popham.c
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上传日期:2022-08-06
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- /* mpn_popcount, mpn_hamdist -- mpn bit population count/hamming distance.
- Copyright 1994, 1996, 2000, 2001, 2002, 2005 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"
- #if OPERATION_popcount
- #define FNAME mpn_popcount
- #define POPHAM(u,v) u
- #endif
- #if OPERATION_hamdist
- #define FNAME mpn_hamdist
- #define POPHAM(u,v) u ^ v
- #endif
- mp_bitcnt_t
- FNAME (mp_srcptr up,
- #if OPERATION_hamdist
- mp_srcptr vp,
- #endif
- mp_size_t n)
- {
- mp_bitcnt_t result = 0;
- mp_limb_t p0, p1, p2, p3, x, p01, p23;
- mp_size_t i;
- ASSERT (n >= 1); /* Actually, this code handles any n, but some
- assembly implementations do not. */
- for (i = n >> 2; i != 0; i--)
- {
- p0 = POPHAM (up[0], vp[0]);
- p0 -= (p0 >> 1) & MP_LIMB_T_MAX/3; /* 2 0-2 */
- p0 = ((p0 >> 2) & MP_LIMB_T_MAX/5) + (p0 & MP_LIMB_T_MAX/5); /* 4 0-4 */
- p1 = POPHAM (up[1], vp[1]);
- p1 -= (p1 >> 1) & MP_LIMB_T_MAX/3; /* 2 0-2 */
- p1 = ((p1 >> 2) & MP_LIMB_T_MAX/5) + (p1 & MP_LIMB_T_MAX/5); /* 4 0-4 */
- p01 = p0 + p1; /* 8 0-8 */
- p01 = ((p01 >> 4) & MP_LIMB_T_MAX/17) + (p01 & MP_LIMB_T_MAX/17); /* 8 0-16 */
- p2 = POPHAM (up[2], vp[2]);
- p2 -= (p2 >> 1) & MP_LIMB_T_MAX/3; /* 2 0-2 */
- p2 = ((p2 >> 2) & MP_LIMB_T_MAX/5) + (p2 & MP_LIMB_T_MAX/5); /* 4 0-4 */
- p3 = POPHAM (up[3], vp[3]);
- p3 -= (p3 >> 1) & MP_LIMB_T_MAX/3; /* 2 0-2 */
- p3 = ((p3 >> 2) & MP_LIMB_T_MAX/5) + (p3 & MP_LIMB_T_MAX/5); /* 4 0-4 */
- p23 = p2 + p3; /* 8 0-8 */
- p23 = ((p23 >> 4) & MP_LIMB_T_MAX/17) + (p23 & MP_LIMB_T_MAX/17); /* 8 0-16 */
- x = p01 + p23; /* 8 0-32 */
- x = (x >> 8) + x; /* 8 0-64 */
- x = (x >> 16) + x; /* 8 0-128 */
- #if GMP_LIMB_BITS > 32
- x = ((x >> 32) & 0xff) + (x & 0xff); /* 8 0-256 */
- result += x;
- #else
- result += x & 0xff;
- #endif
- up += 4;
- #if OPERATION_hamdist
- vp += 4;
- #endif
- }
- n &= 3;
- if (n != 0)
- {
- x = 0;
- do
- {
- p0 = POPHAM (up[0], vp[0]);
- p0 -= (p0 >> 1) & MP_LIMB_T_MAX/3; /* 2 0-2 */
- p0 = ((p0 >> 2) & MP_LIMB_T_MAX/5) + (p0 & MP_LIMB_T_MAX/5); /* 4 0-4 */
- p0 = ((p0 >> 4) + p0) & MP_LIMB_T_MAX/17; /* 8 0-8 */
- x += p0;
- up += 1;
- #if OPERATION_hamdist
- vp += 1;
- #endif
- }
- while (--n);
- x = (x >> 8) + x;
- x = (x >> 16) + x;
- #if GMP_LIMB_BITS > 32
- x = (x >> 32) + x;
- #endif
- result += x & 0xff;
- }
- return result;
- }