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![Linus Torvalds](/assets/img/avatar_default.png)
Anything that generates a delta to see if two objects are close usually isn't interested in the delta ends up being bigger than some specified size, and this allows us to stop delta generation early when that happens.
412 lines
11 KiB
C
412 lines
11 KiB
C
/*
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* Copyright (C) 2005 Junio C Hamano
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*/
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#include "cache.h"
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#include "diff.h"
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#include "diffcore.h"
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#include "delta.h"
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#include "count-delta.h"
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/* Table of rename/copy destinations */
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static struct diff_rename_dst {
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struct diff_filespec *two;
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struct diff_filepair *pair;
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} *rename_dst;
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static int rename_dst_nr, rename_dst_alloc;
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static struct diff_rename_dst *locate_rename_dst(struct diff_filespec *two,
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int insert_ok)
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{
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int first, last;
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first = 0;
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last = rename_dst_nr;
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while (last > first) {
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int next = (last + first) >> 1;
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struct diff_rename_dst *dst = &(rename_dst[next]);
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int cmp = strcmp(two->path, dst->two->path);
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if (!cmp)
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return dst;
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if (cmp < 0) {
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last = next;
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continue;
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}
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first = next+1;
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}
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/* not found */
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if (!insert_ok)
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return NULL;
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/* insert to make it at "first" */
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if (rename_dst_alloc <= rename_dst_nr) {
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rename_dst_alloc = alloc_nr(rename_dst_alloc);
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rename_dst = xrealloc(rename_dst,
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rename_dst_alloc * sizeof(*rename_dst));
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}
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rename_dst_nr++;
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if (first < rename_dst_nr)
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memmove(rename_dst + first + 1, rename_dst + first,
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(rename_dst_nr - first - 1) * sizeof(*rename_dst));
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rename_dst[first].two = two;
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rename_dst[first].pair = NULL;
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return &(rename_dst[first]);
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}
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/* Table of rename/copy src files */
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static struct diff_rename_src {
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struct diff_filespec *one;
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unsigned src_stays : 1;
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} *rename_src;
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static int rename_src_nr, rename_src_alloc;
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static struct diff_rename_src *register_rename_src(struct diff_filespec *one,
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int src_stays)
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{
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int first, last;
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first = 0;
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last = rename_src_nr;
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while (last > first) {
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int next = (last + first) >> 1;
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struct diff_rename_src *src = &(rename_src[next]);
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int cmp = strcmp(one->path, src->one->path);
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if (!cmp)
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return src;
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if (cmp < 0) {
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last = next;
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continue;
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}
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first = next+1;
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}
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/* insert to make it at "first" */
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if (rename_src_alloc <= rename_src_nr) {
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rename_src_alloc = alloc_nr(rename_src_alloc);
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rename_src = xrealloc(rename_src,
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rename_src_alloc * sizeof(*rename_src));
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}
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rename_src_nr++;
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if (first < rename_src_nr)
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memmove(rename_src + first + 1, rename_src + first,
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(rename_src_nr - first - 1) * sizeof(*rename_src));
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rename_src[first].one = one;
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rename_src[first].src_stays = src_stays;
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return &(rename_src[first]);
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}
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static int is_exact_match(struct diff_filespec *src, struct diff_filespec *dst)
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{
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if (src->sha1_valid && dst->sha1_valid &&
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!memcmp(src->sha1, dst->sha1, 20))
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return 1;
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if (diff_populate_filespec(src, 1) || diff_populate_filespec(dst, 1))
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return 0;
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if (src->size != dst->size)
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return 0;
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if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0))
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return 0;
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if (src->size == dst->size &&
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!memcmp(src->data, dst->data, src->size))
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return 1;
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return 0;
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}
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struct diff_score {
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int src; /* index in rename_src */
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int dst; /* index in rename_dst */
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int score;
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};
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static int estimate_similarity(struct diff_filespec *src,
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struct diff_filespec *dst,
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int minimum_score)
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{
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/* src points at a file that existed in the original tree (or
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* optionally a file in the destination tree) and dst points
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* at a newly created file. They may be quite similar, in which
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* case we want to say src is renamed to dst or src is copied into
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* dst, and then some edit has been applied to dst.
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*
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* Compare them and return how similar they are, representing
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* the score as an integer between 0 and MAX_SCORE.
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*
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* When there is an exact match, it is considered a better
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* match than anything else; the destination does not even
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* call into this function in that case.
