copy vs rename detection: avoid unnecessary O(n*m) loops

[git/git.git] / diffcore-rename.c

/*
 * Copyright (C) 2005 Junio C Hamano
 */
#include "cache.h"
#include "diff.h"
#include "diffcore.h"

/* Table of rename/copy destinations */

static struct diff_rename_dst {
	struct diff_filespec *two;
	struct diff_filepair *pair;
} *rename_dst;
static int rename_dst_nr, rename_dst_alloc;

static struct diff_rename_dst *locate_rename_dst(struct diff_filespec *two,
						 int insert_ok)
{
	int first, last;

	first = 0;
	last = rename_dst_nr;
	while (last > first) {
		int next = (last + first) >> 1;
		struct diff_rename_dst *dst = &(rename_dst[next]);
		int cmp = strcmp(two->path, dst->two->path);
		if (!cmp)
			return dst;
		if (cmp < 0) {
			last = next;
			continue;
		}
		first = next+1;
	}
	/* not found */
	if (!insert_ok)
		return NULL;
	/* insert to make it at "first" */
	if (rename_dst_alloc <= rename_dst_nr) {
		rename_dst_alloc = alloc_nr(rename_dst_alloc);
		rename_dst = xrealloc(rename_dst,
				      rename_dst_alloc * sizeof(*rename_dst));
	}
	rename_dst_nr++;
	if (first < rename_dst_nr)
		memmove(rename_dst + first + 1, rename_dst + first,
			(rename_dst_nr - first - 1) * sizeof(*rename_dst));
	rename_dst[first].two = alloc_filespec(two->path);
	fill_filespec(rename_dst[first].two, two->sha1, two->mode);
	rename_dst[first].pair = NULL;
	return &(rename_dst[first]);
}

/* Table of rename/copy src files */
static struct diff_rename_src {
	struct diff_filespec *one;
	unsigned short score; /* to remember the break score */
} *rename_src;
static int rename_src_nr, rename_src_alloc;

static struct diff_rename_src *register_rename_src(struct diff_filespec *one,
						   unsigned short score)
{
	int first, last;

	first = 0;
	last = rename_src_nr;
	while (last > first) {
		int next = (last + first) >> 1;
		struct diff_rename_src *src = &(rename_src[next]);
		int cmp = strcmp(one->path, src->one->path);
		if (!cmp)
			return src;
		if (cmp < 0) {
			last = next;
			continue;
		}
		first = next+1;
	}

	/* insert to make it at "first" */
	if (rename_src_alloc <= rename_src_nr) {
		rename_src_alloc = alloc_nr(rename_src_alloc);
		rename_src = xrealloc(rename_src,
				      rename_src_alloc * sizeof(*rename_src));
	}
	rename_src_nr++;
	if (first < rename_src_nr)
		memmove(rename_src + first + 1, rename_src + first,
			(rename_src_nr - first - 1) * sizeof(*rename_src));
	rename_src[first].one = one;
	rename_src[first].score = score;
	return &(rename_src[first]);
}

static int is_exact_match(struct diff_filespec *src,
			  struct diff_filespec *dst,
			  int contents_too)
{
	if (src->sha1_valid && dst->sha1_valid &&
	    !hashcmp(src->sha1, dst->sha1))
		return 1;
	if (!contents_too)
		return 0;
	if (diff_populate_filespec(src, 1) || diff_populate_filespec(dst, 1))
		return 0;
	if (src->size != dst->size)
		return 0;
	if (src->sha1_valid && dst->sha1_valid)
	    return !hashcmp(src->sha1, dst->sha1);
	if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0))
		return 0;
	if (src->size == dst->size &&
	    !memcmp(src->data, dst->data, src->size))
		return 1;
	return 0;
}

