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/* mpz_hamdist -- calculate hamming distance.
Copyright 1994, 1996, 2001, 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 http://www.gnu.org/licenses/. */
#include "gmp.h"
#include "gmp-impl.h"
unsigned long
mpz_hamdist (mpz_srcptr u, mpz_srcptr v)
{
mp_srcptr up, vp;
mp_size_t usize, vsize;
unsigned long count;
usize = SIZ(u);
vsize = SIZ(v);
up = PTR(u);
vp = PTR(v);
if (usize >= 0)
{
if (vsize < 0)
return ~ (unsigned long) 0;
/* positive/positive */
if (usize < vsize)
MPN_SRCPTR_SWAP (up,usize, vp,vsize);
count = 0;
if (vsize != 0)
count = mpn_hamdist (up, vp, vsize);
usize -= vsize;
if (usize != 0)
count += mpn_popcount (up + vsize, usize);
return count;
}
else
{
mp_limb_t ulimb, vlimb;
mp_size_t old_vsize, step;
if (vsize >= 0)
return ~ (unsigned long) 0;
/* negative/negative */
usize = -usize;
vsize = -vsize;
/* skip common low zeros */
for (;;)
{
ASSERT (usize > 0);
ASSERT (vsize > 0);
usize--;
vsize--;
ulimb = *up++;
vlimb = *vp++;
if (ulimb != 0)
break;
if (vlimb != 0)
{
MPN_SRCPTR_SWAP (up,usize, vp,vsize);
ulimb = vlimb;
vlimb = 0;
break;
}
}
/* twos complement first non-zero limbs (ulimb is non-zero, but vlimb
might be zero) */
ulimb = -ulimb;
vlimb = -vlimb;
popc_limb (count, (ulimb ^ vlimb) & GMP_NUMB_MASK);
if (vlimb == 0)
{
unsigned long twoscount;
/* first non-zero of v */
old_vsize = vsize;
do
{
ASSERT (vsize > 0);
vsize--;
vlimb = *vp++;
}
while (vlimb == 0);
/* part of u corresponding to skipped v zeros */
step = old_vsize - vsize - 1;
count += step * GMP_NUMB_BITS;
step = MIN (step, usize);
if (step != 0)
{
count -= mpn_popcount (up, step);
usize -= step;
up += step;
}
/* First non-zero vlimb as twos complement, xor with ones
complement ulimb. Note -v^(~0^u) == (v-1)^u. */
vlimb--;
if (usize != 0)
{
usize--;
vlimb ^= *up++;
}
popc_limb (twoscount, vlimb);
count += twoscount;
}
/* Overlapping part of u and v, if any. Ones complement both, so just
plain hamdist. */
step = MIN (usize, vsize);
if (step != 0)
{
count += mpn_hamdist (up, vp, step);
usize -= step;
vsize -= step;
up += step;
vp += step;
}
/* Remaining high part of u or v, if any, ones complement but xor
against all ones in the other, so plain popcount. */
if (usize != 0)
{
remaining:
count += mpn_popcount (up, usize);
}
else if (vsize != 0)
{
up = vp;
usize = vsize;
goto remaining;
}
return count;
}
}
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