bitfromint4() in v7.2.3 to bit() in v8.1?

select substring(bitfromint4(cast (-2^31 + 22 as int4)), 1, 32);

and now I'm porting the legacy code, that this line is part of, to version 8.1 but am having no luck updating it - have tried something like:

select substring(bit(cast (-2^31 + 22 as int4)), 1, 32);

and

select substring("bit"(cast (-2^31 + 22 as int4)), 1, 32);

and

select substring(1::"bit"(cast (-2^31 + 22 as int4)), 1, 32);

with no luck.

How can this be solved?

/Björn