The loop shape in Assembly

A label, a compare, a conditional jump back: every loop ever.

; A loop is a label, a compare, and a conditional jump back.
        global _start

        section .text
_start:
        xor rax, rax            ; sum
        mov rcx, 1              ; counter
.top:
        add rax, rcx
        inc rcx
        cmp rcx, 10
        jle .top                ; while rcx <= 10

        mov rdi, rax            ; 1+2+...+10 = 55
        mov rax, 60             ; exit code 55
        syscall

How it works

1. .top: is a local label under _start.
2. cmp sets flags; jle jumps while rcx <= 10.
3. The Gauss sum 1..10 = 55 leaves as the exit code.

Keywords and builtins used here

• add
• cmp
• global
• inc
• jle
• mov
• rax
• rcx
• rdi
• section
• syscall
• xor

The run, in numbers

Lines

16

Characters to type

332

Tokens

41

Three-star pace

60 tpm

At the three-star pace of 60 tokens a minute, this run takes about 41 seconds.

Type this snippet

Step 2 of 4 in Control flow, step 12 of 31 in Language basics.

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