One function, the whole chapter
Time to read a 64-bit function the way you'd meet one in a real game: several idioms stacked, no labels. First, a worked warm-up that fuses mixed arguments, widening, and the carry chain — tally(base, count), an s64 plus an s32:
sw a0, 0(sp) # only the s64 homes — it came first, in a0:a1
sw a1, 4(sp)
lw t9, 4(sp) # base-low
lw t8, 0(sp) # base-high
sra t6, a2, 31 # count's sign, manufactured on the spot
addu v1, a2, t9 # low sum
sltu at, v1, t9 # the carry
addu v0, at, t6 # carry + count's sign…
addu v0, v0, t8 # …+ base-high
jr ra
nop
Run the checklist and every line files itself: homes at 0/4 place the s64 first (in a0:a1, so no register skipped; the s32 follows in a2). The lone sra-by-31 flags the narrow signed value being widened. The addu/sltu/addu/addu spine is one +. Nine instructions, one line of C.
The target stacks differently. Here's how to attack it — and any 64-bit function from here on:
- Frame first. If there's a prologue, something inside makes a call — and in this chapter, a call means millicode. Find the
jal; its name tells you the operation and the signedness.
- Map the homes and reloads. Which words feed the call, and from which parameter slots?
- Read past the call. Whatever touches
v0:v1 after the jal is arithmetic applied to the call's result — and by now, every post-processing chain you could meet is one you've already named.
Three steps, and a function that once looked like forty lines of noise becomes a single C expression. Go read it.
Your task
Write func_803ed8c0 to reproduce the target assembly.