Bit Shifts

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Mnemonic	Description	Cycles
lsl	logical shift left	1
lsr	logical shift Right	1
rol	rotate left through carry	1
ror	rotate right through carry	1
asr	arithmetic shift right	1

::lsl

Performs logical bit shift to LEFT with a zero.

ldi   r16, 0b00001111
lsl   r16   ; r16 :> 0b00011110
<---

::lsr

Performs logical bit shift to RIGHT with a zero.

ldi   r16, 0b00001111
lsr   r16   ; r16 :> 0b0000111
-->

::rol

Similar with lsl. Adds zero or one according to the carry bit (status register).

ldi   r16, 0b10101010
ldi   r17, 0b10101010

lsl   r16   ; r16 :> 0b01010100
rol   r17   ; r17 :> 0b01010101 adds last bit shift to first bit

::ror

Similar with lsr. Adds zero or one according to the carry bit (status register).

ldi   r16, 0b10101010
ldi   r17, 0b10101010

lsl   r16   ; r16 :> 0b01010101
ror   r17   ; r17 :> 0b01010101 adds previous first bit shift to last bit

::asr

Without changing sign of the value, this allows us to divide the value with 2. This keeps 7^th Bit unchanged. And 6^th Bit will be carry bit.

ldi   r16, 0b10000001   ; -127
asr   r16   ; r16 :> 0b11000000 = -64

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