strlen by hand in Assembly

Walk bytes until the zero terminator.

; Walk bytes until the zero terminator: strlen by hand.
        global _start

        section .data
name:   db "workbench", 0

        section .text
_start:
        lea rsi, [name]
        xor rcx, rcx
.scan:
        cmp byte [rsi + rcx], 0
        je .done
        inc rcx
        jmp .scan
.done:
        mov rdi, rcx            ; length 9
        mov rax, 60             ; exit code 9
        syscall

How it works

1. db "workbench", 0 stores the string and its terminator.
2. cmp byte [rsi + rcx], 0 reads one byte at a time.
3. The count, 9, is the exit code.

Keywords and builtins used here

• byte
• cmp
• db
• global
• inc
• je
• jmp
• lea
• mov
• rax
• rcx
• rdi
• rsi
• section
• syscall
• xor

The run, in numbers

Lines

19

Characters to type

308

Tokens

50

Three-star pace

55 tpm

At the three-star pace of 55 tokens a minute, this run takes about 55 seconds.

Type this snippet

Step 3 of 4 in Memory & strings, step 24 of 31 in Language basics.

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