Set unit cannot exist(but can), return r2 = 0

0017fd80: 000410c0 sll r2,r4,0x03
0017fd84: 00441023 subu r2,r2,r4
0017fd88: 00021180 sll r2,r2,0x06
0017fd8c: 3c038019 lui r3,0x8019
0017fd90: 246308cc addiu r3,r3,0x08cc
0017fd94: 00431021 addu r2,r2,r3
0017fd98: 340300ff ori r3,r0,0x00ff
0017fd9c: a0430001 sb r3,0x0001(r2)
0017fda0: a0400183 sb r0,0x0183(r2)
0017fda4: 03e00008 jr r31
0017fda8: 00001021 addu r2,r0,r0