MOVBE
— Move Data After Swapping Bytes
Opcode/Instruction |
Op/En |
64/32 bit Mode Support |
CPUID Feature Flag |
Description |
0F 38 F0 /r MOVBE r16, m16 |
RM |
V/V |
MOVBE |
Reverse byte order in m16 and move to r16. |
0F 38 F0 /r MOVBE r32, m32 |
RM |
V/V |
MOVBE |
Reverse byte order in m32 and move to r32. |
REX.W + 0F 38 F0 /r MOVBE r64, m64 |
RM |
V/N.E. |
MOVBE |
Reverse byte order in m64 and move to r64. |
0F 38 F1 /r MOVBE m16, r16 |
MR |
V/V |
MOVBE |
Reverse byte order in r16 and move to m16. |
0F 38 F1 /r MOVBE m32, r32 |
MR |
V/V |
MOVBE |
Reverse byte order in r32 and move to m32. |
REX.W + 0F 38 F1 /r MOVBE m64, r64 |
MR |
V/N.E. |
MOVBE |
Reverse byte order in r64 and move to m64. |
Instruction Operand Encoding
¶
Op/En |
Operand 1 |
Operand 2 |
Operand 3 |
Operand 4 |
RM |
ModRM:reg (w) |
ModRM:r/m (r) |
N/A |
N/A |
MR |
ModRM:r/m (w) |
ModRM:reg (r) |
N/A |
N/A |
Description
¶
Performs a byte swap operation on the data copied from the second operand (source operand) and store the result in the first operand (destination operand). The source operand can be a general-purpose register, or memory location; the destination register can be a general-purpose register, or a memory location; however, both operands can not be registers, and only one operand can be a memory location. Both operands must be the same size, which can be a word, a doubleword or quadword.
The MOVBE instruction is provided for swapping the bytes on a read from memory or on a write to memory; thus providing support for converting little-endian values to big-endian format and vice versa.
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
¶
TEMP := SRC
IF ( OperandSize = 16)
THEN
DEST[7:0] := TEMP[15:8];
DEST[15:8] := TEMP[7:0];
ELES IF ( OperandSize = 32)
DEST[7:0] := TEMP[31:24];
DEST[15:8] := TEMP[23:16];
DEST[23:16] := TEMP[15:8];
DEST[31:23] := TEMP[7:0];
ELSE IF ( OperandSize = 64)
DEST[7:0] := TEMP[63:56];
DEST[15:8] := TEMP[55:48];
DEST[23:16] := TEMP[47:40];
DEST[31:24] := TEMP[39:32];
DEST[39:32] := TEMP[31:24];
DEST[47:40] := TEMP[23:16];
DEST[55:48] := TEMP[15:8];
DEST[63:56] := TEMP[7:0];
FI;
Flags Affected
¶
None.
Protected Mode Exceptions
¶
#GP(0) |
If the destination operand is in a non-writable segment. |
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 CPUID.01H:ECX.MOVBE[bit 22] = 0. |
If the LOCK prefix is used. |
If REP (F3H) 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 CPUID.01H:ECX.MOVBE[bit 22] = 0. |
If the LOCK prefix is used. |
If REP (F3H) 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. |
#AC(0) |
If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3. |
#UD |
If CPUID.01H:ECX.MOVBE[bit 22] = 0. |
If the LOCK prefix is used. |
If REP (F3H) prefix is used. |
If REPNE (F2H) prefix is used and CPUID.01H:ECX.SSE4_2[bit 20] = 0. |
Compatibility Mode Exceptions
¶
Same exceptions as in protected mode.
64-Bit Mode Exceptions
¶
#GP(0) |
If the memory address is in a non-canonical form. |
#SS(0) |
If the stack 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 CPUID.01H:ECX.MOVBE[bit 22] = 0. |
If the LOCK prefix is used. |
If REP (F3H) prefix is used. |