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/* Cray PVP/IEEE mpn_submul_1 -- multiply a limb vector with a limb and
subtract the result from a second limb vector.
Copyright 2000-2002 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 https://www.gnu.org/licenses/. */
/* This code runs at just under 9 cycles/limb on a T90. That is not perfect,
mainly due to vector register shortage in the main loop. Assembly code
should bring it down to perhaps 7 cycles/limb. */
#include <intrinsics.h>
#include "gmp.h"
#include "gmp-impl.h"
mp_limb_t
mpn_submul_1 (mp_ptr rp, mp_srcptr up, mp_size_t n, mp_limb_t vl)
{
mp_limb_t cy[n];
mp_limb_t a, b, r, s0, s1, c0, c1;
mp_size_t i;
int more_carries;
if (up == rp)
{
/* The algorithm used below cannot handle overlap. Handle it here by
making a temporary copy of the source vector, then call ourselves. */
mp_limb_t xp[n];
MPN_COPY (xp, up, n);
return mpn_submul_1 (rp, xp, n, vl);
}
a = up[0] * vl;
r = rp[0];
s0 = r - a;
rp[0] = s0;
c1 = ((s0 & a) | ((s0 | a) & ~r)) >> 63;
cy[0] = c1;
/* Main multiply loop. Generate a raw accumulated output product in rp[]
and a carry vector in cy[]. */
#pragma _CRI ivdep
for (i = 1; i < n; i++)
{
a = up[i] * vl;
b = _int_mult_upper (up[i - 1], vl);
s0 = a + b;
c0 = ((a & b) | ((a | b) & ~s0)) >> 63;
r = rp[i];
s1 = r - s0;
rp[i] = s1;
c1 = ((s1 & s0) | ((s1 | s0) & ~r)) >> 63;
cy[i] = c0 + c1;
}
/* Carry subtract loop. Subtract the carry vector cy[] from the raw result
rp[] and store the new result back to rp[]. */
more_carries = 0;
#pragma _CRI ivdep
for (i = 1; i < n; i++)
{
r = rp[i];
c0 = cy[i - 1];
s0 = r - c0;
rp[i] = s0;
c0 = (s0 & ~r) >> 63;
more_carries += c0;
}
/* If that second loop generated carry, handle that in scalar loop. */
if (more_carries)
{
mp_limb_t cyrec = 0;
/* Look for places where rp[k] == ~0 and cy[k-1] == 1 or
rp[k] == ~1 and cy[k-1] == 2.
These are where we got a recurrency carry. */
for (i = 1; i < n; i++)
{
r = rp[i];
c0 = ~r < cy[i - 1];
s0 = r - cyrec;
rp[i] = s0;
c1 = (s0 & ~r) >> 63;
cyrec = c0 | c1;
}
return _int_mult_upper (up[n - 1], vl) + cyrec + cy[n - 1];
}
return _int_mult_upper (up[n - 1], vl) + cy[n - 1];
}
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