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![Tay Ray Chuan](/assets/img/avatar_default.png)
This is in preparation for the histogram diff algorithm, which will also re-use much of the code to call the default Meyers diff algorithm. Signed-off-by: Tay Ray Chuan <rctay89@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
359 lines
9.9 KiB
C
359 lines
9.9 KiB
C
/*
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* LibXDiff by Davide Libenzi ( File Differential Library )
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* Copyright (C) 2003-2009 Davide Libenzi, Johannes E. Schindelin
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but 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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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*
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* Davide Libenzi <davidel@xmailserver.org>
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*
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*/
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#include "xinclude.h"
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#include "xtypes.h"
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#include "xdiff.h"
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/*
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* The basic idea of patience diff is to find lines that are unique in
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* both files. These are intuitively the ones that we want to see as
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* common lines.
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*
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* The maximal ordered sequence of such line pairs (where ordered means
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* that the order in the sequence agrees with the order of the lines in
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* both files) naturally defines an initial set of common lines.
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*
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* Now, the algorithm tries to extend the set of common lines by growing
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* the line ranges where the files have identical lines.
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*
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* Between those common lines, the patience diff algorithm is applied
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* recursively, until no unique line pairs can be found; these line ranges
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* are handled by the well-known Myers algorithm.
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*/
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#define NON_UNIQUE ULONG_MAX
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/*
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* This is a hash mapping from line hash to line numbers in the first and
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* second file.
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*/
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struct hashmap {
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int nr, alloc;
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struct entry {
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unsigned long hash;
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/*
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* 0 = unused entry, 1 = first line, 2 = second, etc.
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* line2 is NON_UNIQUE if the line is not unique
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* in either the first or the second file.
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*/
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unsigned long line1, line2;
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/*
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* "next" & "previous" are used for the longest common
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* sequence;
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* initially, "next" reflects only the order in file1.
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*/
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struct entry *next, *previous;
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} *entries, *first, *last;
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/* were common records found? */
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unsigned long has_matches;
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mmfile_t *file1, *file2;
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xdfenv_t *env;
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xpparam_t const *xpp;
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};
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/* The argument "pass" is 1 for the first file, 2 for the second. */
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static void insert_record(int line, struct hashmap *map, int pass)
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{
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xrecord_t **records = pass == 1 ?
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map->env->xdf1.recs : map->env->xdf2.recs;
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xrecord_t *record = records[line - 1], *other;
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/*
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* After xdl_prepare_env() (or more precisely, due to
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* xdl_classify_record()), the "ha" member of the records (AKA lines)
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* is _not_ the hash anymore, but a linearized version of it. In
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* other words, the "ha" member is guaranteed to start with 0 and
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* the second record's ha can only be 0 or 1, etc.
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*
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* So we multiply ha by 2 in the hope that the hashing was
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* "unique enough".
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*/
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int index = (int)((record->ha << 1) % map->alloc);
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while (map->entries[index].line1) {
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other = map->env->xdf1.recs[map->entries[index].line1 - 1];
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if (map->entries[index].hash != record->ha ||
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!xdl_recmatch(record->ptr, record->size,
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other->ptr, other->size,
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map->xpp->flags)) {
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if (++index >= map->alloc)
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index = 0;
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continue;
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}
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if (pass == 2)
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map->has_matches = 1;
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if (pass == 1 || map->entries[index].line2)
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map->entries[index].line2 = NON_UNIQUE;
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else
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map->entries[index].line2 = line;
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return;
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}
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if (pass == 2)
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return;
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map->entries[index].line1 = line;
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map->entries[index].hash = record->ha;
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if (!map->first)
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map->first = map->entries + index;
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if (map->last) {
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map->last->next = map->entries + index;
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map->entries[index].previous = map->last;
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}
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map->last = map->entries + index;
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map->nr++;
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}
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/*
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* This function has to be called for each recursion into the inter-hunk
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* parts, as previously non-unique lines can become unique when being
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* restricted to a smaller part of the files.
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*
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* It is assumed that env has been prepared using xdl_prepare().
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*/
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static int fill_hashmap(mmfile_t *file1, mmfile_t *file2,
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xpparam_t const *xpp, xdfenv_t *env,
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struct hashmap *result,
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int line1, int count1, int line2, int count2)
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{
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result->file1 = file1;
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result->file2 = file2;
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result->xpp = xpp;
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result->env = env;
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/* We know exactly how large we want the hash map */
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result->alloc = count1 * 2;
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result->entries = (struct entry *)
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xdl_malloc(result->alloc * sizeof(struct entry));
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if (!result->entries)
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return -1;
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memset(result->entries, 0, result->alloc * sizeof(struct entry));
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/* First, fill with entries from the first file */
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while (count1--)
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insert_record(line1++, result, 1);
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/* Then search for matches in the second file */
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while (count2--)
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insert_record(line2++, result, 2);
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return 0;
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}
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/*
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* Find the longest sequence with a smaller last element (meaning a smaller
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* line2, as we construct the sequence with entries ordered by line1).
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*/
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static int binary_search(struct entry **sequence, int longest,
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struct entry *entry)
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{
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int left = -1, right = longest;
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while (left + 1 < right) {
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int middle = (left + right) / 2;
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/* by construction, no two entries can be equal */
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if (sequence[middle]->line2 > entry->line2)
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right = middle;
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else
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left = middle;
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}
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/* return the index in "sequence", _not_ the sequence length */
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return left;
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}
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/*
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* The idea is to start with the list of common unique lines sorted by
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* the order in file1. For each of these pairs, the longest (partial)
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* sequence whose last element's line2 is smaller is determined.
