fixed Bug #3051 "FLOOR returns invalid"

mysql-test/r/func_math.result:
  added test for Bug #3051 "FLOOR returns invalid"
mysql-test/t/func_math.test:
  added test for Bug #3051 "FLOOR returns invalid"

mysql-test/r/func_math.result

@@ -32,3 +32,9 @@ ASIN(0.8+0.2)
 1.570796
 ASIN(1.2-0.2)
 1.570796
+floor(log(4)/log(2))
+2
+floor(log(8)/log(2))
+3
+floor(log(16)/log(2))
+4

mysql-test/t/func_math.test

@@ -24,3 +24,11 @@ SELECT ACOS(0.2*5.0);
 SELECT ACOS(0.5*2.0);
 SELECT ASIN(0.8+0.2);
 SELECT ASIN(1.2-0.2);
+
+#
+# Bug #3051 FLOOR returns invalid 
+#
+
+select floor(log(4)/log(2));
+select floor(log(8)/log(2));
+select floor(log(16)/log(2));

sql/item_func.cc

@@ -572,7 +572,8 @@ longlong Item_func_ceiling::val_int()
 
 longlong Item_func_floor::val_int()
 {
-  double value=args[0]->val();
+  // the volatile's for BUG #3051 to calm optimizer down (because of gcc's bug)
+  volatile double value=args[0]->val();
   null_value=args[0]->null_value;
   return (longlong) floor(value);
 }