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/* mpz_hamdist -- calculate hamming distance.
Copyright 1994, 1996, 2001, 2002, 2009-2011 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 either:
* 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.
or
* the GNU General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any
later version.
or both in parallel, as here.
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 General Public License
for more details.
You should have received copies of the GNU General Public License and the
GNU Lesser General Public License along with the GNU MP Library. If not,
see https://www.gnu.org/licenses/. */
#include "gmp-impl.h"
mp_bitcnt_t
mpz_hamdist (mpz_srcptr u, mpz_srcptr v) __GMP_NOTHROW
{
mp_srcptr up, vp;
mp_size_t usize, vsize;
mp_bitcnt_t count;
usize = SIZ(u);
vsize = SIZ(v);
up = PTR(u);
vp = PTR(v);
if (usize >= 0)
{
if (vsize < 0)
return ~ (mp_bitcnt_t) 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 ~ (mp_bitcnt_t) 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)
{
mp_bitcnt_t 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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