Postgresql - Logical casts Int4 to/from Int8

logical-casts-int4-int8.pg

int4_bits_from_int8 := (WITH ValueAndShiftRight(int8_bits, shiftRight) AS ( 
    SELECT -8187830383155378919::bigint, 32
)
SELECT
    (CASE (int8_bits::bit(64) >> shiftRight)::bigint & (1::bigint << 31)
        WHEN 0 THEN ((int8_bits::bit(64) >> shiftRight) & x'FFFFFFFF'::bigint::bit(64))::bigint
        ELSE ~((~((int8_bits::bit(64) >> shiftRight))::bigint & x'FFFFFFFF'::bigint)::int) END)::int
FROM ValueAndShiftRight);

int8_bits_from_int4 := (WITH ValueAndShiftLeft(int4_bits, shiftLeft) AS ( 
    SELECT -11::int, 31
)
SELECT
    CASE 
        WHEN 0 <= int4_bits THEN int4_bits::bigint << shiftLeft
        ELSE (~((~int4_bits)::bigint) & x'FFFFFFFF'::bigint) << shiftLeft END
FROM ValueAndShiftLeft);