movsw
Move string words
Copies the word at [rsi] to [rdi], then advances rsi and rdi by 2, backward when DF is set.
8086 and later
CFPFAFZFSFDFOF –––––––
- Changes no flag
- Reads DF
Forms
movsw
The w suffix selects an element of 2 bytes. After each element, the instruction increases rsi and rdi by 2 when DF = 0, or decreases rsi and rdi by 2 when DF = 1. In 64-bit mode the default addresses use rsi and rdi. The a32 address-size prefix instead uses esi and edi; 16-bit string addressing is unavailable.
rep repeats until the counter reaches zero. The counter is rcx by default or ecx with a32. If it starts at zero, a repeated instruction accesses no element. The data width is independent of this address and counter width.
global _start
section .data
source: db 1, 2, 3, 4, 5, 6, 7, 8
destination: times 8 db 0
section .text
_start:
cld ; count upwards
mov rsi, source
mov rdi, destination
mov rax, 7
movsw ; copies two bytes
mov rax, 60 ; syscall 60: exit
xor rdi, rdi
syscall