Merge branch 'jh/add-index-entry-optim'
[git/git.git] / read-cache.c
index 008b335..d8c657d 100644 (file)
@@ -887,9 +887,32 @@ static int has_file_name(struct index_state *istate,
        return retval;
 }
 
+
+/*
+ * Like strcmp(), but also return the offset of the first change.
+ * If strings are equal, return the length.
+ */
+int strcmp_offset(const char *s1, const char *s2, size_t *first_change)
+{
+       size_t k;
+
+       if (!first_change)
+               return strcmp(s1, s2);
+
+       for (k = 0; s1[k] == s2[k]; k++)
+               if (s1[k] == '\0')
+                       break;
+
+       *first_change = k;
+       return (unsigned char)s1[k] - (unsigned char)s2[k];
+}
+
 /*
  * Do we have another file with a pathname that is a proper
  * subset of the name we're trying to add?
+ *
+ * That is, is there another file in the index with a path
+ * that matches a sub-directory in the given entry?
  */
 static int has_dir_name(struct index_state *istate,
                        const struct cache_entry *ce, int pos, int ok_to_replace)
@@ -898,9 +921,51 @@ static int has_dir_name(struct index_state *istate,
        int stage = ce_stage(ce);
        const char *name = ce->name;
        const char *slash = name + ce_namelen(ce);
+       size_t len_eq_last;
+       int cmp_last = 0;
+
+       /*
+        * We are frequently called during an iteration on a sorted
+        * list of pathnames and while building a new index.  Therefore,
+        * there is a high probability that this entry will eventually
+        * be appended to the index, rather than inserted in the middle.
+        * If we can confirm that, we can avoid binary searches on the
+        * components of the pathname.
+        *
+        * Compare the entry's full path with the last path in the index.
+        */
+       if (istate->cache_nr > 0) {
+               cmp_last = strcmp_offset(name,
+                       istate->cache[istate->cache_nr - 1]->name,
+                       &len_eq_last);
+               if (cmp_last > 0) {
+                       if (len_eq_last == 0) {
+                               /*
+                                * The entry sorts AFTER the last one in the
+                                * index and their paths have no common prefix,
+                                * so there cannot be a F/D conflict.
+                                */
+                               return retval;
+                       } else {
+                               /*
+                                * The entry sorts AFTER the last one in the
+                                * index, but has a common prefix.  Fall through
+                                * to the loop below to disect the entry's path
+                                * and see where the difference is.
+                                */
+                       }
+               } else if (cmp_last == 0) {
+                       /*
+                        * The entry exactly matches the last one in the
+                        * index, but because of multiple stage and CE_REMOVE
+                        * items, we fall through and let the regular search
+                        * code handle it.
+                        */
+               }
+       }
 
        for (;;) {
-               int len;
+               size_t len;
 
                for (;;) {
                        if (*--slash == '/')
@@ -910,6 +975,67 @@ static int has_dir_name(struct index_state *istate,
                }
                len = slash - name;
 
+               if (cmp_last > 0) {
+                       /*
+                        * (len + 1) is a directory boundary (including
+                        * the trailing slash).  And since the loop is
+                        * decrementing "slash", the first iteration is
+                        * the longest directory prefix; subsequent
+                        * iterations consider parent directories.
+                        */
+
+                       if (len + 1 <= len_eq_last) {
+                               /*
+                                * The directory prefix (including the trailing
+                                * slash) also appears as a prefix in the last
+                                * entry, so the remainder cannot collide (because
+                                * strcmp said the whole path was greater).
+                                *
+                                * EQ: last: xxx/A
+                                *     this: xxx/B
+                                *
+                                * LT: last: xxx/file_A
+                                *     this: xxx/file_B
+                                */
+                               return retval;
+                       }
+
+                       if (len > len_eq_last) {
+                               /*
+                                * This part of the directory prefix (excluding
+                                * the trailing slash) is longer than the known
+                                * equal portions, so this sub-directory cannot
+                                * collide with a file.
+                                *
+                                * GT: last: xxxA
+                                *     this: xxxB/file
+                                */
+                               return retval;
+                       }
+
+                       if (istate->cache_nr > 0 &&
+                               ce_namelen(istate->cache[istate->cache_nr - 1]) > len) {
+                               /*
+                                * The directory prefix lines up with part of
+                                * a longer file or directory name, but sorts
+                                * after it, so this sub-directory cannot
+                                * collide with a file.
+                                *
+                                * last: xxx/yy-file (because '-' sorts before '/')
+                                * this: xxx/yy/abc
+                                */
+                               return retval;
+                       }
+
+                       /*
+                        * This is a possible collision. Fall through and
+                        * let the regular search code handle it.
+                        *
+                        * last: xxx
+                        * this: xxx/file
+                        */
+               }
+
                pos = index_name_stage_pos(istate, name, len, stage);
                if (pos >= 0) {
                        /*
@@ -1001,7 +1127,16 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e
 
        if (!(option & ADD_CACHE_KEEP_CACHE_TREE))
                cache_tree_invalidate_path(istate, ce->name);
-       pos = index_name_stage_pos(istate, ce->name, ce_namelen(ce), ce_stage(ce));
+
+       /*
+        * If this entry's path sorts after the last entry in the index,
+        * we can avoid searching for it.
+        */
+       if (istate->cache_nr > 0 &&
+               strcmp(ce->name, istate->cache[istate->cache_nr - 1]->name) > 0)
+               pos = -istate->cache_nr - 1;
+       else
+               pos = index_name_stage_pos(istate, ce->name, ce_namelen(ce), ce_stage(ce));
 
        /* existing match? Just replace it. */
        if (pos >= 0) {