The function checks whether dict contains key. If it isn't so then the function checks the datatype of the value associated with the key. An error 42000 is signalled in case of non-integer value or a negative integer value. If the value is positive and greater than value_decrement then value_decrement is subtracted from it and the result become the new value associated with key in dict. If the value is positive and less than or equal to value_decrement then key is removed from dict. If key is not in the dictionary then the dictionary remains unchanged.
Informally, the function reverts the effect of dict_inc_or_add.
The function returns the changed value associated with the key, or zero in any other case.