static int basename_same(struct diff_filespec *src, struct diff_filespec *dst)
{
	int src_len = strlen(src->path), dst_len = strlen(dst->path);
	while (src_len && dst_len) {
		char c1 = src->path[--src_len];
		char c2 = dst->path[--dst_len];
		if (c1 != c2)
			return 0;
		if (c1 == '/')
			return 1;
	}
	return (!src_len || src->path[src_len - 1] == '/') &&
		(!dst_len || dst->path[dst_len - 1] == '/');
}

struct diff_score {
	int src; /* index in rename_src */
	int dst; /* index in rename_dst */
	int score;
	int name_score;
};

static int estimate_similarity(struct diff_filespec *src,
			       struct diff_filespec *dst,
			       int minimum_score)
{
	/* src points at a file that existed in the original tree (or
	 * optionally a file in the destination tree) and dst points
	 * at a newly created file.  They may be quite similar, in which
	 * case we want to say src is renamed to dst or src is copied into
	 * dst, and then some edit has been applied to dst.
	 *
	 * Compare them and return how similar they are, representing
	 * the score as an integer between 0 and MAX_SCORE.
	 *
	 * When there is an exact match, it is considered a better
	 * match than anything else; the destination does not even
	 * call into this function in that case.
	 */
	unsigned long max_size, delta_size, base_size, src_copied, literal_added;
	unsigned long delta_limit;
	int score;

	/* We deal only with regular files.  Symlink renames are handled
	 * only when they are exact matches --- in other words, no edits
	 * after renaming.
	 */
	if (!S_ISREG(src->mode) || !S_ISREG(dst->mode))
		return 0;

	max_size = ((src->size > dst->size) ? src->size : dst->size);
	base_size = ((src->size < dst->size) ? src->size : dst->size);
	delta_size = max_size - base_size;

	/* We would not consider edits that change the file size so
	 * drastically.  delta_size must be smaller than
	 * (MAX_SCORE-minimum_score)/MAX_SCORE * min(src->size, dst->size).
	 *
	 * Note that base_size == 0 case is handled here already
	 * and the final score computation below would not have a
	 * divide-by-zero issue.
	 */
	if (base_size * (MAX_SCORE-minimum_score) < delta_size * MAX_SCORE)
		return 0;

	if ((!src->cnt_data && diff_populate_filespec(src, 0))
		|| (!dst->cnt_data && diff_populate_filespec(dst, 0)))
		return 0; /* error but caught downstream */


	delta_limit = (unsigned long)
		(base_size * (MAX_SCORE-minimum_score) / MAX_SCORE);
	if (diffcore_count_changes(src, dst,
				   &src->cnt_data, &dst->cnt_data,
				   delta_limit,
				   &src_copied, &literal_added))
		return 0;

	/* How similar are they?
	 * what percentage of material in dst are from source?
	 */
	if (!dst->size)
		score = 0; /* should not happen */
	else
		score = (int)(src_copied * MAX_SCORE / max_size);
	return score;
}

static void record_rename_pair(int dst_index, int src_index, int score)
{
	struct diff_filespec *src, *dst;
	struct diff_filepair *dp;

	if (rename_dst[dst_index].pair)
		die("internal error: dst already matched.");

	src = rename_src[src_index].one;
	src->rename_used++;
	src->count++;

	dst = rename_dst[dst_index].two;
	dst->count++;

	dp = diff_queue(NULL, src, dst);
	dp->renamed_pair = 1;
	if (!strcmp(src->path, dst->path))
		dp->score = rename_src[src_index].score;
	else
		dp->score = score;
	rename_dst[dst_index].pair = dp;
}

