stackmachine-go/3n+1.asm at master · bristol-d/stackmachine-go · GitHub

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; 3n+1 problem in stack S16 assembly
; given a number N, repeat until you reach 1:
; if N is even, replace with N/2
; if N is odd, replace with 3N + 1
; put all the numbers encountered on the way in data memory
; starting at location 1, with location 0 used as a pointer
; an optional interrupt occurs before every number in the sequence

            PUSH array  ; initialise data pointer to array (1)
            STOR index
            PUSH #7     ; the original N
start:      DUP         ; store in data memory
            LOAD index
            STRS
            LOAD index  ; increase pointer in data[0]
            PUSH #1
            ADD
            STOR index
            ; INT       ; interrupt - enable if needed
            DUP         ; make a copy for testing if it's 1
            PUSH #1
            CEQ
            JT end
            DUP         ; make a copy for the even test
            PUSH #1
            AND
            JT odd
            PUSH #1
            SHR         ; it's even, divide by 2
            J start
odd:        PUSH #3
            MUL
            PUSH #1
            ADD
            J start
end:        HALT

.DATA
index:
array: