Everything at once
A real struct function reads a field, changes it, tests it, and touches a neighbor on one path — every idiom from this chapter in ten lines. Here's charge, which feeds energy into a cell and latches a flag when it tops out:
typedef struct {
u8 state; // offset 0
u8 flags; // offset 1 — bit 3 = "charged"
s16 energy; // offset 2
} Cell;
void charge(Cell *c, s32 amt) {
c->energy += amt;
if (c->energy >= 100) {
c->energy = 100;
c->flags |= 8;
}
}
0: lh t6, 2(a0) # read energy
4: addu t7, t6, a1 # + amt
8: sh t7, 2(a0) # write it back
c: lh t8, 2(a0) # re-read it for the test
10: slti at, t8, 100 # energy < 100 ?
14: bnez at, 0x30 # yes → skip the whole if-body
18: nop
1c: lbu t0, 1(a0) # read flags…
20: addiu t9, zero, 100
24: sh t9, 2(a0) # energy = 100
28: ori t1, t0, 0x8 # …set bit 3…
2c: sb t1, 1(a0) # …write flags back
30: jr ra
34: nop
Walk it idiom by idiom:
- The RMW sandwich opens:
lh/addu/sh at offset 2 is energy += amt, width and signedness read straight off the lh.
- The re-read at
0xc is the narrow-field tax: energy lives in memory as 16 bits, so testing its post-store value means loading it again — sh then lh at the same offset. The compiler will not reuse t7, because the store just truncated it.
slti + bnez is the flipped guard: the C says >= 100, the branch jumps away on < 100. Un-flip it to recover the source.- Inside the body, a constant store and a flag-set interleave — the scheduler shuffled them, but offset 2 lines are
energy and offset 1 lines are flags, so sorting them back into C is just reading offsets.
The target is the same anatomy pointed the other way: a stat gets drained, floored rather than capped, and a flag cleared rather than set when it bottoms out. The Unit layout below names every offset you'll meet — let the widths, the branch, and the mask dictate the C.
Your task
Write func_8014e3e8 to reproduce the target assembly.