util.strbitop: Create buffer in the correct size (optimization)

This avoids dynamically growing the buffer as Lua does when luaL_addchar
is used, thus saving on realloc calls.

1 files changed, 13 insertions, 6 deletions

diff --git a/util-src/strbitop.c b/util-src/strbitop.c
index 89fce661..922048fd 100644
--- a/util-src/strbitop.c
+++ b/util-src/strbitop.c
@@ -2,7 +2,7 @@
  * This project is MIT licensed. Please see the
  * COPYING file in the source package for more information.
  *
- * Copyright (C) 2016 Kim Alvefur
+ * Copyright (C) 2016-2020 Kim Alvefur
  */
 
 #include <lua.h>
@@ -27,10 +27,13 @@ int strop_and(lua_State *L) {
 		return 1;
 	}
 
+	char *cbuf = luaL_buffinitsize(L, &buf, a);
+
 	for(i = 0; i < a; i++) {
-		luaL_addchar(&buf, str_a[i] & str_b[i % b]);
+		cbuf[i] = str_a[i] & str_b[i % b];
 	}
 
+	luaL_addsize(&buf, a);
 	luaL_pushresult(&buf);
 	return 1;
 }
@@ -48,10 +51,13 @@ int strop_or(lua_State *L) {
 		return 1;
 	}
 
+	char *cbuf = luaL_buffinitsize(L, &buf, a);
+
 	for(i = 0; i < a; i++) {
-		luaL_addchar(&buf, str_a[i] | str_b[i % b]);
+		cbuf[i] = str_a[i] | str_b[i % b];
 	}
 
+	luaL_addsize(&buf, a);
 	luaL_pushresult(&buf);
 	return 1;
 }
@@ -62,17 +68,18 @@ int strop_xor(lua_State *L) {
 	const char *str_a = luaL_checklstring(L, 1, &a);
 	const char *str_b = luaL_checklstring(L, 2, &b);
 
-	luaL_buffinit(L, &buf);
-
 	if(a == 0 || b == 0) {
 		lua_settop(L, 1);
 		return 1;
 	}
 
+	char *cbuf = luaL_buffinitsize(L, &buf, a);
+
 	for(i = 0; i < a; i++) {
-		luaL_addchar(&buf, str_a[i] ^ str_b[i % b]);
+		cbuf[i] = str_a[i] ^ str_b[i % b];
 	}
 
+	luaL_addsize(&buf, a);
 	luaL_pushresult(&buf);
 	return 1;
 }