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# Shift operations

Register shift operations move the bits in a register left or right by a specified number of bits, called the shift length.

Register shift can be performed:

• Directly by the instructions `ASR`, `LSR`, `LSL`, `ROR`, and `RRX`, and the result is written to a destination register.

• During the calculation of `Operand2` by the instructions that specify the second operand as a register with shift. The result is used by the instruction.

The permitted shift lengths depend on the shift type and the instruction, see the individual instruction description or the flexible second operand description. If the shift length is 0, no shift occurs. Register shift operations update the carry flag except when the specified shift length is 0.

## Arithmetic shift right (ASR)

Arithmetic shift right by n bits moves the left-hand 32-n bits of a register to the right by n places, into the right-hand 32-n bits of the result. It copies the original bit of the register into the left-hand n bits of the result.

You can use the `ASR #n` operation to divide the value in the register `Rm` by 2`n`, with the result being rounded towards negative-infinity.

When the instruction is `ASRS` or when ```ASR #n``` is used in `Operand2` with the instructions `MOVS`, `MVNS`, `ANDS`, `ORRS`, `ORNS`, `EORS`, `BICS`, `TEQ` or `TST`, the carry flag is updated to the last bit shifted out, bit[`n`-1], of the register `Rm`.

### Note

• If `n` is 32 or more, then all the bits in the result are set to the value of bit of `Rm`.

• If `n` is 32 or more and the carry flag is updated, it is updated to the value of bit of `Rm`.

Figure C2-1 ASR #3 ## Logical shift right (LSR)

Logical shift right by n bits moves the left-hand 32-n bits of a register to the right by n places, into the right-hand 32-n bits of the result. It sets the left-hand n bits of the result to 0.

You can use the `LSR #n` operation to divide the value in the register `Rm` by 2`n`, if the value is regarded as an unsigned integer.

When the instruction is `LSRS` or when``` LSR #n``` is used in `Operand2` with the instructions `MOVS`, `MVNS`, `ANDS`, `ORRS`, `ORNS`, `EORS`, `BICS`, `TEQ` or `TST`, the carry flag is updated to the last bit shifted out, bit[`n`-1], of the register `Rm`.

### Note

• If `n` is 32 or more, then all the bits in the result are cleared to 0.

• If `n` is 33 or more and the carry flag is updated, it is updated to 0.

Figure C2-2 LSR #3 ## Logical shift left (LSL)

Logical shift left by n bits moves the right-hand 32-n bits of a register to the left by n places, into the left-hand 32-n bits of the result. It sets the right-hand `n` bits of the result to 0.

You can use the `LSL #n` operation to multiply the value in the register `Rm` by 2`n`, if the value is regarded as an unsigned integer or a two's complement signed integer. Overflow can occur without warning.

When the instruction is `LSLS` or when ```LSL #n```, with non-zero `n`, is used in `Operand2` with the instructions `MOVS`, `MVNS`, `ANDS`, `ORRS`, `ORNS`, `EORS`, `BICS`, `TEQ` or `TST`, the carry flag is updated to the last bit shifted out, bit[`32`-`n`], of the register `Rm`. These instructions do not affect the carry flag when used with LSL #0.

### Note

• If `n` is 32 or more, then all the bits in the result are cleared to 0.

• If `n` is 33 or more and the carry flag is updated, it is updated to 0.

Figure C2-3 LSL #3 ## Rotate right (ROR)

Rotate right by n bits moves the left-hand 32-n bits of a register to the right by n places, into the right-hand 32-n bits of the result. It also moves the right-hand n bits of the register into the left-hand n bits of the result.

When the instruction is `RORS` or when ```ROR #n``` is used in `Operand2` with the instructions `MOVS`, `MVNS`, `ANDS`, `ORRS`, `ORNS`, `EORS`, `BICS`, `TEQ` or `TST`, the carry flag is updated to the last bit rotation, bit[`n`-1], of the register `Rm`.

### Note

• If `n` is 32, then the value of the result is same as the value in `Rm`, and if the carry flag is updated, it is updated to bit of `Rm`.

• `ROR` with shift length, `n`, more than 32 is the same as `ROR` with shift length `n`-32.

Figure C2-4 ROR #3 ## Rotate right with extend (RRX)

Rotate right with extend moves the bits of a register to the right by one bit. It copies the carry flag into bit of the result.

When the instruction is `RRXS` or when RRX is used in `Operand2` with the instructions `MOVS`, `MVNS`, `ANDS`, `ORRS`, `ORNS`, `EORS`, `BICS`, `TEQ` or `TST`, the carry flag is updated to bit of the register `Rm`.

Figure C2-5 RRX 