variable.c: resurrect `size` member in `iv_tbl`.

The existence of this member reduces memory and execution time.

src/variable.c

@@ -14,7 +14,7 @@
 
 /* Instance variable table structure */
 typedef struct iv_tbl {
-  size_t alloc;
+  size_t size, alloc;
   mrb_value *ptr;
 } iv_tbl;
 
@@ -47,6 +47,7 @@ iv_rehash(mrb_state *mrb, iv_tbl *t)
   khash_power2(new_alloc);
   if (old_alloc == new_alloc) return;
 
+  t->size = 0;
   t->alloc = new_alloc;
   t->ptr = (mrb_value*)mrb_calloc(mrb, sizeof(mrb_value)+sizeof(mrb_sym), new_alloc);
   if (old_alloc == 0) return;
@@ -84,6 +85,7 @@ iv_put(mrb_state *mrb, iv_tbl *t, mrb_sym sym, mrb_value val)
       return;
     }
     else if (key == IV_EMPTY) {
+      t->size++;
       keys[pos] = sym;
       vals[pos] = val;
       return;
@@ -94,6 +96,7 @@ iv_put(mrb_state *mrb, iv_tbl *t, mrb_sym sym, mrb_value val)
     pos = (pos+1) & (t->alloc-1);
     if (pos == start) {         /* not found */
       if (dpos >= 0) {
+        t->size++;
         keys[dpos] = sym;
         vals[dpos] = val;
         return;
@@ -115,6 +118,7 @@ iv_get(mrb_state *mrb, iv_tbl *t, mrb_sym sym, mrb_value *vp)
 
   if (t == NULL) return FALSE;
   if (t->alloc == 0) return FALSE;
+  if (t->size == 0) return FALSE;
 
   mrb_sym *keys = (mrb_sym*)&t->ptr[t->alloc];
   mrb_value *vals = t->ptr;
@@ -143,7 +147,8 @@ iv_del(mrb_state *mrb, iv_tbl *t, mrb_sym sym, mrb_value *vp)
   size_t hash, pos, start;
 
   if (t == NULL) return FALSE;
-  if (t->alloc == 0) return  FALSE;
+  if (t->alloc == 0) return FALSE;
+  if (t->size == 0) return FALSE;
 
   mrb_sym *keys = (mrb_sym*)&t->ptr[t->alloc];
   mrb_value *vals = t->ptr;
@@ -153,6 +158,7 @@ iv_del(mrb_state *mrb, iv_tbl *t, mrb_sym sym, mrb_value *vp)
     mrb_sym key = keys[pos];
     if (key == sym) {
       if (vp) *vp = vals[pos];
+      t->size--;
       keys[pos] = IV_DELETED;
       return TRUE;
     }
@@ -174,6 +180,7 @@ iv_foreach(mrb_state *mrb, iv_tbl *t, mrb_iv_foreach_func *func, void *p)
 
   if (t == NULL) return;
   if (t->alloc == 0) return;
+  if (t->size == 0) return;
 
   mrb_sym *keys = (mrb_sym*)&t->ptr[t->alloc];
   mrb_value *vals = t->ptr;
@@ -193,7 +200,7 @@ static size_t
 iv_size(mrb_state *mrb, iv_tbl *t)
 {
   if (t == NULL) return 0;
-  return t->alloc;
+  return t->size;
 }
 
 /* Copy the instance variable table. */
@@ -205,6 +212,7 @@ iv_copy(mrb_state *mrb, iv_tbl *t)
 
   if (t == NULL) return NULL;
   if (t->alloc == 0) return NULL;
+  if (t->size == 0) return NULL;
 
   mrb_sym *keys = (mrb_sym*)&t->ptr[t->alloc];
   mrb_value *vals = t->ptr;