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movsxd

Move doubleword with sign extension

Copies a 32-bit source into a register, sign-extending for a 64-bit destination.

x86-64 and later

Intel's reference: MOVSX/MOVSXD

Used in
CFPFAFZFSFDFOF –––––––
  • Changes no flag

Forms

  • movsxd rax, eax

Operands

reg
The destination register. Its width is selected independently of the source width; widening uses a larger destination.
r/m32
A 32-bit general-purpose register or doubleword in memory, for example eax or dword [rsi].

Its usual use is movsxd rax, ecx: copy 32 bits and sign-extend them to 64 bits. Writing eax with an ordinary move would instead clear bits 63–32 of rax.

NASM also accepts 32- and 16-bit destinations: movsxd eax, ecx copies the 32-bit value and clears the upper half of rax; movsxd ax, ecx retains the low 16 bits. Neither widens the source. movsxd rax, eax can use the same encoding as cdqe.

global _start

section .text
_start:
        mov rax, 12
        mov rbx, 5
        mov rcx, 3
        mov rsi, 9

        movsxd rax, ebx

        mov rax, 60         ; syscall 60: exit
        xor rdi, rdi
        syscall