MOVSX/MOVSXD—Move with Sign-Extension

Opcode	Instruction	Op/En	64-Bit Mode	Compat/Leg Mode	Description
0F BE /r	MOVSX r16, r/m8	RM	Valid	Valid	Move byte to word with sign-extension.
0F BE /r	MOVSX r32, r/m8	RM	Valid	Valid	Move byte to doubleword with sign-extension.
REX + 0F BE /r	MOVSX r64, r/m8*	RM	Valid	N.E.	Move byte to quadword with sign-extension.
0F BF /r	MOVSX r32, r/m16	RM	Valid	Valid	Move word to doubleword, with sign-extension.
REX.W + 0F BF /r	MOVSX r64, r/m16	RM	Valid	N.E.	Move word to quadword with sign-extension.
REX.W** + 63 /r	MOVSXD r64, r/m32	RM	Valid	N.E.	Move doubleword to quadword with sign-extension.

NOTES:

*In 64-bit mode, r/m8 can not be encoded to access the following byte registers if a REX prefix is used: AH, BH, CH, DH.

**The use of MOVSXD without REX.W in 64-bit mode is discouraged, Regular MOV should be used instead of using MOVSXD without REX.W.

Instruction Operand Encoding

Op/En	Operand 1	Operand 2	Operand 3	Operand 4
RM	ModRM:reg (w)	ModRM:r/m (r)	NA	NA

Description

Copies the contents of the source operand (register or memory location) to the destination operand (register) and sign extends the value to 16 or 32 bits (see Figure 7-6 in the Intel® 64 and IA-32 Architectures Software Devel-oper’s Manual, Volume 1). The size of the converted value depends on the operand-size attribute.

In 64-bit mode, the instruction’s default operation size is 32 bits. Use of the REX.R prefix permits access to addi-tional registers (R8-R15). Use of the REX.W prefix promotes operation to 64 bits. See the summary chart at the beginning of this section for encoding data and limits.

Operation

DEST ← SignExtend(SRC);

Flags Affected

None.

Protected Mode Exceptions

#GP(0)	If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit. If the DS, ES, FS, or GS register contains a NULL segment selector.
#SS(0)	If a memory operand effective address is outside the SS segment limit.
#PF(fault-code)	If a page fault occurs.
#AC(0)	If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3.
#UD	If the LOCK prefix is used.

Real-Address Mode Exceptions

#GP	If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
#SS	If a memory operand effective address is outside the SS segment limit.
#UD	If the LOCK prefix is used.

Virtual-8086 Mode Exceptions

#GP(0)	If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
#SS(0)	If a memory operand effective address is outside the SS segment limit.
#PF(fault-code)	If a page fault occurs.
#UD	If the LOCK prefix is used.

Compatibility Mode Exceptions

Same exceptions as in protected mode.

64-Bit Mode Exceptions

#SS(0)	If a memory address referencing the SS segment is in a non-canonical form.
#GP(0)	If the memory address is in a non-canonical form.
#PF(fault-code)	If a page fault occurs.
#AC(0)	If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3.
#UD	If the LOCK prefix is used.