[PATCH 18/27] [GSOC] ref-filter: use atom_type and merge two for loop in grab_person

["ZheNing Hu via GitGitGadget" <gitgitgadget@gmail.com>]

From: ZheNing Hu <adlternative@gmail.com>

grab_person() uses string for atom type comparison, this is very
inefficient, we can use atom_type to replace it. At the same time,
we can merge the two for loops in grab_person() into one, this can
reduce unnecessary traversal of the used_atom list.

With this patch, `git cat-file --batch` has a 2% performance
improvement.

Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Hariom Verma <hariom18599@gmail.com>
Signed-off-by: ZheNing Hu <adlternative@gmail.com>
---
 ref-filter.c | 57 +++++++++++++++++-----------------------------------
 1 file changed, 18 insertions(+), 39 deletions(-)

diff --git a/ref-filter.c b/ref-filter.c
index 1251e062ff8..3ccb531e073 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -1307,63 +1307,42 @@ static void grab_date(const char *buf, struct atom_value *v, const char *atomnam
 }
 
 /* See grab_values */
-static void grab_person(const char *who, struct atom_value *val, int deref, void *buf)
+static void grab_person(enum atom_type type, struct atom_value *val, int deref, void *buf)
 {
 	int i;
+	const char *who = valid_atom[type].name;
 	int wholen = strlen(who);
 	const char *wholine = NULL;
 
 	for (i = 0; i < used_atom_cnt; i++) {
 		const char *name = used_atom[i].name;
+		enum atom_type atom_type = used_atom[i].atom_type;
 		struct atom_value *v = &val[i];
 		if (!!deref != (*name == '*'))
 			continue;
 		if (deref)
 			name++;
-		if (strncmp(who, name, wholen))
-			continue;
-		if (name[wholen] != 0 &&
-		    strcmp(name + wholen, "name") &&
-		    !starts_with(name + wholen, "email") &&
-		    !starts_with(name + wholen, "date"))
+		if ((atom_type < type || atom_type > type + 3) &&
+		    /*
+		    * For a tag or a commit object, if "creator" or "creatordate" is
+		    * requested, do something special.
+		    */
+		    ((atom_type != ATOM_CREATOR && atom_type != ATOM_CREATORDATE) ||
+		     ((atom_type == ATOM_CREATOR || atom_type == ATOM_CREATORDATE) &&
+		      type != ATOM_TAGGER && type != ATOM_COMMITTER)))
 			continue;
 		if (!wholine)
 			wholine = find_wholine(who, wholen, buf);
 		if (!wholine)
 			return; /* no point looking for it */
-		if (name[wholen] == 0)
+		if (atom_type == type || atom_type == ATOM_CREATOR)
 			v->s = copy_line(wholine);
-		else if (!strcmp(name + wholen, "name"))
+		else if (atom_type == type + 1)
 			v->s = copy_name(wholine);
-		else if (starts_with(name + wholen, "email"))
+		else if (atom_type == type + 2)
 			v->s = copy_email(wholine, &used_atom[i]);
-		else if (starts_with(name + wholen, "date"))
-			grab_date(wholine, v, name);
-	}
-
-	/*
-	 * For a tag or a commit object, if "creator" or "creatordate" is
-	 * requested, do something special.
-	 */
-	if (strcmp(who, "tagger") && strcmp(who, "committer"))
-		return; /* "author" for commit object is not wanted */
-	if (!wholine)
-		wholine = find_wholine(who, wholen, buf);
-	if (!wholine)
-		return;
-	for (i = 0; i < used_atom_cnt; i++) {
-		const char *name = used_atom[i].name;
-		enum atom_type atom_type = used_atom[i].atom_type;
-		struct atom_value *v = &val[i];
-		if (!!deref != (*name == '*'))
-			continue;
-		if (deref)
-			name++;
-
-		if (atom_type == ATOM_CREATORDATE)
+		else if (atom_type == type + 3 || atom_type == ATOM_CREATORDATE)
 			grab_date(wholine, v, name);
-		else if (atom_type == ATOM_CREATOR)
-			v->s = copy_line(wholine);
 	}
 }
 
@@ -1553,14 +1532,14 @@ static void grab_values(struct atom_value *val, int deref, struct object *obj, s
 		if (obj)
 			grab_tag_values(val, deref, obj);
 		grab_sub_body_contents(val, deref, data);
-		grab_person("tagger", val, deref, buf);
+		grab_person(ATOM_TAGGER, val, deref, buf);
 		break;
 	case OBJ_COMMIT:
 		if (obj)
 			grab_commit_values(val, deref, obj);
 		grab_sub_body_contents(val, deref, data);
-		grab_person("author", val, deref, buf);
-		grab_person("committer", val, deref, buf);
+		grab_person(ATOM_AUTHOR, val, deref, buf);
+		grab_person(ATOM_COMMITTER, val, deref, buf);
 		break;
 	case OBJ_TREE:
 		/* grab_tree_values(val, deref, obj, buf, sz); */
-- 
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