Generates
bit masks for elements in the return vector. For each halfword element
in
d, a bit mask is generated. The mask consists
of bits set to one starting at the bit position specified by
a and
ending with the bit position specified by
b. All
other bit positions are set to zero.
Notes: - If a or b is greater than 16,
the operation is performed as if the value gets modulo by 16.
- If a is greater than b, the
operation is perform as if b equals 15.