Nintendo Ultra64 Programmer's Manual page 157

ADDI
31 26 25
ADDI
0 0 1 0 0 0
6
Format:
addi rt, rs, immediate
Description:
immediate
The 16-bit
result. The result is placed into general register
Since the RSP does not signal an overflow exception for ADDI, this command behaves identically
to ADDIU.
Operation:
GPR [rt]  GPR[rs] + ((immediate
T:
Exceptions:
None
Revision 1.0
Add Immediate
21 20 16 15
rs rt
5 5
is sign-extended and added to the contents of general register
immediate
16
rt.
16
) || immediate )
15 15...0
ADDI
0
rs
to form the
157