Scaled addressing in Assembly

base + index * size reaches array slots in one operand.

; Scaled addressing: base + index * size reaches array slots.
        global _start

        section .data
nums:   dq 12, 45, 3, 8
COUNT:  equ 4

        section .text
_start:
        xor rax, rax            ; total
        xor rcx, rcx            ; index
.loop:
        add rax, [nums + rcx * 8]
        inc rcx
        cmp rcx, COUNT
        jl .loop

        mov rdi, rax            ; 68
        mov rax, 60             ; exit code 68
        syscall

How it works

1. dq 12, 45, 3, 8 lays out four quadwords.
2. [nums + rcx * 8] scales the index by the element size.
3. The total, 68, exits the program.

Keywords and builtins used here

• add
• cmp
• dq
• equ
• global
• inc
• jl
• mov
• rax
• rcx
• rdi
• section
• syscall
• xor

The run, in numbers

Lines

20

Characters to type

357

Tokens

60

Three-star pace

55 tpm

At the three-star pace of 55 tokens a minute, this run takes about 65 seconds.

Type this snippet

Step 1 of 4 in Memory & strings, step 22 of 31 in Language basics.

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