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*/
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void *delta;
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unsigned long delta_size, base_size, src_copied, literal_added;
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int score;
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/* We deal only with regular files. Symlink renames are handled
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* only when they are exact matches --- in other words, no edits
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* after renaming.
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*/
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if (!S_ISREG(src->mode) || !S_ISREG(dst->mode))
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return 0;
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delta_size = ((src->size < dst->size) ?
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(dst->size - src->size) : (src->size - dst->size));
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base_size = ((src->size < dst->size) ? src->size : dst->size);
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/* We would not consider edits that change the file size so
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* drastically. delta_size must be smaller than
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* (MAX_SCORE-minimum_score)/MAX_SCORE * min(src->size, dst->size).
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*
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* Note that base_size == 0 case is handled here already
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* and the final score computation below would not have a
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* divide-by-zero issue.
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*/
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if (base_size * (MAX_SCORE-minimum_score) < delta_size * MAX_SCORE)
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return 0;
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if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0))
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return 0; /* error but caught downstream */
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delta = diff_delta(src->data, src->size,
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dst->data, dst->size,
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&delta_size, ~0UL);
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/* A delta that has a lot of literal additions would have
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* big delta_size no matter what else it does.
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*/
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if (base_size * (MAX_SCORE-minimum_score) < delta_size * MAX_SCORE)
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return 0;
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/* Estimate the edit size by interpreting delta. */
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if (count_delta(delta, delta_size, &src_copied, &literal_added)) {
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free(delta);
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return 0;
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}
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free(delta);
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/* Extent of damage */
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if (src->size + literal_added < src_copied)
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delta_size = 0;
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else
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delta_size = (src->size - src_copied) + literal_added;
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/*
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* Now we will give some score to it. 100% edit gets 0 points
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* and 0% edit gets MAX_SCORE points.
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*/
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score = MAX_SCORE - (MAX_SCORE * delta_size / base_size);
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if (score < 0) return 0;
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if (MAX_SCORE < score) return MAX_SCORE;
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return score;
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}
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static void record_rename_pair(struct diff_queue_struct *renq,
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int dst_index, int src_index, int score)
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{
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struct diff_filespec *one, *two, *src, *dst;
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struct diff_filepair *dp;
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if (rename_dst[dst_index].pair)
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die("internal error: dst already matched.");
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src = rename_src[src_index].one;
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one = alloc_filespec(src->path);
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fill_filespec(one, src->sha1, src->mode);
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dst = rename_dst[dst_index].two;
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two = alloc_filespec(dst->path);
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fill_filespec(two, dst->sha1, dst->mode);
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dp = diff_queue(renq, one, two);
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dp->score = score;
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dp->source_stays = rename_src[src_index].src_stays;
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rename_dst[dst_index].pair = dp;
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}
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/*
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* We sort the rename similarity matrix with the score, in descending
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* order (the most similar first).
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*/
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static int score_compare(const void *a_, const void *b_)
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{
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const struct diff_score *a = a_, *b = b_;
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return b->score - a->score;
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}
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void diffcore_rename(int detect_rename, int minimum_score)
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{
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struct diff_queue_struct *q = &diff_queued_diff;
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struct diff_queue_struct renq, outq;
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struct diff_score *mx;
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int i, j;
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int num_create, num_src, dst_cnt;
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if (!minimum_score)
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minimum_score = DEFAULT_RENAME_SCORE;
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renq.queue = NULL;
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renq.nr = renq.alloc = 0;
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for (i = 0; i < q->nr; i++) {
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struct diff_filepair *p = q->queue[i];
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if (!DIFF_FILE_VALID(p->one))
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if (!DIFF_FILE_VALID(p->two))
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continue; /* unmerged */
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else
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locate_rename_dst(p->two, 1);
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else if (!DIFF_FILE_VALID(p->two)) {
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/* If the source is a broken "delete", and
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* they did not really want to get broken,
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* that means the source actually stays.
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*/
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int stays = (p->broken_pair && !p->score);
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register_rename_src(p->one, stays);
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}
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else if (detect_rename == DIFF_DETECT_COPY)
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register_rename_src(p->one, 1);
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}
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if (rename_dst_nr == 0)
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goto cleanup; /* nothing to do */
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/* We really want to cull the candidates list early
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* with cheap tests in order to avoid doing deltas.
