Before the patch, SingleInteger was also choosen as representation
for IntegerMod(p) if p was in the range m/2 < p <= m := max()$SingleInteger.
(1) -> I ==> SingleInteger
(2) -> p: I := max()$I - 123456
(2) 4611686018427264447
Type: SingleInteger
(3) -> a: I := p - 1
(3) 4611686018427264446
Type: SingleInteger
(4) -> a + a
>> System error:
The value
9223372036854528892
is not of type
FIXNUM
(4) -> addmod(a, a, p)
>> System error:
The value
9223372036854528892
is not of type
FIXNUM