/*
 * We sort the rename similarity matrix with the score, in descending
 * order (the most similar first).
 */
static int score_compare(const void *a_, const void *b_)
{
	const struct diff_score *a = a_, *b = b_;

	if (a->score == b->score)
		return b->name_score - a->name_score;

	return b->score - a->score;
}

/*
 * Find exact renames first.
 *
 * The first round matches up the up-to-date entries,
 * and then during the second round we try to match
 * cache-dirty entries as well.
 *
 * Note: the rest of the rename logic depends on this
 * phase also populating all the filespecs for any
 * entry that isn't matched up with an exact rename,
 * see "is_exact_match()".
 */
static int find_exact_renames(void)
{
	int rename_count = 0;
	int contents_too;

	for (contents_too = 0; contents_too < 2; contents_too++) {
		int i;

		for (i = 0; i < rename_dst_nr; i++) {
			struct diff_filespec *two = rename_dst[i].two;
			int j;

			if (rename_dst[i].pair)
				continue; /* dealt with an earlier round */
			for (j = 0; j < rename_src_nr; j++) {
				int k;
				struct diff_filespec *one = rename_src[j].one;
				if (!is_exact_match(one, two, contents_too))
					continue;

				/* see if there is a basename match, too */
				for (k = j; k < rename_src_nr; k++) {
					one = rename_src[k].one;
					if (basename_same(one, two) &&
						is_exact_match(one, two,
							contents_too)) {
						j = k;
						break;
					}
				}

				record_rename_pair(i, j, (int)MAX_SCORE);
				rename_count++;
				break; /* we are done with this entry */
			}
		}
	}
	return rename_count;
}

void diffcore_rename(struct diff_options *options)
{
	int detect_rename = options->detect_rename;
	int minimum_score = options->rename_score;
	int rename_limit = options->rename_limit;
	struct diff_queue_struct *q = &diff_queued_diff;
	struct diff_queue_struct outq;
	struct diff_score *mx;
	int i, j, rename_count;
	int num_create, num_src, dst_cnt;

	if (!minimum_score)
		minimum_score = DEFAULT_RENAME_SCORE;

	for (i = 0; i < q->nr; i++) {
		struct diff_filepair *p = q->queue[i];
		if (!DIFF_FILE_VALID(p->one)) {
			if (!DIFF_FILE_VALID(p->two))
				continue; /* unmerged */
			else if (options->single_follow &&
				 strcmp(options->single_follow, p->two->path))
				continue; /* not interested */
			else
				locate_rename_dst(p->two, 1);
		}
		else if (!DIFF_FILE_VALID(p->two)) {
			/*
			 * If the source is a broken "delete", and
			 * they did not really want to get broken,
			 * that means the source actually stays.
			 * So we increment the "rename_used" score
			 * by one, to indicate ourselves as a user
			 */
			if (p->broken_pair && !p->score)
				p->one->rename_used++;
			register_rename_src(p->one, p->score);
		}
		else if (detect_rename == DIFF_DETECT_COPY) {
			/*
			 * Increment the "rename_used" score by
			 * one, to indicate ourselves as a user.
			 */
			p->one->rename_used++;
			register_rename_src(p->one, p->score);
		}
	}
	if (rename_dst_nr == 0 || rename_src_nr == 0)
		goto cleanup; /* nothing to do */

	/*
	 * This basically does a test for the rename matrix not
	 * growing larger than a "rename_limit" square matrix, ie:
	 *
	 *    rename_dst_nr * rename_src_nr > rename_limit * rename_limit
	 *
	 * but handles the potential overflow case specially (and we
	 * assume at least 32-bit integers)
	 */
	if (rename_limit <= 0 || rename_limit > 32767)
		rename_limit = 32767;
	if (rename_dst_nr > rename_limit && rename_src_nr > rename_limit)
		goto cleanup;
	if (rename_dst_nr * rename_src_nr > rename_limit * rename_limit)
		goto cleanup;

	/*
	 * We really want to cull the candidates list early
	 * with cheap tests in order to avoid doing deltas.
	 */
	rename_count = find_exact_renames();

