165 lines
3.9 KiB
C
165 lines
3.9 KiB
C
/* mpz_hamdist -- calculate hamming distance.
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Copyright 1994, 1996, 2001, 2002 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
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#include "mpir.h"
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#include "gmp-impl.h"
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mp_bitcnt_t
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mpz_hamdist (mpz_srcptr u, mpz_srcptr v)
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{
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mp_srcptr up, vp;
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mp_size_t usize, vsize;
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mp_bitcnt_t count;
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usize = SIZ(u);
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vsize = SIZ(v);
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up = PTR(u);
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vp = PTR(v);
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if (usize >= 0)
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{
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if (vsize < 0)
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return ~ (mp_bitcnt_t) 0;
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/* positive/positive */
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if (usize < vsize)
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MPN_SRCPTR_SWAP (up,usize, vp,vsize);
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count = 0;
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if (vsize != 0)
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count = mpn_hamdist (up, vp, vsize);
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usize -= vsize;
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if (usize != 0)
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count += mpn_popcount (up + vsize, usize);
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return count;
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}
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else
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{
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mp_limb_t ulimb, vlimb;
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mp_size_t old_vsize, step;
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if (vsize >= 0)
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return ~ (mp_limb_t) 0;
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/* negative/negative */
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usize = -usize;
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vsize = -vsize;
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/* skip common low zeros */
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for (;;)
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{
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ASSERT (usize > 0);
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ASSERT (vsize > 0);
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usize--;
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vsize--;
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ulimb = *up++;
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vlimb = *vp++;
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if (ulimb != 0)
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break;
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if (vlimb != 0)
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{
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MPN_SRCPTR_SWAP (up,usize, vp,vsize);
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ulimb = vlimb;
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vlimb = 0;
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break;
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}
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}
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/* twos complement first non-zero limbs (ulimb is non-zero, but vlimb
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might be zero) */
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ulimb = -ulimb;
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vlimb = -vlimb;
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popc_limb (count, (ulimb ^ vlimb) & GMP_NUMB_MASK);
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if (vlimb == 0)
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{
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mp_bitcnt_t twoscount;
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/* first non-zero of v */
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old_vsize = vsize;
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do
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{
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ASSERT (vsize > 0);
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vsize--;
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vlimb = *vp++;
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}
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while (vlimb == 0);
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/* part of u corresponding to skipped v zeros */
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step = old_vsize - vsize - 1;
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count += step * GMP_NUMB_BITS;
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step = MIN (step, usize);
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if (step != 0)
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{
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count -= mpn_popcount (up, step);
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usize -= step;
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up += step;
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}
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/* First non-zero vlimb as twos complement, xor with ones
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complement ulimb. Note -v^(~0^u) == (v-1)^u. */
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vlimb--;
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if (usize != 0)
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{
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usize--;
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vlimb ^= *up++;
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}
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popc_limb (twoscount, vlimb);
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count += twoscount;
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}
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/* Overlapping part of u and v, if any. Ones complement both, so just
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plain hamdist. */
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step = MIN (usize, vsize);
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if (step != 0)
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{
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count += mpn_hamdist (up, vp, step);
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usize -= step;
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vsize -= step;
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up += step;
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vp += step;
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}
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/* Remaining high part of u or v, if any, ones complement but xor
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against all ones in the other, so plain popcount. */
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if (usize != 0)
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{
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remaining:
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count += mpn_popcount (up, usize);
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}
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else if (vsize != 0)
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{
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up = vp;
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usize = vsize;
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goto remaining;
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}
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return count;
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}
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}
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