vcs-svn: implement perfect hash for node-prop keys

Instead of interning property names and comparing their string_pool
keys, look them up in a table by string length, which should be about
as fast.

This is a small step towards removing dependence on string_pool.

Signed-off-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>

vcs-svn/svndump.c

@@ -14,6 +14,12 @@
 #include "obj_pool.h"
 #include "string_pool.h"
 
+/*
+ * Compare start of string to literal of equal length;
+ * must be guarded by length test.
+ */
+#define constcmp(s, ref) memcmp(s, ref, sizeof(ref) - 1)
+
 #define NODEACT_REPLACE 4
 #define NODEACT_DELETE 3
 #define NODEACT_ADD 2
@@ -58,8 +64,7 @@ static struct {
 } dump_ctx;
 
 static struct {
-	uint32_t svn_log, svn_author, svn_date, svn_executable, svn_special, uuid,
+	uint32_t uuid, revision_number, node_path, node_kind, node_action,
-		revision_number, node_path, node_kind, node_action,
 		node_copyfrom_path, node_copyfrom_rev, text_content_length,
 		prop_content_length, content_length, svn_fs_dump_format_version,
 		/* version 3 format */
@@ -96,11 +101,6 @@ static void reset_dump_ctx(uint32_t url)
 
 static void init_keys(void)
 {
-	keys.svn_log = pool_intern("svn:log");
-	keys.svn_author = pool_intern("svn:author");
-	keys.svn_date = pool_intern("svn:date");
-	keys.svn_executable = pool_intern("svn:executable");
-	keys.svn_special = pool_intern("svn:special");
 	keys.uuid = pool_intern("UUID");
 	keys.revision_number = pool_intern("Revision-number");
 	keys.node_path = pool_intern("Node-path");
@@ -117,22 +117,43 @@ static void init_keys(void)
 	keys.prop_delta = pool_intern("Prop-delta");
 }
 
-static void handle_property(uint32_t key, const char *val, uint32_t len,
+static void handle_property(const struct strbuf *key_buf,
+				const char *val, uint32_t len,
 				uint32_t *type_set)
 {
-	if (key == keys.svn_log) {
+	const char *key = key_buf->buf;
+	size_t keylen = key_buf->len;
+
+	switch (keylen + 1) {
+	case sizeof("svn:log"):
+		if (constcmp(key, "svn:log"))
+			break;
 		if (!val)
 			die("invalid dump: unsets svn:log");
 		/* Value length excludes terminating nul. */
 		rev_ctx.log = log_copy(len + 1, val);
-	} else if (key == keys.svn_author) {
+		break;
+	case sizeof("svn:author"):
+		if (constcmp(key, "svn:author"))
+			break;
 		rev_ctx.author = pool_intern(val);
-	} else if (key == keys.svn_date) {
+		break;
+	case sizeof("svn:date"):
+		if (constcmp(key, "svn:date"))
+			break;
 		if (!val)
 			die("invalid dump: unsets svn:date");
 		if (parse_date_basic(val, &rev_ctx.timestamp, NULL))
 			warning("invalid timestamp: %s", val);
-	} else if (key == keys.svn_executable || key == keys.svn_special) {
+		break;
+	case sizeof("svn:executable"):
+	case sizeof("svn:special"):
+		if (keylen == strlen("svn:executable") &&
+		    constcmp(key, "svn:executable"))
+			break;
+		if (keylen == strlen("svn:special") &&
+		    constcmp(key, "svn:special"))
+			break;
 		if (*type_set) {
 			if (!val)
 				return;
@@ -143,7 +164,7 @@ static void handle_property(uint32_t key, const char *val, uint32_t len,
 			return;
 		}
 		*type_set = 1;
-		node_ctx.type = key == keys.svn_executable ?
+		node_ctx.type = keylen == strlen("svn:executable") ?
 				REPO_MODE_EXE :
 				REPO_MODE_LNK;
 	}
@@ -158,7 +179,7 @@ static void die_short_read(void)
 
 static void read_props(void)
 {
-	uint32_t key = ~0;
+	static struct strbuf key = STRBUF_INIT;
 	const char *t;
 	/*
 	 * NEEDSWORK: to support simple mode changes like
@@ -195,16 +216,19 @@ static void read_props(void)
 
 		switch (type) {
 		case 'K':
-			key = pool_intern(val);
-			continue;
 		case 'D':
-			key = pool_intern(val);
+			strbuf_reset(&key);
+			if (val)
+				strbuf_add(&key, val, len);
+			if (type == 'K')
+				continue;
+			assert(type == 'D');
 			val = NULL;
 			len = 0;
 			/* fall through */
 		case 'V':
-			handle_property(key, val, len, &type_set);
+			handle_property(&key, val, len, &type_set);
-			key = ~0;
+			strbuf_reset(&key);
 			continue;
 		default:
 			die("invalid property line: %s\n", t);