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/* mpfr_eq -- Compare two floats up to a specified bit #.
Copyright 1999, 2001, 2003-2004, 2006-2020 Free Software Foundation, Inc.
Contributed by the AriC and Caramba projects, INRIA.
This file is part of the GNU MPFR Library.
The GNU MPFR 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 MPFR 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 MPFR Library; see the file COPYING.LESSER. If not, see
https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
#include "mpfr-impl.h"
/* return non-zero if the first n_bits bits of u, v are equal,
0 otherwise */
int
mpfr_eq (mpfr_srcptr u, mpfr_srcptr v, unsigned long int n_bits)
{
mpfr_limb_srcptr up, vp;
mp_size_t usize, vsize, size, i;
mpfr_exp_t uexp, vexp;
int k;
if (MPFR_ARE_SINGULAR(u, v))
{
if (MPFR_IS_NAN(u) || MPFR_IS_NAN(v))
return 0; /* non equal */
else if (MPFR_IS_INF(u) && MPFR_IS_INF(v))
return (MPFR_SIGN(u) == MPFR_SIGN(v));
else if (MPFR_IS_ZERO(u) && MPFR_IS_ZERO(v))
return 1;
else
return 0;
}
/* 1. Are the signs different? */
if (MPFR_SIGN(u) != MPFR_SIGN(v))
return 0;
uexp = MPFR_GET_EXP (u);
vexp = MPFR_GET_EXP (v);
/* 2. Are the exponents different? */
if (uexp != vexp)
return 0; /* no bit agree */
usize = MPFR_LIMB_SIZE (u);
vsize = MPFR_LIMB_SIZE (v);
if (vsize > usize) /* exchange u and v */
{
up = MPFR_MANT(v);
vp = MPFR_MANT(u);
size = vsize;
vsize = usize;
usize = size;
}
else
{
up = MPFR_MANT(u);
vp = MPFR_MANT(v);
}
/* now usize >= vsize */
MPFR_ASSERTD(usize >= vsize);
if (usize > vsize)
{
if ((unsigned long) vsize * GMP_NUMB_BITS < n_bits)
{
/* check if low min(PREC(u), n_bits) - (vsize * GMP_NUMB_BITS)
bits from u are non-zero */
unsigned long remains = n_bits - (vsize * GMP_NUMB_BITS);
k = usize - vsize - 1;
while (k >= 0 && remains >= GMP_NUMB_BITS && !up[k])
{
k--;
remains -= GMP_NUMB_BITS;
}
/* now either k < 0: all low bits from u are zero
or remains < GMP_NUMB_BITS: check high bits from up[k]
or up[k] <> 0: different */
if (k >= 0 && (((remains < GMP_NUMB_BITS) &&
(up[k] >> (GMP_NUMB_BITS - remains))) ||
(remains >= GMP_NUMB_BITS && up[k])))
return 0; /* surely too different */
}
size = vsize;
}
else
{
size = usize;
}
/* now size = min (usize, vsize) */
/* If size is too large wrt n_bits, reduce it to look only at the
high n_bits bits.
Otherwise, if n_bits > size * GMP_NUMB_BITS, reduce n_bits to
size * GMP_NUMB_BITS, since the extra low bits of one of the
operands have already been check above. */
if ((unsigned long) size > 1 + (n_bits - 1) / GMP_NUMB_BITS)
size = 1 + (n_bits - 1) / GMP_NUMB_BITS;
else if (n_bits > (unsigned long) size * GMP_NUMB_BITS)
n_bits = size * GMP_NUMB_BITS;
up += usize - size;
vp += vsize - size;
for (i = size - 1; i > 0 && n_bits >= GMP_NUMB_BITS; i--)
{
if (up[i] != vp[i])
return 0;
n_bits -= GMP_NUMB_BITS;
}
/* now either i=0 or n_bits<GMP_NUMB_BITS */
/* since n_bits <= size * GMP_NUMB_BITS before the above for-loop,
we have the invariant n_bits <= (i+1) * GMP_NUMB_BITS, thus
we always have n_bits <= GMP_NUMB_BITS here */
MPFR_ASSERTD(n_bits <= GMP_NUMB_BITS);
if (n_bits & (GMP_NUMB_BITS - 1))
return (up[i] >> (GMP_NUMB_BITS - (n_bits & (GMP_NUMB_BITS - 1))) ==
vp[i] >> (GMP_NUMB_BITS - (n_bits & (GMP_NUMB_BITS - 1))));
else
return (up[i] == vp[i]);
}
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