lua

commit 25cd3d377ec13176a6701d9d21a278ba8f2bc3d6
parent 1028f296a8e6477cb556c75fe1397cd4e2762abe
Author: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date:   Wed, 15 Nov 2023 10:28:05 -0300

Buffer in 'luai_makeseed' measured in bytes

In the (rare) cases when sizeof(void*) or sizeof(time_t) are not
multiples of sizeof(int), we still can use all their bytes in the seed.

Diffstat:
M
lauxlib.c
 | 
25
+++++++++++++------------
M
ltests.c
 | 
7
+++++++

2 files changed, 20 insertions(+), 12 deletions(-)
diff --git a/lauxlib.c b/lauxlib.c
@@ -1124,29 +1124,30 @@ static void warnfon (void *ud, const char *message, int tocont) {
 #include <time.h>
 
 
-/*
-** Size of 'e' measured in number of 'unsigned int's. (In the weird
-** case that the division truncates, we just lose some part of the
-** value, no big deal.)
-*/
-#define sof(e)          (sizeof(e) / sizeof(unsigned int))
+/* Size for the buffer, in bytes */
+#define BUFSEEDB	(sizeof(void*) + sizeof(time_t))
+
+/* Size for the buffer in int's, rounded up */
+#define BUFSEED		((BUFSEEDB + sizeof(int) - 1) / sizeof(int))
 
 
-#define addbuff(b,v) \
-	(memcpy(b, &(v), sof(v) * sizeof(unsigned int)), b += sof(v))
+#define addbuff(b,v)	(memcpy(b, &(v), sizeof(v)), b += sizeof(v))
 
 
 static unsigned int luai_makeseed (void) {
-  unsigned int buff[sof(void*) + sof(time_t)];
+  unsigned int buff[BUFSEED];
   unsigned int res;
-  unsigned int *b = buff;
+  unsigned int i;
   time_t t = time(NULL);
   void *h = buff;
+  char *b = (char*)buff;
   addbuff(b, h);  /* local variable's address */
   addbuff(b, t);  /* time */
+  /* fill (rare but possible) remain of the buffer with zeros */
+  memset(b, 0, BUFSEED * sizeof(int) - BUFSEEDB);
   res = buff[0];
-  for (b = buff + 1; b < buff + sof(buff); b++)
-    res ^= (res >> 3) + (res << 7) + *b;
+  for (i = 0; i < BUFSEED; i++)
+    res ^= (res >> 3) + (res << 7) + buff[i];
   return res;
 }
 
diff --git a/ltests.c b/ltests.c
@@ -1160,6 +1160,12 @@ static int num2int (lua_State *L) {
 }
 
 
+static int makeseed (lua_State *L) {
+  lua_pushinteger(L, luaL_makeseed(L));
+  return 1;
+}
+
+
 static int newstate (lua_State *L) {
   void *ud;
   lua_Alloc f = lua_getallocf(L, &ud);
@@ -1962,6 +1968,7 @@ static const struct luaL_Reg tests_funcs[] = {
   {"newstate", newstate},
   {"newuserdata", newuserdata},
   {"num2int", num2int},
+  {"makeseed", makeseed},
   {"pushuserdata", pushuserdata},
   {"querystr", string_query},
   {"querytab", table_query},