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Task/Least-common-multiple/Assembly/least-common-multiple..as

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+; lcm.asm: calculates the least common multiple
+; of two positive integers
+;
+; nasm x86_64 assembly (linux) with libc
+; assemble: nasm -felf64 lcm.asm; gcc lcm.o
+; usage: ./a.out [number1] [number2]
+
+    global main
+    extern printf ; c function: prints formatted output
+    extern strtol ; c function: converts strings to longs
+
+    section .text
+
+main:
+    push rbp    ; set up stack frame
+
+    ; rdi contains argc
+    ; if less than 3, exit
+    cmp rdi, 3
+    jl incorrect_usage
+
+    ; push first argument as number
+    push rsi
+    mov rdi, [rsi+8]
+    mov rsi, 0
+    mov rdx, 10 ; base 10
+    call strtol
+    pop rsi
+    push rax
+
+    ; push second argument as number
+    push rsi
+    mov rdi, [rsi+16]
+    mov rsi, 0
+    mov rdx, 10 ; base 10
+    call strtol
+    pop rsi
+    push rax
+
+    ; pop arguments and call get_gcd
+    pop rdi
+    pop rsi
+    call get_gcd
+
+    ; print value
+    mov rdi, print_number
+    mov rsi, rax
+    call printf
+
+    ; exit
+    mov rax, 0  ; 0--exit success
+    pop rbp
+    ret
+
+incorrect_usage:
+    mov rdi, bad_use_string
+    ; rsi already contains argv
+    mov rsi, [rsi]
+    call printf
+    mov rax, 0  ; 0--exit success
+    pop rbp
+    ret
+
+bad_use_string:
+    db "Usage: %s [number1] [number2]",10,0
+
+print_number:
+    db "%d",10,0
+
+get_gcd:
+    push rbp    ; set up stack frame
+    mov rax, 0
+    jmp loop
+
+loop:
+    ; keep adding the first argument
+    ; to itself until a multiple
+    ; is found. then, return
+    add rax, rdi
+    push rax
+    mov rdx, 0
+    div rsi
+    cmp rdx, 0
+    pop rax
+    je gcd_found
+    jmp loop
+
+gcd_found:
+    pop rbp
+    ret