db: smarter string pointer encoding (include length field)

So we don't need explicit null terminator in most cases saving
space. It will also speed up comparisons as getting string blob is
now constant time (no strlen needed).

1 files changed, 14 insertions, 7 deletions

diff --git a/lua-squarkdb.c b/lua-squarkdb.c
index dbac6d0..09d4afe 100644
--- a/lua-squarkdb.c
+++ b/lua-squarkdb.c
@@ -227,7 +227,7 @@ static int Lsqdb_map_strings(lua_State *L)
 {
 	struct sqdb *db;
 	const char *str;
-	char *ptr;
+	unsigned char *ptr;
 	size_t len, total, pos;
 
 	db = Lsqdb_checkarg(L, 1);
@@ -238,7 +238,9 @@ static int Lsqdb_map_strings(lua_State *L)
 	lua_pushnil(L);
 	while (lua_next(L, 2) != 0) {
 		str = luaL_checklstring(L, -2, &len);
-		total += len + 1;
+		total += len;
+		if (len >= (1 << SQDB_LENGTH_BITS))
+			total++;
 		lua_pop(L, 1);
 	}
 
@@ -252,15 +254,20 @@ static int Lsqdb_map_strings(lua_State *L)
 	lua_pushnil(L);
 	while (lua_next(L, 2) != 0) {
 		str = lua_tolstring(L, -2, &len);
-		memcpy(&ptr[pos], str, len + 1);
 		lua_pop(L, 1);
 
-		/* table[key] = pos */
+		/* table[key] = encoded_string_pointer */
 		lua_pushvalue(L, -1);
-		lua_pushinteger(L, pos);
-		lua_rawset(L, 2);
+		if (len >= (1 << SQDB_LENGTH_BITS)) {
+			lua_pushinteger(L, pos << SQDB_LENGTH_BITS);
+			ptr[pos++] = len;
+		} else {
+			lua_pushinteger(L, (pos << SQDB_LENGTH_BITS) + len);
+		}
+		memcpy(&ptr[pos], str, len);
+		pos += len;
 
-		pos += len + 1;
+		lua_rawset(L, 2);
 	}
 
 	return 0;