A float step with a clamp
Here's the capstone, leaning on nearly the whole chapter at once. Struct fields loaded without touching the constant pool. A chained multiply. The lerp idiom: fsubs into fmadds. A one-branch clamp from fcmpo and fmr. A store to close it off. Read the fields, interpolate toward a target, clamp, write back — that's the per-frame update pattern game actor code is built from.
Take body_step(b, dt). It nudges a position forward by drag-scaled velocity and refuses to let it drop below zero:
lfs f0, 8(r3) # b->drag
lfs f2, 4(r3) # b->vel
fmuls f1, f0, f1 # drag * dt
lfs f3, 0(r3) # b->pos
lfs f0, ... # load 0.0f
fmuls f1, f2, f1 # vel * (drag * dt)
fadds f1, f3, f1 # pos + that
fcmpo cr0, f1, f0 # result < 0 ?
bge- .ok # skip clamp when >= 0
fmr f1, f0 # result = 0
.ok:
stfs f1, 0(r3) # b->pos = result
blr
Nothing ever leaves f1. The products pile up there, fadds brings in the base, and fcmpo/bge-/fmr clamps the floor. Then stfs writes the final value back. The branch tests the inverted if, so bge- skips the if (result < 0) body. Exactly one stfs.
On to the target, func_80129fdc. The math before the compare is the lerp idiom. Look for an fsubs taking a difference, an fmadds shaping base + diff * amount, and an fmuls putting that amount together. Past the compare, the fcmpo operands and branch condition name the field that bounds the result, and the stfs offset says where the answer goes.
Its one argument points at this struct:
typedef struct { f32 value; f32 target; f32 rate; } Slider;
Your task
With the Slider struct above, write func_80129fdc to reproduce the assembly above. Compute the interpolated step into one local, clamp it against the relevant field, and store it back.