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*
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* For efficiency, the sequences are kept in a list containing exactly one
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* item per sequence length: the sequence with the smallest last
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* element (in terms of line2).
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*/
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static struct entry *find_longest_common_sequence(struct hashmap *map)
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{
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struct entry **sequence = xdl_malloc(map->nr * sizeof(struct entry *));
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int longest = 0, i;
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struct entry *entry;
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for (entry = map->first; entry; entry = entry->next) {
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if (!entry->line2 || entry->line2 == NON_UNIQUE)
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continue;
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i = binary_search(sequence, longest, entry);
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entry->previous = i < 0 ? NULL : sequence[i];
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sequence[++i] = entry;
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if (i == longest)
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longest++;
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}
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/* No common unique lines were found */
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if (!longest) {
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xdl_free(sequence);
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return NULL;
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}
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/* Iterate starting at the last element, adjusting the "next" members */
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entry = sequence[longest - 1];
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entry->next = NULL;
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while (entry->previous) {
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entry->previous->next = entry;
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entry = entry->previous;
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}
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xdl_free(sequence);
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return entry;
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}
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static int match(struct hashmap *map, int line1, int line2)
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{
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xrecord_t *record1 = map->env->xdf1.recs[line1 - 1];
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xrecord_t *record2 = map->env->xdf2.recs[line2 - 1];
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return xdl_recmatch(record1->ptr, record1->size,
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record2->ptr, record2->size, map->xpp->flags);
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}
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static int patience_diff(mmfile_t *file1, mmfile_t *file2,
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xpparam_t const *xpp, xdfenv_t *env,
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int line1, int count1, int line2, int count2);
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static int walk_common_sequence(struct hashmap *map, struct entry *first,
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int line1, int count1, int line2, int count2)
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{
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int end1 = line1 + count1, end2 = line2 + count2;
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int next1, next2;
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for (;;) {
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/* Try to grow the line ranges of common lines */
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if (first) {
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next1 = first->line1;
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next2 = first->line2;
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while (next1 > line1 && next2 > line2 &&
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match(map, next1 - 1, next2 - 1)) {
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next1--;
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next2--;
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}
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} else {
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next1 = end1;
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next2 = end2;
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}
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while (line1 < next1 && line2 < next2 &&
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match(map, line1, line2)) {
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line1++;
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line2++;
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}
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/* Recurse */
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if (next1 > line1 || next2 > line2) {
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struct hashmap submap;
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memset(&submap, 0, sizeof(submap));
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if (patience_diff(map->file1, map->file2,
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map->xpp, map->env,
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line1, next1 - line1,
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line2, next2 - line2))
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return -1;
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}
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if (!first)
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return 0;
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while (first->next &&
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first->next->line1 == first->line1 + 1 &&
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first->next->line2 == first->line2 + 1)
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first = first->next;
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line1 = first->line1 + 1;
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line2 = first->line2 + 1;
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first = first->next;
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}
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}
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static int fall_back_to_classic_diff(struct hashmap *map,
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int line1, int count1, int line2, int count2)
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{
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xpparam_t xpp;
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xpp.flags = map->xpp->flags & ~XDF_PATIENCE_DIFF;
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return xdl_fall_back_diff(map->env, &xpp,
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line1, count1, line2, count2);
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}
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/*
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* Recursively find the longest common sequence of unique lines,
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* and if none was found, ask xdl_do_diff() to do the job.
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*
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* This function assumes that env was prepared with xdl_prepare_env().
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*/
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static int patience_diff(mmfile_t *file1, mmfile_t *file2,
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xpparam_t const *xpp, xdfenv_t *env,
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int line1, int count1, int line2, int count2)
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{
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struct hashmap map;
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struct entry *first;
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int result = 0;
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/* trivial case: one side is empty */
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if (!count1) {
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while(count2--)
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env->xdf2.rchg[line2++ - 1] = 1;
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return 0;
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} else if (!count2) {
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while(count1--)
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env->xdf1.rchg[line1++ - 1] = 1;
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return 0;
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}
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memset(&map, 0, sizeof(map));
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if (fill_hashmap(file1, file2, xpp, env, &map,
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line1, count1, line2, count2))
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return -1;
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/* are there any matching lines at all? */
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if (!map.has_matches) {
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while(count1--)
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env->xdf1.rchg[line1++ - 1] = 1;
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while(count2--)
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env->xdf2.rchg[line2++ - 1] = 1;
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xdl_free(map.entries);
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return 0;
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}
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first = find_longest_common_sequence(&map);
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if (first)
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result = walk_common_sequence(&map, first,
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line1, count1, line2, count2);
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else
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result = fall_back_to_classic_diff(&map,
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line1, count1, line2, count2);
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xdl_free(map.entries);
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return result;
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}
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int xdl_do_patience_diff(mmfile_t *file1, mmfile_t *file2,
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xpparam_t const *xpp, xdfenv_t *env)
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{
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if (xdl_prepare_env(file1, file2, xpp, env) < 0)
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return -1;
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/* environment is cleaned up in xdl_diff() */
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return patience_diff(file1, file2, xpp, env,
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1, env->xdf1.nrec, 1, env->xdf2.nrec);
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}
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