n
if (mpn_cmp (b0b2, b1d, n+1) < 0)
{
mpn_add_n_sub_n (bs2, bsm2, b1d, b0b2, n+1);
flags = (enum toom6_flags) (flags ^ toom6_vm2_neg);
}
else
{
mpn_add_n_sub_n (bs2, bsm2, b0b2, b1d, n+1);
}
#else
mpn_add_n (bs2, b0b2, b1d, n+1);
if (mpn_cmp (b0b2, b1d, n+1) < 0)
{
mpn_sub_n (bsm2, b1d, b0b2, n+1);
flags = (enum toom6_flags) (flags ^ toom6_vm2_neg);
}
else
{
mpn_sub_n (bsm2, b0b2, b1d, n+1);
}
#endif
/* Compute as1 and asm1. */
flags = (enum toom6_flags) (flags ^ (toom6_vm1_neg & mpn_toom_eval_dgr3_pm1 (as1, asm1, ap, n, s, a0a2)));
/* Compute bs1 and bsm1. */
bsm1[n] = mpn_add (bsm1, b0, n, b2, t);
#if HAVE_NATIVE_mpn_add_n_sub_n
if (bsm1[n] == 0 && mpn_cmp (bsm1, b1, n) < 0)
{
cy = mpn_add_n_sub_n (bs1, bsm1, b1, bsm1, n);
bs1[n] = cy >> 1;
flags = (enum toom6_flags) (flags ^ toom6_vm1_neg);
}
else
{
cy = mpn_add_n_sub_n (bs1, bsm1, bsm1, b1, n);
bs1[n] = bsm1[n] + (cy >> 1);
bsm1[n]-= cy & 1;
}
#else
bs1[n] = bsm1[n] + mpn_add_n (bs1, bsm1, b1, n);
if (bsm1[n] == 0 && mpn_cmp (bsm1, b1, n) < 0)
{
mpn_sub_n (bsm1, b1, bsm1, n);
flags = (enum toom6_flags) (flags ^ toom6_vm1_neg);
}
else
{
bsm1[n] -= mpn_sub_n (bsm1, bsm1, b1, n);
}
#endif
ASSERT (as1[n] <= 3);
ASSERT (bs1[n] <= 2);
ASSERT (asm1[n] <= 1);
ASSERT (bsm1[n] <= 1);
ASSERT (as2[n] <=14);
ASSERT (bs2[n] <= 6);
ASSERT (asm2[n] <= 9);
ASSERT (bsm2[n] <= 4);
/* vm1, 2n+1 limbs */
vm1[2*n] = 0;
mpn_mul_n (vm1, asm1, bsm1, n + (asm1[n] | bsm1[n])); /* W4 */
/* vm2, 2n+1 limbs */
mpn_mul_n (vm2, asm2, bsm2, n+1); /* W2 */
/* v2, 2n+1 limbs */
mpn_mul_n (v2, as2, bs2, n+1); /* W1 */
/* v1, 2n+1 limbs */
mpn_mul_n (v1, as1, bs1, n+1); /* W3 */
/* vinf, s+t limbs */ /* W0 */
if (s > t) mpn_mul (vinf, a3, s, b2, t);
else mpn_mul (vinf, b2, t, a3, s);
/* v0, 2n limbs */
mpn_mul_n (v0, ap, bp, n); /* W5 */
mpn_toom_interpolate_6pts (pp, n, flags, vm1, vm2, v2, t + s);
#undef v0
#undef vm1
#undef v1
#undef vm2
#undef v2
#undef vinf
#undef bs1
#undef bs2
#undef bsm1
#undef bsm2
#undef asm1
#undef asm2
/* #undef as1 */
/* #undef as2 */
#undef a0a2
#undef b0b2
#undef a1a3
#undef b1d
#undef a0
#undef a1
#undef a2
#undef a3
#undef b0
#undef b1
#undef b2
}
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