Intel 253666-024US - Manual (Page 731)

Vol. 2A 3-685
INSTRUCTION SET REFERENCE, A-M
MOVSX/MOVSXD—Move with Sign-Extension
MOVSX/MOVSXD—Move with Sign-Extension
Description
Copies the contents of the source operand (register or memory location) to the desti-
nation 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 Developer’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 additional 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.
Opcode Instruction 64-Bit
Mode
Compat/
Leg Mode
Description
0F BE /r MOVSX r16, r/m8 Valid Valid Move byte to word with sign-
extension.
0F BE /r MOVSX r32, r/m8 Valid Valid Move byte to doubleword
with sign-extension.
REX + 0F BE /r MOVSX r64, r/m8* Valid N.E. Move byte to quadword with
sign-extension.
0F BF /r MOVSX r32, r/m16 Valid Valid Move word to doubleword,
with sign-extension.
REX.W + 0F BF /r MOVSX r64, r/m16 Valid N.E. Move word to quadword with
sign-extension.
REX.W** + 63 /r MOVSXD r64, r/m32 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.