x86 Instruction Set Reference

MOVSX - Move with Sign-Extension

Opcode Mnemonic Description
0F BE /r MOVSX r16,r/m8 Move byte to word with sign-extension.
0F BE /r MOVSX r32,r/m8 Move byte to doubleword, sign-extension.
0F BF /r MOVSX r32,r/m16 Move word to doubleword, sign-extension.
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 IA-32 Intel Architecture Software Developer's Manual, Volume 1). The size of the converted value depends on the operand-size attribute.
Operation 
Destination = SignExtend(Source);
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.
#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.
Real-Address Mode Exceptions
#GPIf a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
#GPIf a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
Virtual-8086 Mode Exceptions
#GP(0)If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
#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.