fd2bbdd238
This splits Geert's similarity fingerprint code into main program and fingerprinting function. The next step would be to try using this in pack-objects.c::try_delta() -- which would be a good evaluation. Signed-off-by: Junio C Hamano <junkio@cox.net>
155 lines
3.6 KiB
C
155 lines
3.6 KiB
C
/*
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*
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* Copyright (C) 1999 David Mazieres (dm@uun.org)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2, or (at
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* your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
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* USA
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*
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*/
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/* Faster generic_fls */
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/* (c) 2002, D.Phillips and Sistina Software */
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#include "rabinpoly.h"
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#define MSB64 0x8000000000000000ULL
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static inline unsigned fls8(unsigned n)
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{
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return n & 0xf0?
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n & 0xc0? (n >> 7) + 7: (n >> 5) + 5:
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n & 0x0c? (n >> 3) + 3: n - ((n + 1) >> 2);
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}
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static inline unsigned fls16(unsigned n)
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{
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return n & 0xff00? fls8(n >> 8) + 8: fls8(n);
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}
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static inline unsigned fls32(unsigned n)
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{
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return n & 0xffff0000? fls16(n >> 16) + 16: fls16(n);
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}
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static inline unsigned fls64(unsigned long long n) /* should be u64 */
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{
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return n & 0xffffffff00000000ULL? fls32(n >> 32) + 32: fls32(n);
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}
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static u_int64_t polymod (u_int64_t nh, u_int64_t nl, u_int64_t d);
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static void polymult (u_int64_t *php, u_int64_t *plp,
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u_int64_t x, u_int64_t y);
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static u_int64_t polymmult (u_int64_t x, u_int64_t y, u_int64_t d);
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static u_int64_t poly = 0xb15e234bd3792f63ull; // Actual polynomial
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static u_int64_t T[256]; // Lookup table for mod
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static int shift;
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u_int64_t append8 (u_int64_t p, u_char m)
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{ return ((p << 8) | m) ^ T[p >> shift];
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}
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static u_int64_t
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polymod (u_int64_t nh, u_int64_t nl, u_int64_t d)
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{ int i, k;
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assert (d);
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k = fls64 (d) - 1;
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d <<= 63 - k;
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if (nh) {
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if (nh & MSB64)
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nh ^= d;
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for (i = 62; i >= 0; i--)
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if (nh & 1ULL << i) {
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nh ^= d >> (63 - i);
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nl ^= d << (i + 1);
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}
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}
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for (i = 63; i >= k; i--)
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if (nl & 1ULL << i)
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nl ^= d >> (63 - i);
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return nl;
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}
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static void
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polymult (u_int64_t *php, u_int64_t *plp, u_int64_t x, u_int64_t y)
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{ int i;
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u_int64_t ph = 0, pl = 0;
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if (x & 1)
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pl = y;
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for (i = 1; i < 64; i++)
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if (x & (1ULL << i)) {
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ph ^= y >> (64 - i);
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pl ^= y << i;
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}
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if (php)
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*php = ph;
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if (plp)
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*plp = pl;
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}
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static u_int64_t
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polymmult (u_int64_t x, u_int64_t y, u_int64_t d)
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{
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u_int64_t h, l;
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polymult (&h, &l, x, y);
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return polymod (h, l, d);
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}
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static int size = RABIN_WINDOW_SIZE;
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static u_int64_t fingerprint = 0;
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static int bufpos = -1;
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static u_int64_t U[256];
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static u_char buf[RABIN_WINDOW_SIZE];
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void rabin_init ()
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{ u_int64_t sizeshift = 1;
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u_int64_t T1;
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int xshift;
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int i, j;
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assert (poly >= 0x100);
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xshift = fls64 (poly) - 1;
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shift = xshift - 8;
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T1 = polymod (0, 1ULL << xshift, poly);
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for (j = 0; j < 256; j++)
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T[j] = polymmult (j, T1, poly) | ((u_int64_t) j << xshift);
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for (i = 1; i < size; i++)
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sizeshift = append8 (sizeshift, 0);
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for (i = 0; i < 256; i++)
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U[i] = polymmult (i, sizeshift, poly);
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bzero (buf, sizeof (buf));
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}
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void
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rabin_reset ()
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{ rabin_init();
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fingerprint = 0;
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bzero (buf, sizeof (buf));
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}
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u_int64_t
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rabin_slide8 (u_char m)
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{ u_char om;
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if (++bufpos >= size) bufpos = 0;
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om = buf[bufpos];
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buf[bufpos] = m;
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fingerprint = append8 (fingerprint ^ U[om], m);
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return fingerprint;
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}
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