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https://github.com/git/git.git
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2c5495f7b6
Avoid scanning strings twice, once with strchr() and then with strlen(), by using strchrnul(). Helped-by: Junio C Hamano <gitster@pobox.com> Signed-off-by: Rohit Mani <rohit.mani@outlook.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
350 lines
8.2 KiB
C
350 lines
8.2 KiB
C
#include "cache.h"
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#include "tree.h"
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#include "tree-walk.h"
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static int score_missing(unsigned mode, const char *path)
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{
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int score;
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if (S_ISDIR(mode))
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score = -1000;
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else if (S_ISLNK(mode))
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score = -500;
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else
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score = -50;
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return score;
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}
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static int score_differs(unsigned mode1, unsigned mode2, const char *path)
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{
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int score;
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if (S_ISDIR(mode1) != S_ISDIR(mode2))
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score = -100;
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else if (S_ISLNK(mode1) != S_ISLNK(mode2))
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score = -50;
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else
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score = -5;
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return score;
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}
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static int score_matches(unsigned mode1, unsigned mode2, const char *path)
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{
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int score;
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/* Heh, we found SHA-1 collisions between different kind of objects */
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if (S_ISDIR(mode1) != S_ISDIR(mode2))
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score = -100;
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else if (S_ISLNK(mode1) != S_ISLNK(mode2))
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score = -50;
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else if (S_ISDIR(mode1))
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score = 1000;
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else if (S_ISLNK(mode1))
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score = 500;
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else
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score = 250;
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return score;
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}
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static void *fill_tree_desc_strict(struct tree_desc *desc,
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const unsigned char *hash)
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{
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void *buffer;
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enum object_type type;
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unsigned long size;
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buffer = read_sha1_file(hash, &type, &size);
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if (!buffer)
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die("unable to read tree (%s)", sha1_to_hex(hash));
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if (type != OBJ_TREE)
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die("%s is not a tree", sha1_to_hex(hash));
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init_tree_desc(desc, buffer, size);
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return buffer;
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}
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static int base_name_entries_compare(const struct name_entry *a,
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const struct name_entry *b)
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{
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return base_name_compare(a->path, tree_entry_len(a), a->mode,
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b->path, tree_entry_len(b), b->mode);
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}
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/*
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* Inspect two trees, and give a score that tells how similar they are.
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*/
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static int score_trees(const unsigned char *hash1, const unsigned char *hash2)
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{
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struct tree_desc one;
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struct tree_desc two;
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void *one_buf = fill_tree_desc_strict(&one, hash1);
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void *two_buf = fill_tree_desc_strict(&two, hash2);
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int score = 0;
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for (;;) {
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struct name_entry e1, e2;
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int got_entry_from_one = tree_entry(&one, &e1);
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int got_entry_from_two = tree_entry(&two, &e2);
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int cmp;
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if (got_entry_from_one && got_entry_from_two)
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cmp = base_name_entries_compare(&e1, &e2);
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else if (got_entry_from_one)
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/* two lacks this entry */
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cmp = -1;
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else if (got_entry_from_two)
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/* two has more entries */
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cmp = 1;
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else
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break;
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if (cmp < 0)
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/* path1 does not appear in two */
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score += score_missing(e1.mode, e1.path);
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else if (cmp > 0)
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/* path2 does not appear in one */
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score += score_missing(e2.mode, e2.path);
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else if (hashcmp(e1.sha1, e2.sha1))
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/* they are different */
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score += score_differs(e1.mode, e2.mode, e1.path);
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else
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/* same subtree or blob */
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score += score_matches(e1.mode, e2.mode, e1.path);
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}
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free(one_buf);
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free(two_buf);
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return score;
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}
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/*
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* Match one itself and its subtrees with two and pick the best match.
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*/
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static void match_trees(const unsigned char *hash1,
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const unsigned char *hash2,
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int *best_score,
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char **best_match,
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const char *base,
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int recurse_limit)
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{
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struct tree_desc one;
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void *one_buf = fill_tree_desc_strict(&one, hash1);
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while (one.size) {
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const char *path;
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const unsigned char *elem;
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unsigned mode;
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int score;
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elem = tree_entry_extract(&one, &path, &mode);
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if (!S_ISDIR(mode))
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goto next;
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score = score_trees(elem, hash2);
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if (*best_score < score) {
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char *newpath;
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newpath = xmalloc(strlen(base) + strlen(path) + 1);
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sprintf(newpath, "%s%s", base, path);
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free(*best_match);
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*best_match = newpath;
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*best_score = score;
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}
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if (recurse_limit) {
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char *newbase;
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newbase = xmalloc(strlen(base) + strlen(path) + 2);
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sprintf(newbase, "%s%s/", base, path);
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match_trees(elem, hash2, best_score, best_match,
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newbase, recurse_limit - 1);
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free(newbase);
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}
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next:
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update_tree_entry(&one);
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}
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free(one_buf);
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}
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/*
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* A tree "hash1" has a subdirectory at "prefix". Come up with a
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* tree object by replacing it with another tree "hash2".
