Two loads feed one operation
Up to now each lesson poked one location. Real code isn't that tidy. It pulls a few values from an array and mashes them into a result. No new trick — just earlier lessons stacked. Load each element on its own, each from its own constant displacement, then run a single arithmetic instruction across the loaded registers.
The loads have to come first. A combine can't fire until both inputs are in registers. The displacements tell you which elements were read; divide each by the element size, same move as the constant-index lesson.
Here's diff_two(q), reading two ints and subtracting the first from the third:
lwz r4, 0(r3) # q[0]
lwz r0, 8(r3) # q[2] (displacement 8 / 4 = index 2)
subf r3, r4, r0 # r0 - r4 = q[2] - q[0]
blr
Two separate loads, one subf (subf rD, rA, rB gives rB − rA). The 0 and 8 say which elements got read; the subf says what's done with them. Your target has the same two-loads-then-combine shape. Read its displacements and its combining instruction and they'll point you at the elements and the operation.
Your task
Write func_801ae9bc to reproduce the assembly above.