	/* Have we run out the created file pool?  If so we can avoid
	 * doing the delta matrix altogether.
	 */
	if (rename_count == rename_dst_nr)
		goto cleanup;

	if (minimum_score == MAX_SCORE)
		goto cleanup;

	num_create = (rename_dst_nr - rename_count);
	num_src = rename_src_nr;
	mx = xmalloc(sizeof(*mx) * num_create * num_src);
	for (dst_cnt = i = 0; i < rename_dst_nr; i++) {
		int base = dst_cnt * num_src;
		struct diff_filespec *two = rename_dst[i].two;
		if (rename_dst[i].pair)
			continue; /* dealt with exact match already. */
		for (j = 0; j < rename_src_nr; j++) {
			struct diff_filespec *one = rename_src[j].one;
			struct diff_score *m = &mx[base+j];
			m->src = j;
			m->dst = i;
			m->score = estimate_similarity(one, two,
						       minimum_score);
			m->name_score = basename_same(one, two);
			diff_free_filespec_blob(one);
		}
		/* We do not need the text anymore */
		diff_free_filespec_blob(two);
		dst_cnt++;
	}
	/* cost matrix sorted by most to least similar pair */
	qsort(mx, num_create * num_src, sizeof(*mx), score_compare);
	for (i = 0; i < num_create * num_src; i++) {
		struct diff_rename_dst *dst = &rename_dst[mx[i].dst];
		if (dst->pair)
			continue; /* already done, either exact or fuzzy. */
		if (mx[i].score < minimum_score)
			break; /* there is no more usable pair. */
		record_rename_pair(mx[i].dst, mx[i].src, mx[i].score);
		rename_count++;
	}
	free(mx);

 cleanup:
	/* At this point, we have found some renames and copies and they
	 * are recorded in rename_dst.  The original list is still in *q.
	 */
	outq.queue = NULL;
	outq.nr = outq.alloc = 0;
	for (i = 0; i < q->nr; i++) {
		struct diff_filepair *p = q->queue[i];
		struct diff_filepair *pair_to_free = NULL;

		if (!DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two)) {
			/*
			 * Creation
			 *
			 * We would output this create record if it has
			 * not been turned into a rename/copy already.
			 */
			struct diff_rename_dst *dst =
				locate_rename_dst(p->two, 0);
			if (dst && dst->pair) {
				diff_q(&outq, dst->pair);
				pair_to_free = p;
			}
			else
				/* no matching rename/copy source, so
				 * record this as a creation.
				 */
				diff_q(&outq, p);
		}
		else if (DIFF_FILE_VALID(p->one) && !DIFF_FILE_VALID(p->two)) {
			/*
			 * Deletion
			 *
			 * We would output this delete record if:
			 *
			 * (1) this is a broken delete and the counterpart
			 *     broken create remains in the output; or
			 * (2) this is not a broken delete, and rename_dst
			 *     does not have a rename/copy to move p->one->path
			 *     out of existence.
			 *
			 * Otherwise, the counterpart broken create
			 * has been turned into a rename-edit; or
			 * delete did not have a matching create to
			 * begin with.
			 */
			if (DIFF_PAIR_BROKEN(p)) {
				/* broken delete */
				struct diff_rename_dst *dst =
					locate_rename_dst(p->one, 0);
				if (dst && dst->pair)
					/* counterpart is now rename/copy */
					pair_to_free = p;
			}
			else {
				if (p->one->rename_used)
					/* this path remains */
					pair_to_free = p;
			}

			if (pair_to_free)
				;
			else
				diff_q(&outq, p);
		}
		else if (!diff_unmodified_pair(p))
			/* all the usual ones need to be kept */
			diff_q(&outq, p);
		else
			/* no need to keep unmodified pairs */
			pair_to_free = p;

		if (pair_to_free)
			diff_free_filepair(pair_to_free);
	}
	diff_debug_queue("done copying original", &outq);

	free(q->queue);
	*q = outq;
	diff_debug_queue("done collapsing", q);

	for (i = 0; i < rename_dst_nr; i++)
		free_filespec(rename_dst[i].two);

	free(rename_dst);
	rename_dst = NULL;
	rename_dst_nr = rename_dst_alloc = 0;
	free(rename_src);
	rename_src = NULL;
	rename_src_nr = rename_src_alloc = 0;
	return;
}