keep chunk's headers compatible at least up to LUAC_VERSION (to be

able to detect correctly version mismatches)

ldump.c

@@ -1,5 +1,5 @@
 /*
-** $Id: ldump.c,v 2.24 2014/03/01 15:18:44 roberto Exp roberto $
+** $Id: ldump.c,v 2.25 2014/03/10 17:56:32 roberto Exp roberto $
 ** save precompiled Lua chunks
 ** See Copyright Notice in lua.h
 */
@@ -160,11 +160,13 @@ static void DumpFunction (const Proto *f, DumpState *D) {
 }
 
 
+#define DumpLiteral(s,D)	DumpBlock(s, sizeof(s) - sizeof(char), D)
+
 static void DumpHeader (DumpState *D) {
-  DumpBlock(LUA_SIGNATURE, sizeof(LUA_SIGNATURE), D);
-  DumpBlock(LUAC_DATA, sizeof(LUAC_DATA), D);
+  DumpLiteral(LUA_SIGNATURE, D);
   DumpByte(LUAC_VERSION, D);
   DumpByte(LUAC_FORMAT, D);
+  DumpLiteral(LUAC_DATA, D);
   DumpByte(sizeof(int), D);
   DumpByte(sizeof(size_t), D);
   DumpByte(sizeof(Instruction), D);

lundump.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lundump.c,v 2.31 2014/03/10 17:56:32 roberto Exp roberto $
+** $Id: lundump.c,v 2.32 2014/03/10 19:50:19 roberto Exp roberto $
 ** load precompiled Lua chunks
 ** See Copyright Notice in lua.h
 */
@@ -195,10 +195,11 @@ static void LoadFunction (LoadState *S, Proto *f) {
 }
 
 
-static void checkstring (LoadState *S, const char *s, const char *msg) {
-  char buff[sizeof(LUA_SIGNATURE) + sizeof(LUAC_DATA)]; /* larger than each */
-  LoadVector(S, buff, strlen(s) + 1);
-  if (strcmp(s, buff) != 0)
+static void checkliteral (LoadState *S, const char *s, const char *msg) {
+  char buff[sizeof(LUA_SIGNATURE) + sizeof(LUAC_DATA)]; /* larger than both */
+  int len = strlen(s);
+  LoadVector(S, buff, len);
+  if (memcmp(s, buff, len) != 0)
     error(S, msg);
 }
 
@@ -212,12 +213,12 @@ static void fchecksize (LoadState *S, size_t size, const char *tname) {
 #define checksize(S,t)	fchecksize(S,sizeof(t),#t)
 
 static void checkHeader (LoadState *S) {
-  checkstring(S, LUA_SIGNATURE + 1, "not a");
-  checkstring(S, LUAC_DATA, "corrupted");
+  checkliteral(S, LUA_SIGNATURE + 1, "not a");  /* 1st char already checked */
   if (LoadByte(S) != LUAC_VERSION)
     error(S, "version mismatch in");
   if (LoadByte(S) != LUAC_FORMAT)
     error(S, "format mismatch in");
+  checkliteral(S, LUAC_DATA, "corrupted");
   checksize(S, int);
   checksize(S, size_t);
   checksize(S, Instruction);