The cheapest function on the machine
The ABI splits the register file in two. r0-r3 carry the first four arguments in, r0 carries the result back out, and all four are scratch: whoever calls you assumes nothing in them survives. r4-r7 are the opposite promise — a function must hand them back exactly as it found them, so touching one costs a save and a restore.
A function that fits inside that first group and calls nobody therefore needs no bookkeeping at all. No push, no sub sp, no saved registers. The first instruction is real work and the last is bx lr, jumping to the return address the caller left in lr. That is a leaf, and it is the only shape on this machine with zero overhead.
Here is one that computes a tile index from a width and a height:
0 mov r2, r0
2 mul r2, r1
4 add r2, r0
6 add r2, r1
8 mov r0, r2
10 bx lr
The function has two parameters, so r2 and r3 arrived holding nothing in particular — and gcc uses r2 as a free workspace. It copies w there, builds the whole expression in it with the two-operand mul and add forms, and only at the end moves the answer into r0 where the caller will look for it. The copy costs an instruction and saves gcc from destroying w, which is still needed after the multiply.
bx lr rather than mov pc, lr is the interworking return: bx restores the caller's instruction set from the low bit of the address, so a Thumb function can be called from ARM code and still come back correctly. Every function you match in this course ends in some form of bx.
Your target is a leaf too. Nothing is saved, so read it knowing that any register it writes before reading was scratch, not an argument.
Your task
Write func_082dd6fc to reproduce the target assembly.