The Insert a Variable Bit Field routine replaces the variable bit
    field specified by the base, position, and size arguments with
    bits 0 through (size-1) of the source field. If the size of the
    bit field is zero, nothing is inserted. LIB$INSV makes the VAX
    INSV instruction available as a callable routine.

    Format

      LIB$INSV  longword-integer-source ,position ,size ,base-address