Middle Checklist
Since this is a long topic, it is good to have an intermediate checklist. So far, we have discussed basic arithmetic and logical instructions as well as their immediate variants (if any). The summary is shown below:
Basic
| Operation | Opcode | MipC |
|---|---|---|
| Addition | add $rd, $rs, $rt |
$rd = $rs + $rt |
| Subtraction | sub $rd, $rs, $rt |
$rd = $rs - $rt |
| Shift Left Logical | sll $rd, $rt, C5 |
$rd = $rt << C5 |
| Shift Right Logical | add $rd, $rt, C5 |
$rd = $rt >> C5 |
| Bitwise AND | and $rd, $rs, $rt |
$rd = $rs & $rt |
| Bitwise OR | or $rd, $rs, $rt |
$rd = $rs | $rt |
| Bitwise XOR | xor $rd, $rs, $rt |
$rd = $rs ^ $rt |
| Bitwise NOR | nor $rd, $rs, $rt |
currently unavailable |
Shift
Note that the second operand is $rt instead of $rs.
Additionally, C5 is basically 5-bits unsigned integer.
Why only 5-bits?
Well, 25 = 32.
If we shift left/right 32-bits, we get all 0.
So any number greater than 32 is immaterial.
Immediate
| Operation | Opcode | MipC |
|---|---|---|
| Addition | addi $rt, $rs, C162s |
$rt = $rs + C162s |
| Bitwise AND | andi $rt, $rs, C16 |
$rt = $rs & C16 |
| Bitwise OR | ori $rt, $rs, C16 |
$rt = $rs | C16 |
| Bitwise XOR | xori $rt, $rs, C16 |
$rt = $rs ^ C16 |
Note how the destination register (i.e., $rd) is now changed to target register (i.e., $rt).
Arithmetic
C162s is 16-bits 2s complement (i.e., signed integer).
The range is from -215 to 215-1.
These values are sign-extended.
In other words, we extend it from 16-bits to 32-bits by duplicating the most significant bit (MSB).
If the MSB is 0, we append 0 to the front.
If the MSB is 1, we append 1 to the front.
Logical
C16 is 16-bits unsigned integer.
The range is from 0 to 216-1.
However, they are typically given as 16-bit patterns (i.e., 0xAAAA) instead.
These values are bit-extended.
In other words, we extend it from 16-bits to 32-bits by appending 0.