The callee doesn't trust the high bits
A s16 or u8 argument still travels in a full 32-bit register — there's no half-size a0. The o32 rule is that the callee must not assume the upper bits are clean, so on arrival IDO re-extends every narrow argument itself. And narrow counts as "not a plain word", so — as you learned last lesson — narrow arguments get homed too. Two fingerprints for the price of one.
The re-extension differs by signedness. Here's narrowAdd(a, b) with both parameters declared s16:
sw a0, 0(sp) # narrow ⇒ homed
sll t6, a0, 16 # push the low half up…
sw a1, 4(sp) # (b homed too)
sll t8, a1, 16
sra a1, t8, 16 # …and arithmetic-shift back: sign bits refilled
sra a0, t6, 16
addu v0, a0, a1
jr ra
nop
The sll 16 / sra 16 pair is the signed narrow signature: shift the 16-bit value to the top, then shift back arithmetically so the sign bit smears down the upper half. For a signed byte it's the same dance with shift amount 24.
Unsigned narrows don't need the sign smear — a mask does the job: andi rt, rs, 255 for a u8, andi rt, rs, 65535 for a u16. Zero-extension in one instruction.
So narrow argument types read straight off the listing:
sll/sra by 16 → s16; by 24 → s8andi 65535 → u16; andi 255 → u8- plus a homing
sw for each narrow argument, interleaved by the scheduler
The target does one add. The mask and the homing tell you which argument is narrow, and what to declare.
Your task
Write func_802a00f8 to reproduce the target assembly.