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freebsd-dev/contrib/libgmp/mpf/sub.c
Mark Murray aa9bc17601 Clean import of libgmp 2.0.2, with only the non-x86 bits removed. 
BMakefiles and other bits will follow.

Requested by:	Andrey Chernov
Made world by:	Chuck Robey
1996-10-20 08:49:26 +00:00

403 lines
8.8 KiB
C
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/* mpf_sub -- Subtract two floats.
Copyright (C) 1993, 1994, 1995, 1996 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 Library General Public License as published by
the Free Software Foundation; either version 2 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 Library General Public
License for more details.
You should have received a copy of the GNU Library General Public License
along with the GNU MP Library; see the file COPYING.LIB. If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */
#include "gmp.h"
#include "gmp-impl.h"
void
#if __STDC__
mpf_sub (mpf_ptr r, mpf_srcptr u, mpf_srcptr v)
#else
mpf_sub (r, u, v)
mpf_ptr r;
mpf_srcptr u;
mpf_srcptr v;
#endif
{
mp_srcptr up, vp;
mp_ptr rp, tp;
mp_size_t usize, vsize, rsize;
mp_size_t prec;
mp_exp_t exp;
mp_size_t ediff;
int negate;
TMP_DECL (marker);
usize = u->_mp_size;
vsize = v->_mp_size;
/* Handle special cases that don't work in generic code below. */
if (usize == 0)
{
mpf_neg (r, v);
return;
}
if (vsize == 0)
{
mpf_set (r, u);
return;
}
/* If signs of U and V are different, perform addition. */
if ((usize ^ vsize) < 0)
{
__mpf_struct v_negated;
v_negated._mp_size = -vsize;
v_negated._mp_exp = v->_mp_exp;
v_negated._mp_d = v->_mp_d;
mpf_add (r, u, &v_negated);
return;
}
TMP_MARK (marker);
/* Signs are now known to be the same. */
negate = usize < 0;
/* Make U be the operand with the largest exponent. */
if (u->_mp_exp < v->_mp_exp)
{
mpf_srcptr t;
t = u; u = v; v = t;
negate ^= 1;
usize = u->_mp_size;
vsize = v->_mp_size;
}
usize = ABS (usize);
vsize = ABS (vsize);
up = u->_mp_d;
vp = v->_mp_d;
rp = r->_mp_d;
prec = r->_mp_prec + 1;
exp = u->_mp_exp;
ediff = u->_mp_exp - v->_mp_exp;
/* If ediff is 0 or 1, we might have a situation where the operands are
extremely close. We need to scan the operands from the most significant
end ignore the initial parts that are equal. */
if (ediff <= 1)
{
if (ediff == 0)
{
/* Skip leading limbs in U and V that are equal. */
if (up[usize - 1] == vp[vsize - 1])
{
/* This loop normally exits immediately. Optimize for that. */
do
{
usize--;
vsize--;
exp--;
if (usize == 0)
{
rsize = vsize;
tp = (mp_ptr) vp;
negate ^= 1;
goto normalize;
}
if (vsize == 0)
{
rsize = usize;
tp = (mp_ptr) up;
goto normalize;
}
}
while (up[usize - 1] == vp[vsize - 1]);
}
if (up[usize - 1] < vp[vsize - 1])
{
/* For simplicity, swap U and V. Note that since the loop above
wouldn't have exited unless up[usize - 1] and vp[vsize - 1]
were non-equal, this if-statement catches all cases where U
is smaller than V. */
{ mp_srcptr tp = up; up = vp; vp = tp; }
{ mp_size_t tsize = usize; usize = vsize; vsize = tsize; }
negate ^= 1;
/* negating ediff not necessary since it is 0. */
}
/* Check for
x+1 00000000 ...
x ffffffff ... */
if (up[usize - 1] != vp[vsize - 1] + 1)
goto general_case;
usize--;
vsize--;
exp--;
}
else /* ediff == 1 */
{
/* Check for
1 00000000 ...