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*/
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for (i = 0; i < rename_dst_nr; i++) {
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struct diff_filespec *two = rename_dst[i].two;
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for (j = 0; j < rename_src_nr; j++) {
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struct diff_filespec *one = rename_src[j].one;
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if (!is_exact_match(one, two))
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continue;
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record_rename_pair(&renq, i, j, MAX_SCORE);
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break; /* we are done with this entry */
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}
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}
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diff_debug_queue("done detecting exact", &renq);
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/* Have we run out the created file pool? If so we can avoid
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* doing the delta matrix altogether.
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*/
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if (renq.nr == rename_dst_nr)
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goto cleanup;
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num_create = (rename_dst_nr - renq.nr);
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num_src = rename_src_nr;
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mx = xmalloc(sizeof(*mx) * num_create * num_src);
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for (dst_cnt = i = 0; i < rename_dst_nr; i++) {
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int base = dst_cnt * num_src;
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struct diff_filespec *two = rename_dst[i].two;
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if (rename_dst[i].pair)
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continue; /* dealt with exact match already. */
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for (j = 0; j < rename_src_nr; j++) {
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struct diff_filespec *one = rename_src[j].one;
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struct diff_score *m = &mx[base+j];
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m->src = j;
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m->dst = i;
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m->score = estimate_similarity(one, two,
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minimum_score);
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}
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dst_cnt++;
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}
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/* cost matrix sorted by most to least similar pair */
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qsort(mx, num_create * num_src, sizeof(*mx), score_compare);
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for (i = 0; i < num_create * num_src; i++) {
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struct diff_rename_dst *dst = &rename_dst[mx[i].dst];
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if (dst->pair)
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continue; /* already done, either exact or fuzzy. */
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if (mx[i].score < minimum_score)
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break; /* there is no more usable pair. */
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record_rename_pair(&renq, mx[i].dst, mx[i].src, mx[i].score);
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}
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free(mx);
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diff_debug_queue("done detecting fuzzy", &renq);
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cleanup:
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/* At this point, we have found some renames and copies and they
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* are kept in renq. The original list is still in *q.
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*/
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outq.queue = NULL;
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outq.nr = outq.alloc = 0;
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for (i = 0; i < q->nr; i++) {
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struct diff_filepair *p = q->queue[i];
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struct diff_filepair *pair_to_free = NULL;
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if (!DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two)) {
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/*
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* Creation
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*
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* We would output this create record if it has
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* not been turned into a rename/copy already.
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*/
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struct diff_rename_dst *dst =
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locate_rename_dst(p->two, 0);
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if (dst && dst->pair) {
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diff_q(&outq, dst->pair);
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pair_to_free = p;
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}
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else
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/* no matching rename/copy source, so
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* record this as a creation.
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*/
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diff_q(&outq, p);
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}
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else if (DIFF_FILE_VALID(p->one) && !DIFF_FILE_VALID(p->two)) {
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/*
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* Deletion
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*
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* We would output this delete record if:
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*
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* (1) this is a broken delete and the counterpart
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* broken create remains in the output; or
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* (2) this is not a broken delete, and renq does
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* not have a rename/copy to move p->one->path
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* out.
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*
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* Otherwise, the counterpart broken create
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* has been turned into a rename-edit; or
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* delete did not have a matching create to
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* begin with.
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*/
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if (DIFF_PAIR_BROKEN(p)) {
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/* broken delete */
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struct diff_rename_dst *dst =
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locate_rename_dst(p->one, 0);
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if (dst && dst->pair)
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/* counterpart is now rename/copy */
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pair_to_free = p;
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}
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else {
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for (j = 0; j < renq.nr; j++)
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if (!strcmp(renq.queue[j]->one->path,
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p->one->path))
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break;
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if (j < renq.nr)
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/* this path remains */
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pair_to_free = p;
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}
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if (pair_to_free)
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;
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else
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diff_q(&outq, p);
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}
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else if (!diff_unmodified_pair(p))
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/* all the usual ones need to be kept */
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diff_q(&outq, p);
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else
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/* no need to keep unmodified pairs */
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pair_to_free = p;
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if (pair_to_free)
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diff_free_filepair(pair_to_free);
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}
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diff_debug_queue("done copying original", &outq);
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free(renq.queue);
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free(q->queue);
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*q = outq;
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diff_debug_queue("done collapsing", q);
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free(rename_dst);
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rename_dst = NULL;
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rename_dst_nr = rename_dst_alloc = 0;
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free(rename_src);
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rename_src = NULL;
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rename_src_nr = rename_src_alloc = 0;
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return;
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}
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