Encoding:

Format:

ADDU16 rd, rs, rt

Purpose:

Add Unsigned Word (16-bit instr size)

To add 32-bit integers

Description:

GPR[rd] = GPR[rs] + GPR[rt]

The 32-bit word value in GPR rt is added to the 32-bit value in GPR rs, and the 32-bit arithmetic result is signextended and placed into GPR rd.

No Integer Overflow exception occurs under any circumstances.

Restrictions:

The 3-bit register fields can only specify GPRs $2-$7, $16, $17.

If either GPR rt or GPR rs does not contain sign-extended 32-bit values (bits 63..31 equal), then the result of the operation is UNPREDICTABLE.

Availability and Compatibility:

This instruction has been recoded for Release 6.

Operation:

if NotWordValue(GPR[rs]) or NotWordValue(GPR[rt]) then 
   UNPREDICTABLE
endif
temp = GPR[rs] + GPR[rt]
GPR[rd] = sign_extend(temp31..0)

Exceptions:

None

Programming Notes:

The term "unsigned" in the instruction name is a misnomer; this operation is 32-bit modulo arithmetic that does not trap on overflow. This instruction is appropriate for unsigned arithmetic, such as address arithmetic, or integer arithmetic environments that ignore overflow, such as C language arithmetic.