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/* mpn_toom22_mul -- Multiply {ap,an} and {bp,bn} where an >= bn. Or more
accurately, bn <= an < 2bn.
Contributed to the GNU project by Torbjorn Granlund.
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 2006, 2007, 2008 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 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.
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 Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
#include "gmp.h"
#include "gmp-impl.h"
/* Evaluate in: -1, 0, +inf
<-s--><--n-->
____ ______
|_a1_|___a0_|
|b1_|___b0_|
<-t-><--n-->
v0 = a0 * b0 # A(0)*B(0)
vm1 = (a0- a1)*(b0- b1) # A(-1)*B(-1)
vinf= a1 * b1 # A(inf)*B(inf)
*/
#if TUNE_PROGRAM_BUILD
#define MAYBE_mul_toom22 1
#else
#define MAYBE_mul_toom22 \
(MUL_TOOM33_THRESHOLD >= 2 * MUL_TOOM22_THRESHOLD)
#endif
#define TOOM22_MUL_N_REC(p, a, b, n, ws) \
do { \
if (! MAYBE_mul_toom22 \
|| BELOW_THRESHOLD (n, MUL_KARATSUBA_THRESHOLD)) \
mpn_mul_basecase (p, a, n, b, n); \
else \
mpn_toom22_mul (p, a, n, b, n, ws); \
} while (0)
void
mpn_toom22_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;
int vm1_neg;
mp_limb_t cy, cy2;
mp_ptr asm1;
mp_ptr bsm1;
#define a0 ap
#define a1 (ap + n)
#define b0 bp
#define b1 (bp + n)
s = an >> 1;
n = an - s;
t = bn - n;
ASSERT (an >= bn);
ASSERT (0 < s && s <= n);
ASSERT (0 < t && t <= s);
asm1 = pp;
bsm1 = pp + n;
vm1_neg = 0;
/* Compute asm1. */
if (s == n)
{
if (mpn_cmp (a0, a1, n) < 0)
{
mpn_sub_n (asm1, a1, a0, n);
vm1_neg = 1;
}
else
{
mpn_sub_n (asm1, a0, a1, n);
}
}
else
{
if (mpn_zero_p (a0 + s, n - s) && mpn_cmp (a0, a1, s) < 0)
{
mpn_sub_n (asm1, a1, a0, s);
MPN_ZERO (asm1 + s, n - s);
vm1_neg = 1;
}
else
{
mpn_sub (asm1, a0, n, a1, s);
}
}
/* Compute bsm1. */
if (t == n)
{
if (mpn_cmp (b0, b1, n) < 0)
{
mpn_sub_n (bsm1, b1, b0, n);
vm1_neg ^= 1;
}
else
{
mpn_sub_n (bsm1, b0, b1, n);
}
}
else
{
if (mpn_zero_p (b0 + t, n - t) && mpn_cmp (b0, b1, t) < 0)
{
mpn_sub_n (bsm1, b1, b0, t);
MPN_ZERO (bsm1 + t, n - t);
vm1_neg ^= 1;
}
else
{
mpn_sub (bsm1, b0, n, b1, t);
}
}
#define v0 pp /* 2n */
#define vinf (pp + 2 * n) /* s+t */
#define vm1 scratch /* 2n */
#define scratch_out scratch + 2 * n
/* vm1, 2n limbs */
TOOM22_MUL_N_REC (vm1, asm1, bsm1, n, scratch_out);
/* vinf, s+t limbs */
mpn_mul (vinf, a1, s, b1, t);
/* v0, 2n limbs */
TOOM22_MUL_N_REC (v0, ap, bp, n, scratch_out);
/* H(v0) + L(vinf) */
cy = mpn_add_n (pp + 2 * n, v0 + n, vinf, n);
/* L(v0) + H(v0) */
cy2 = cy + mpn_add_n (pp + n, pp + 2 * n, v0, n);
/* L(vinf) + H(vinf) */
cy += mpn_add (pp + 2 * n, pp + 2 * n, n, vinf + n, s + t - n);
if (vm1_neg)
cy += mpn_add_n (pp + n, pp + n, vm1, 2 * n);
else
cy -= mpn_sub_n (pp + n, pp + n, vm1, 2 * n);
ASSERT (cy + 1 <= 3);
ASSERT (cy2 <= 2);
mpn_incr_u (pp + 2 * n, cy2);
if (LIKELY (cy <= 2))
mpn_incr_u (pp + 3 * n, cy);
else
mpn_decr_u (pp + 3 * n, 1);
}
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