TSK3000A Core Instruction - ADDI, ADDIU
Instruction: Add Immediate Word
Assembler Format: addi rB, rA, IMM16
Example: addi $3, $4, 0x1234
Description: Sign-extends the 16-bit immediate value, IMM16, adds it to the contents of GPR rA and puts the result in GPR rB.
Operation: rB <-- rA + SignExtend(IMM16)
Instruction Type: I-Type
Instruction Fields: rA = Register index of operand A
rB = Register index of destination
IMM16 = 16-bit immediate data value
Encoding:
| 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
| 0 | 0 | 1 | 0 | 0 | 1 | rA | rB | IMM16 | |||||||||||||||||||||||
Latency: 1
Notes
The following code example illustrates how overflow detection can be handled, in software, when adding two signed operands:
addi rB, rA, IMM16
xor rC, rB, rA -----compare sign of sum and operand rA
xori rD, rB, IMM16 -----compare sign of sum and IMM16
and rC, rC, rD -----bitwise logically AND the comparison values
slt rC, rC, $0 -----if result less than '0', flag overflow
rC will be set to '1' if an overflow occurred, otherwise it will be set to '0'