Added suport for Fixed Buffers

A fixed buffer keeps a binary chunk "forever", so that the program
does not need to copy some of its parts when loading it.

lzio.c

@@ -45,17 +45,25 @@ void luaZ_init (lua_State *L, ZIO *z, lua_Reader reader, void *data) {
 
 
 /* --------------------------------------------------------------- read --- */
+
+static int checkbuffer (ZIO *z) {
+  if (z->n == 0) {  /* no bytes in buffer? */
+    if (luaZ_fill(z) == EOZ)  /* try to read more */
+      return 0;  /* no more input */
+    else {
+      z->n++;  /* luaZ_fill consumed first byte; put it back */
+      z->p--;
+    }
+  }
+  return 1;  /* now buffer has something */
+}
+
+
 size_t luaZ_read (ZIO *z, void *b, size_t n) {
   while (n) {
     size_t m;
-    if (z->n == 0) {  /* no bytes in buffer? */
-      if (luaZ_fill(z) == EOZ)  /* try to read more */
-        return n;  /* no more input; return number of missing bytes */
-      else {
-        z->n++;  /* luaZ_fill consumed first byte; put it back */
-        z->p--;
-      }
-    }
+    if (!checkbuffer(z))
+      return n;  /* no more input; return number of missing bytes */
     m = (n <= z->n) ? n : z->n;  /* min. between n and z->n */
     memcpy(b, z->p, m);
     z->n -= m;
@@ -66,3 +74,15 @@ size_t luaZ_read (ZIO *z, void *b, size_t n) {
   return 0;
 }
 
+
+const void *luaZ_getaddr (ZIO* z, size_t n) {
+  const void *res;
+  if (!checkbuffer(z))
+    return NULL;  /* no more input */
+  if (z->n < n)  /* not enough bytes? */
+    return NULL;  /* block not whole; cannot give an address */
+  res = z->p;  /* get block address */
+  z->n -= n;  /* consume these bytes */
+  z->p += n;
+  return res;
+}