Unit doesn't exist/deadcrystaltreasurepetrify/being ridden check

Unit doesn't exist/deadcrystaltreasurepetrify/being ridden check
001835a8: 90830001 lbu r3,0x0001(r4)
001835ac: 340200ff ori r2,r0,0x00ff
001835b0: 1062000f beq r3,r2,0x001835f0		jump if unit doesn't exist
001835b4: 34020001 ori r2,r0,0x0001
001835b8: 90820058 lbu r2,0x0058(r4)
001835bc: 00000000 nop
001835c0: 30420060 andi r2,r2,0x0060
001835c4: 1440000a bne r2,r0,0x001835f0		jump if unit is dead or crystal
001835c8: 34020001 ori r2,r0,0x0001
001835cc: 90820059 lbu r2,0x0059(r4)
001835d0: 00000000 nop
001835d4: 30420081 andi r2,r2,0x0081
001835d8: 14400005 bne r2,r0,0x001835f0		jump if unit is treasure or petrify
001835dc: 34020001 ori r2,r0,0x0001
001835e0: 90820182 lbu r2,0x0182(r4)
001835e4: 00000000 nop
001835e8: 30420040 andi r2,r2,0x0040		r2 = 1 if unit being ridden
001835ec: 0002102b sltu r2,r0,r2		r2 = 1 if any of above are true
001835f0: 03e00008 jr r31

Return Locations

001834dc: - Routine at 1834bc
001837cc: - Calculate AT List