Nand2Tetris Hack Divide By 2 (Right Shift)

// Divides R0 by 2 and stores the dividend in R1 and remainder in R2
// (R0, R1, R2 refer to RAM[0], RAM[1], and RAM[2], respectively.)

// how : counter goes from 2 to 32768 ( doubling each time )
// start with 1 and dump result of the AND in R2
// start off setting R1 to 0 and after that, based on result of the AND of
// counter with R0, you either OR R1 with counter or do nothing

@R1
M = 0
D = 1
@R0
D = M & D
@R2
M = D // remainder captured
@lagcount
M = 1
@2
D = A
@counter
M = D

(LOOP)
@R0
D = M & D // we're expecting D (pre) to already have the counter value based on knowing our code
@NO_ACTION
D, JEQ
@lagcount // else, we need to OR R1 with the lagging counter
D = M
@R1
M = M | D
(NO_ACTION)
@16384 // can only load a 15 bit number :)
D = A
D = D + A
@counter
D = M - D
@END
D, JEQ
// else, we need to double counter and double lagcount
@lagcount
D = M
M = M + D
@counter
D = M
MD = M + D

@LOOP
0, JMP

(END)
@END
0, JMP