0 ffffffff ... */
if (up[usize - 1] != 1 || vp[vsize - 1] != ~(mp_limb_t) 0
|| (usize >= 2 && up[usize - 2] != 0))
goto general_case;
usize--;
exp--;
}
/* Skip sequences of 00000000/ffffffff */
while (vsize != 0 && usize != 0 && up[usize - 1] == 0
&& vp[vsize - 1] == ~(mp_limb_t) 0)
{
usize--;
vsize--;
exp--;
}
if (usize == 0)
{
while (vsize != 0 && vp[vsize - 1] == ~(mp_limb_t) 0)
{
vsize--;
exp--;
}
}
if (usize > prec - 1)
{
up += usize - (prec - 1);
usize = prec - 1;
}
if (vsize > prec - 1)
{
vp += vsize - (prec - 1);
vsize = prec - 1;
}
tp = (mp_ptr) TMP_ALLOC (prec * BYTES_PER_MP_LIMB);
{
mp_limb_t cy_limb;
if (vsize == 0)
{
mp_size_t size, i;
size = usize;
for (i = 0; i < size; i++)
tp[i] = up[i];
tp[size] = 1;
rsize = size + 1;
exp++;
goto normalize;
}
if (usize == 0)
{
mp_size_t size, i;
size = vsize;
for (i = 0; i < size; i++)
tp[i] = ~vp[i];
cy_limb = 1 - mpn_add_1 (tp, tp, vsize, (mp_limb_t) 1);
rsize = vsize;
if (cy_limb == 0)
{
tp[rsize] = 1;
rsize++;
exp++;
}
goto normalize;
}
if (usize >= vsize)
{
/* uuuu */
/* vv */
mp_size_t size;
size = usize - vsize;
MPN_COPY (tp, up, size);
cy_limb = mpn_sub_n (tp + size, up + size, vp, vsize);
rsize = usize;
}
else /* (usize < vsize) */
{
/* uuuu */
/* vvvvvvv */
mp_size_t size, i;
size = vsize - usize;
for (i = 0; i < size; i++)
tp[i] = ~vp[i];
cy_limb = mpn_sub_n (tp + size, up, vp + size, usize);
cy_limb+= mpn_sub_1 (tp + size, tp + size, usize, (mp_limb_t) 1);
cy_limb-= mpn_add_1 (tp, tp, vsize, (mp_limb_t) 1);
rsize = vsize;
}
if (cy_limb == 0)
{
tp[rsize] = 1;
rsize++;
exp++;
}
goto normalize;
}
}
general_case:
/* If U extends beyond PREC, ignore the part that does. */
if (usize > prec)
{
up += usize - prec;
usize = prec;
}
/* If V extends beyond PREC, ignore the part that does.
Note that this may make vsize negative. */
if (vsize + ediff > prec)
{
vp += vsize + ediff - prec;
vsize = prec - ediff;
}
/* Allocate temp space for the result. Allocate
just vsize + ediff later??? */
tp = (mp_ptr) TMP_ALLOC (prec * BYTES_PER_MP_LIMB);
if (ediff >= prec)
{
/* V completely cancelled. */
if (tp != up)
MPN_COPY (rp, up, usize);
rsize = usize;
}
else
{
/* Locate the least significant non-zero limb in (the needed
parts of) U and V, to simplify the code below. */
for (;;)
{
if (vsize == 0)
{
MPN_COPY (rp, up, usize);
rsize = usize;
goto done;
}
if (vp[0] != 0)
break;
vp++, vsize--;
}
for (;;)
{
if (usize == 0)
{
MPN_COPY (rp, vp, vsize);
rsize = vsize;
negate ^= 1;
goto done;
}
if (up[0] != 0)
break;
up++, usize--;
}
/* uuuu | uuuu | uuuu | uuuu | uuuu */
/* vvvvvvv | vv | vvvvv | v | vv */
if (usize > ediff)
{
/* U and V partially overlaps. */
if (ediff == 0)
{
/* Have to compare the leading limbs of u and v
to determine whether to compute u - v or v - u. */
if (usize >= vsize)
{
/* uuuu */
/* vv */
mp_size_t size;
size = usize - vsize;
MPN_COPY (tp, up, size);
mpn_sub_n (tp + size, up + size, vp, vsize);
rsize = usize;
}
else /* (usize < vsize) */
{
/* uuuu */
/* vvvvvvv */
mp_size_t size, i;
size = vsize - usize;
tp[0] = -vp[0];
for (i = 1; i < size; i++)
tp[i] = ~vp[i];
mpn_sub_n (tp + size, up, vp + size, usize);
mpn_sub_1 (tp + size, tp + size, usize, (mp_limb_t) 1);
rsize = vsize;
}
}
else
{
if (vsize + ediff <= usize)
{
/* uuuu */
/* v */
mp_size_t size;
size = usize - ediff - vsize;
MPN_COPY (tp, up, size);
mpn_sub (tp + size, up + size, usize - size, vp, vsize);
rsize = usize;
}
else
{
/* uuuu */
/* vvvvv */
mp_size_t size, i;
size = vsize + ediff - usize;
tp[0] = -vp[0];
for (i = 1; i < size; i++)
tp[i] = ~vp[i];
mpn_sub (tp + size, up, usize, vp + size, usize - ediff);
mpn_sub_1 (tp + size, tp + size, usize, (mp_limb_t) 1);
rsize = vsize + ediff;
}
}
}
else
{
/* uuuu */
/* vv */
mp_size_t size, i;
size = vsize + ediff - usize;
tp[0] = -vp[0];
for (i = 1; i < vsize; i++)
tp[i] = ~vp[i];
for (i = vsize; i < size; i++)
tp[i] = ~(mp_limb_t) 0;
mpn_sub_1 (tp + size, up, usize, (mp_limb_t) 1);
rsize = size + usize;
}
normalize:
/* Full normalize. Optimize later. */
while (rsize != 0 && tp[rsize - 1] == 0)
{
rsize--;
exp--;
}
MPN_COPY (rp, tp, rsize);
}
done:
r->_mp_size = negate ? -rsize : rsize;
r->_mp_exp = exp;
TMP_FREE (marker);
}
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