Catalyzes the hydrolysis of alpha-1,4 glycosidic linkages in starch, glycogen and similar oligosaccharides. Endohydrolysis of (1->4)-alpha-D-glucosidic linkages in polysaccharides containing three or more (1->4)-alpha-linked D-glucose units. Binds 1 Ca(2+) ion per subunit. Binds 1 Cl(-) ion per subunit. Optimum pH is 7.1. Optimum temperature is 50 degrees Celsius. Belongs to the glycosyl hydrolase 13 family.