Three writes, no conversions
Structs are next chapter's business, but game code packs bytes into buffers with plain pointers all the time — message headers, color triplets, tile attributes. The shape is a run of sbs at stepping offsets, and the pleasure of it is everything that isn't there. Here's set_header, which writes a kind byte and clears the byte after it:
void set_header(u8 *h, s32 kind) {
h[0] = kind;
h[1] = 0;
}
sb a1, 0(a0) # h[0] = kind — sb truncates for free
sb zero, 1(a0) # h[1] = 0 — the zero register, stored narrow
jr ra
nop
Two things to relish:
kind arrives as a full s32 and hits memory as one byte — no andi, because the store converts (this chapter's refrain, one last time). Keeping value parameters word-sized like this is common and deliberate in real code: it also spares the function the homing ritual a narrow parameter would trigger.sb zero — the hardware's free constant works at every width. A run of sb zero/sh zero at climbing offsets is memory being cleared field by field, and each line is one = 0 assignment in C.
Decoding a packing function is mechanical: each sb is one assignment, offset = index, source register = which parameter (in a1, a2, a3 order). Write the assignments top to bottom and you're done.
The target packs its value arguments into three consecutive byte slots. Read the offsets and match them to the argument registers.
Your task
Write func_802df680 to reproduce the target assembly.