Memcache::decrement() decrements value of the item by value. Similarly to Memcache::increment(), current value of the item is being converted to numerical and after that value is substracted.
Parameter value is optional. It's default is 1.
Note: New item's value will not be less than zero.
Note: Do not use Memcache::decrement() with item, which was stored compressed, because consequent call to Memcache::get() will fail.
Also you can use memcache_decrement() function. See example below.
Memcache::decrement() does not create an item if it didn't exist.
Memcache::decrement() returns item's new value on success or FALSE on failure.
See also Memcache::increment(), Memcache::replace().