Bitwise Instructions
| A | B | A AND B | A OR B | NOT A | A XOR B | A BIC B |
|---|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 1 | 0 | 0 |
| 0 | 1 | 0 | 1 | 1 | 1 | 0 |
| 1 | 0 | 0 | 1 | 0 | 1 | 1 |
| 1 | 1 | 1 | 1 | 0 | 0 | 0 |
XOR
[A AND (NOT B)] OR [(NOT A) AND B]
A XOR 0 = A
A XOR 1 = NOT A
| In ARM | In C | |
|---|---|---|
| AND | AND r0, r1,r2 | r0 = r1 & r2; |
| OR | ORR r0, r1, r2 | r0 = r1 || r2; |
| XOR | EOR r0, r1, r2 | r0 = r1 ^ r2; |
| BIC | BIC r0, r1, r2 | r0 = r1 & (~r2) |
| NOT | MVN r0, r1 | r0 = ~r1 |
ARM
MVN r0, #0
-1 is stored in r0.
#0 is automatically extended to 32 bits of 0’s. Flipping 32 0’s to 32 1’s gets -1 in two’s complement.
ADD r3, r0, r1
r1 is the mask.
Bit shifts and multiplication
LSL
Logical shift by n bits – unsigned multiplication by 2n
LSL r0, r0, #4
The above code multiplies r0 with 24, i.e. 16.
LSR
Logical shift by n bits – unsigned division by 2n
ASR
Arithmetic shift by n bits – signed division by 2n
ROR
Logical rotate by n bits – 32 bit rotate
ror r1, r0, #1
Rotate amount is non-negative.
Shift 4 bits: r0 = 0x12345678, r1 would be 0x81234567.
Shift 8 bits: r0 = 0x12345678, r1 would be 0x78123456.
| ARM | C | |
|---|---|---|
| LSL | LSL r0, r1, #n | r0 = r1 << n; |
| LSR | LSR r0, r1, #n | r0 = (unsigned int) r1 >> n; |
| ASR | ASR r0, r1, #n | r0 = r1 >> n; |
| ROR | ROR r0, r1, #n | UNFINISHED |
RSB
Reverse subtract, used for easier multiplication
RSB r0, r1, r2 @ r0 = r2 - r1
RSB r10, r9, r9, LSL #3 @ r10 = r9 * (8 - 1)
Addressing modes
ADD r0, r1, r2, LSL #2 @ r0 = r1 + (r2 << 2)
LSL r2, r2, #r2 ADD r0, r1, r2
LDR r0, [r1, r2] @ r0 = [r1 + r2]
LDR r0, [r1, r2, LSL #n] @ LSL applied to r2
ADD r0, r1, #0xff, #8 @ r0 = r1 + 0xff000000 @ performs ROR, #8 is the rot
ADD r2, r2, LSL, #2 @ r2 = 5 * r2Published on November 6, 2015