AVR assembly language on Division
To divide by two: 

LSR r4 which push b0 to to carry b1 to b0, ... b7 to b6 and zero to b7



ROR r5 which will push b0 to to carry b1 to b0, ... b7 to b6 and carry that is the b0 from r4 to b7



To divide by 4 use the sequence twice

LSL is used for multiplication. 

The pictures are from Microchip Website AVR Assembler Instructions