Two arms, one join
The ternary ?: produces a shape you'll learn to spot from across the room. Here's return x ? a : b;:
0: beqz a0, 0x10 # x == 0? the else-arm
4: or v1, a2, zero # (delay slot) v1 = b — the else value
8: b 0x10 # unconditional hop to the join
c: or v1, a1, zero # (delay slot) v1 = a — the then value
10: or v0, v1, zero # the join: whichever arm ran, copy to v0
14: jr ra
18: nop
Three things make this a diamond, not a ladder:
- Both arms write the same scratch register. Each path deposits its value in
v1, and a single join line moves v1 into v0. That arm-arm-join flow through an intermediate register is the ternary's signature — early returns (a ladder) would each have their own jr ra instead.
b is the unconditional branch. No condition, always taken — it exists purely to jump the then-arm over the join point's fall-in. And yes, it has a delay slot like any branch; here the slot is the then-arm.- Each arm lives in a slot. The else-value under the
beqz, the then-value under the b. Four instructions of logic, two of them in shadows — if you only read non-slot lines, this function looks empty.
Decode order: condition off the branch (flipped — beqz means the x == 0 case goes to the else value), then each arm's expression out of its slot. One line of C.
In the target, the arms aren't bare copies — each one computes something with the same two values before it lands in v1. Same diamond, one operation per arm.
Your task
Write func_8003b1d0 to reproduce the target assembly.