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*/
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static int splice_tree(const unsigned char *hash1,
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const char *prefix,
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const unsigned char *hash2,
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unsigned char *result)
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{
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char *subpath;
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int toplen;
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char *buf;
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unsigned long sz;
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struct tree_desc desc;
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unsigned char *rewrite_here;
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const unsigned char *rewrite_with;
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unsigned char subtree[20];
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enum object_type type;
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int status;
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subpath = strchrnul(prefix, '/');
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toplen = subpath - prefix;
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if (*subpath)
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subpath++;
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buf = read_sha1_file(hash1, &type, &sz);
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if (!buf)
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die("cannot read tree %s", sha1_to_hex(hash1));
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init_tree_desc(&desc, buf, sz);
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rewrite_here = NULL;
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while (desc.size) {
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const char *name;
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unsigned mode;
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const unsigned char *sha1;
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sha1 = tree_entry_extract(&desc, &name, &mode);
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if (strlen(name) == toplen &&
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!memcmp(name, prefix, toplen)) {
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if (!S_ISDIR(mode))
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die("entry %s in tree %s is not a tree",
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name, sha1_to_hex(hash1));
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rewrite_here = (unsigned char *) sha1;
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break;
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}
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update_tree_entry(&desc);
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}
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if (!rewrite_here)
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die("entry %.*s not found in tree %s",
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toplen, prefix, sha1_to_hex(hash1));
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if (*subpath) {
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status = splice_tree(rewrite_here, subpath, hash2, subtree);
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if (status)
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return status;
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rewrite_with = subtree;
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}
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else
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rewrite_with = hash2;
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hashcpy(rewrite_here, rewrite_with);
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status = write_sha1_file(buf, sz, tree_type, result);
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free(buf);
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return status;
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}
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/*
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* We are trying to come up with a merge between one and two that
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* results in a tree shape similar to one. The tree two might
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* correspond to a subtree of one, in which case it needs to be
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* shifted down by prefixing otherwise empty directories. On the
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* other hand, it could cover tree one and we might need to pick a
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* subtree of it.
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*/
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void shift_tree(const unsigned char *hash1,
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const unsigned char *hash2,
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unsigned char *shifted,
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int depth_limit)
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{
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char *add_prefix;
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char *del_prefix;
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int add_score, del_score;
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/*
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* NEEDSWORK: this limits the recursion depth to hardcoded
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* value '2' to avoid excessive overhead.
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*/
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if (!depth_limit)
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depth_limit = 2;
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add_score = del_score = score_trees(hash1, hash2);
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add_prefix = xcalloc(1, 1);
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del_prefix = xcalloc(1, 1);
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/*
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* See if one's subtree resembles two; if so we need to prefix
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* two with a few fake trees to match the prefix.
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*/
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match_trees(hash1, hash2, &add_score, &add_prefix, "", depth_limit);
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/*
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* See if two's subtree resembles one; if so we need to
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* pick only subtree of two.
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*/
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match_trees(hash2, hash1, &del_score, &del_prefix, "", depth_limit);
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/* Assume we do not have to do any shifting */
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hashcpy(shifted, hash2);
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if (add_score < del_score) {
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/* We need to pick a subtree of two */
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unsigned mode;
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if (!*del_prefix)
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return;
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if (get_tree_entry(hash2, del_prefix, shifted, &mode))
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die("cannot find path %s in tree %s",
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del_prefix, sha1_to_hex(hash2));
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return;
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}
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if (!*add_prefix)
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return;
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splice_tree(hash1, add_prefix, hash2, shifted);
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}
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/*
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* The user says the trees will be shifted by this much.
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* Unfortunately we cannot fundamentally tell which one to
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* be prefixed, as recursive merge can work in either direction.
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*/
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void shift_tree_by(const unsigned char *hash1,
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const unsigned char *hash2,
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unsigned char *shifted,
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const char *shift_prefix)
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{
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unsigned char sub1[20], sub2[20];
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unsigned mode1, mode2;
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unsigned candidate = 0;
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/* Can hash2 be a tree at shift_prefix in tree hash1? */
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if (!get_tree_entry(hash1, shift_prefix, sub1, &mode1) &&
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S_ISDIR(mode1))
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candidate |= 1;
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/* Can hash1 be a tree at shift_prefix in tree hash2? */
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if (!get_tree_entry(hash2, shift_prefix, sub2, &mode2) &&
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S_ISDIR(mode2))
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candidate |= 2;
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if (candidate == 3) {
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/* Both are plausible -- we need to evaluate the score */
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int best_score = score_trees(hash1, hash2);
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int score;
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candidate = 0;
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score = score_trees(sub1, hash2);
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if (score > best_score) {
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candidate = 1;
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best_score = score;
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}
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score = score_trees(sub2, hash1);
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if (score > best_score)
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candidate = 2;
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}
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if (!candidate) {
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/* Neither is plausible -- do not shift */
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hashcpy(shifted, hash2);
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return;
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}
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if (candidate == 1)
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/*
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* shift tree2 down by adding shift_prefix above it
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* to match tree1.
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*/
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splice_tree(hash1, shift_prefix, hash2, shifted);
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else
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/*
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* shift tree2 up by removing shift_prefix from it
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* to match tree1.
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*/
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hashcpy(shifted, sub2);
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}
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