Bringing the chapter together
This capstone fuses almost everything from the chapter into one realistic update function: pooled-constant–free struct loads, a chained multiply, the lerp idiom (fsubs → fmadds), a compare-and-branch clamp (fcmpo + fmr), and a final store. The shape — read fields, interpolate toward a target, clamp, write back — is exactly the kind of per-frame update that fills game actor code.
Consider body_step(b, dt), which advances a position by a drag-scaled velocity and floors the result at 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
Everything threads through f1: the products build up, the fadds adds the base, the fcmpo/bge-/fmr apply the floor, and stfs writes the single final value back to the struct. The branch uses the inverted if condition (bge- skips the if (result < 0) body), and the lone stfs confirms only one store at the end.
Now decode the target assembly for slider_approach. The arithmetic before the compare is the lerp idiom from earlier — spot the fsubs computing a difference and the fmadds doing base + diff * amount, with an fmuls building that amount. Then read the fcmpo operands and branch condition to find which field bounds the result, and the stfs offset for where it's stored.
The argument points to this struct:
typedef struct { f32 value; f32 target; f32 rate; } Slider;
Your task
With the Slider struct above, write slider_approach taking a Slider* and an f32 dt to reproduce the assembly above. Compute the interpolated step into one local, clamp it against the relevant field, and store it back.