Loops
| The LOOP instruction | |
| The register pattern | |
| Nested loops |
The LOOP instruction
LOOP decrements RCX and jumps to a label while RCX is not zero. It is one instruction, but modern CPUs handle the explicit DEC and JNZ pair faster, so expect to see both styles:
mov rcx, 10
print_loop:
; body here
loop print_loop ; rcx = rcx - 1, jump if not zero
The register pattern
The explicit pattern gives you control over the counter and the exit condition:
mov rcx, 10
print_loop:
; body here
dec rcx
jnz print_loop
Nested loops
Save the outer counter before entering the inner loop, on the stack or in a spare register, and restore it after. RCX is the classic counter, so nested loops must protect it.
Next: The stack
Article author: Arthur Isaev
