Revising code for Varint encoding in dumps

- Usign lua_Unsigned to count strings.
- Varint uses a type large enough both for size_t and lua_Unsigned.
- Most-Significant Bit 0 means last byte, to conform to common usage.
- (unrelated) Change in macro 'getaddr' so that multiplication is
  by constants.

lundump.c

@@ -37,7 +37,7 @@ typedef struct {
   const char *name;
   Table *h;  /* list for string reuse */
   size_t offset;  /* current position relative to beginning of dump */
-  lua_Integer nstr;  /* number of strings in the list */
+  lua_Unsigned nstr;  /* number of strings in the list */
   lu_byte fixed;  /* dump is fixed in memory */
 } LoadState;
 
@@ -71,10 +71,9 @@ static void loadAlign (LoadState *S, int align) {
 }
 
 
-#define getaddr(S,n,t)	cast(t *, getaddr_(S,n,sizeof(t)))
+#define getaddr(S,n,t)	cast(t *, getaddr_(S,(n) * sizeof(t)))
 
-static const void *getaddr_ (LoadState *S, int n, size_t sz) {
-  size_t size = n * sz;
+static const void *getaddr_ (LoadState *S, size_t size) {
   const void *block = luaZ_getaddr(S->Z, size);
   S->offset += size;
   if (block == NULL)
@@ -95,8 +94,8 @@ static lu_byte loadByte (LoadState *S) {
 }
 
 
-static size_t loadUnsigned (LoadState *S, size_t limit) {
-  size_t x = 0;
+static varint_t loadVarint (LoadState *S, varint_t limit) {
+  varint_t x = 0;
   int b;
   limit >>= 7;
   do {
@@ -104,18 +103,18 @@ static size_t loadUnsigned (LoadState *S, size_t limit) {
     if (x >= limit)
       error(S, "integer overflow");
     x = (x << 7) | (b & 0x7f);
-  } while ((b & 0x80) == 0);
+  } while ((b & 0x80) != 0);
   return x;
 }
 
 
 static size_t loadSize (LoadState *S) {
-  return loadUnsigned(S, MAX_SIZET);
+  return cast_sizet(loadVarint(S, MAX_SIZET));
 }
 
 
 static int loadInt (LoadState *S) {
-  return cast_int(loadUnsigned(S, INT_MAX));
+  return cast_int(loadVarint(S, INT_MAX));
 }
 
 
@@ -149,9 +148,10 @@ static void loadString (LoadState *S, Proto *p, TString **sl) {
     return;
   }
   else if (size == 1) {  /* previously saved string? */
-    int idx = loadInt(S);  /* get its index */
+    /* get its index */
+    lua_Unsigned idx = cast(lua_Unsigned, loadVarint(S, LUA_MAXUNSIGNED));
     TValue stv;
-    luaH_getint(S->h, idx, &stv);
+    luaH_getint(S->h, l_castU2S(idx), &stv);  /* get its value */
     *sl = ts = tsvalue(&stv);
     luaC_objbarrier(L, p, ts);
     return;  /* do not save it again */
@@ -175,7 +175,7 @@ static void loadString (LoadState *S, Proto *p, TString **sl) {
   /* add string to list of saved strings */
   S->nstr++;
   setsvalue(L, &sv, ts);
-  luaH_setint(L, S->h, S->nstr, &sv);
+  luaH_setint(L, S->h, l_castU2S(S->nstr), &sv);
   luaC_objbarrierback(L, obj2gco(S->h), ts);
 }