movsxd

x86-64 and later

Move Doubleword to Quadword with Sign-Extension

movsxd rax, eax | movsxd reg16, r/m32 | movsxd reg32, r/m32 | movsxd reg64, r/m32

Copies a 32 bit source into a 64 bit register, sign extending it. This is the instruction to reach for when a signed 32 bit value has to become a 64 bit one, because the ordinary mov eax, ... zero extends instead: writing any 32 bit register clears the top half of its 64 bit name.

Forms

Every form of movsxd the assembler accepts, from NASM's own instruction table. The second column is the processor that introduced the form; a badge marks a form that needs an extension, that is lockable, or that long mode dropped.

Form	Since	Notes
movsxd rax, eax	x86-64	long
movsxd reg16, r/m32	x86-64	long
movsxd reg32, r/m32	x86-64	long
movsxd reg64, r/m32	x86-64	long