describe: Store commit_names in a hash table by commit SHA1

describe is currently forced to look up the commit at each tag in
order to store the struct commit_name pointers in struct commit.util.
For --exact-match queries, those lookups are wasteful.  In preparation
for removing them, put the commit_names into a hash table, indexed by
commit SHA1, that can be used to quickly check for exact matches.

Signed-off-by: Anders Kaseorg <andersk@ksplice.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/describe.c b/builtin/describe.c
index 5b8461d87fa03eb9ec2363c2bea0bfa1126c57cc..8149233059d84155cb3d2385e1bc19042f539b6c 100644 (file)
--- a/builtin/describe.c
+++ b/builtin/describe.c
@@ -6,6 +6,7 @@
 #include "exec_cmd.h"
 #include "parse-options.h"
 #include "diff.h"
+#include "hash.h"
 
 #define SEEN           (1u<<0)
 #define MAX_TAGS       (FLAG_BITS - 1)
@@ -22,7 +23,7 @@ static int tags;      /* Allow lightweight tags */
 static int longformat;
 static int abbrev = DEFAULT_ABBREV;
 static int max_candidates = 10;
-static int found_names;
+static struct hash_table names;
 static const char *pattern;
 static int always;
 static const char *dirty;
@@ -34,6 +35,8 @@ static const char *diff_index_args[] = {
 
 
 struct commit_name {
+       struct commit_name *next;
+       unsigned char peeled[20];
        struct tag *tag;
        unsigned prio:2; /* annotated tag = 2, tag = 1, head = 0 */
        unsigned name_checked:1;
@@ -44,6 +47,21 @@ static const char *prio_names[] = {
        "head", "lightweight", "annotated",
 };
 
+static inline unsigned int hash_sha1(const unsigned char *sha1)
+{
+       unsigned int hash;
+       memcpy(&hash, sha1, sizeof(hash));
+       return hash;
+}
+
+static inline struct commit_name *find_commit_name(const unsigned char *peeled)
+{
+       struct commit_name *n = lookup_hash(hash_sha1(peeled), &names);
+       while (n && !!hashcmp(peeled, n->peeled))
+               n = n->next;
+       return n;
+}
+
 static int replace_name(struct commit_name *e,
                               int prio,
                               const unsigned char *sha1,
@@ -82,12 +100,22 @@ static void add_to_known_names(const char *path,
                               int prio,
                               const unsigned char *sha1)
 {
-       struct commit_name *e = commit->util;
+       const unsigned char *peeled = commit->object.sha1;
+       struct commit_name *e = find_commit_name(peeled);
        struct tag *tag = NULL;
        if (replace_name(e, prio, sha1, &tag)) {
                if (!e) {
+                       void **pos;
                        e = xmalloc(sizeof(struct commit_name));
                        commit->util = e;
+                       hashcpy(e->peeled, peeled);
+                       pos = insert_hash(hash_sha1(peeled), e, &names);
+                       if (pos) {
+                               e->next = *pos;
+                               *pos = e;
+                       } else {
+                               e->next = NULL;
+                       }
                }
                e->tag = tag;
                e->prio = prio;
@@ -95,7 +123,6 @@ static void add_to_known_names(const char *path,
                hashcpy(e->sha1, sha1);
                e->path = path;
        }
-       found_names = 1;
 }
 
 static int get_name(const char *path, const unsigned char *sha1, int flag, void *cb_data)
@@ -240,7 +267,7 @@ static void describe(const char *arg, int last_one)
        if (!cmit)
                die("%s is not a valid '%s' object", arg, commit_type);
 
-       n = cmit->util;
+       n = find_commit_name(cmit->object.sha1);
        if (n && (tags || all || n->prio == 2)) {
                /*
                 * Exact match to an existing ref.
@@ -418,8 +445,9 @@ int cmd_describe(int argc, const char **argv, const char *prefix)
                return cmd_name_rev(i + argc, args, prefix);
        }
 
+       init_hash(&names);
        for_each_rawref(get_name, NULL);
-       if (!found_names && !always)
+       if (!names.nr && !always)
                die("No names found, cannot describe anything.");
 
        if (argc == 0) {