PACKUSWB

Pack with Unsigned Saturation

Opcodes

Hex Mnemonic Encoding Long Mode Legacy Mode Description
66 0F 67 /r PACKUSWB xmm1, xmm2/m128 A Valid Valid Converts 8 signed word integers from xmm1 and 8 signed word integers from xmm2/m128 into 16 unsigned byte integers in xmm1 using unsigned saturation.
0F 67 /r PACKUSWB mm, mm/m64 A Valid Valid Converts 4 signed word integers from mm and 4 signed word integers from mm/m64 into 8 unsigned byte integers in mm using unsigned saturation.

Instruction Operand Encoding

Op/En Operand 0 Operand 1 Operand 2 Operand 3
A NA NA ModRM:r/m (r) ModRM:reg (r, w)

Description

Converts 4 or 8 signed word integers from the destination operand (first operand) and 4 or 8 signed word integers from the source operand (second operand) into 8 or 16 unsigned byte integers and stores the result in the destination operand. (See Figure 4-2 for an example of the packing operation.) If a signed word integer value isbeyond the range of an unsigned byte integer (that is, greater than FFH or less than 00H), the saturated unsigned byte integer value of FFH or 00H, respectively, is stored in the destination.

The PACKUSWB instruction operates on either 64-bit or 128-bit operands. When operating on 64-bit operands, the destination operand must be an MMX technology register and the source operand can be either an MMX technology register or a 64-bit memory location. When operating on 128-bit operands, the destination operand must be an XMM register and the source operand can be either an XMM register or a 128-bit memory location.

In 64-bit mode, using a REX prefix in the form of REX.R permits this instruction to access additional registers (XMM8-XMM15).

Pseudo Code

(* PACKUSWB instruction with 64-bit operands: DEST[7:0] = SaturateSignedWordToUnsignedByte DEST[15:0]; *)
DEST[15:8] = SaturateSignedWordToUnsignedByte DEST[31:16];
DEST[23:16] = SaturateSignedWordToUnsignedByte DEST[47:32];
DEST[31:24] = SaturateSignedWordToUnsignedByte DEST[63:48];
DEST[39:32] = SaturateSignedWordToUnsignedByte SRC[15:0];
DEST[47:40] = SaturateSignedWordToUnsignedByte SRC[31:16];
DEST[55:48] = SaturateSignedWordToUnsignedByte SRC[47:32];
DEST[63:56] = SaturateSignedWordToUnsignedByte SRC[63:48];
(* PACKUSWB instruction with 128-bit operands: DEST[7:0] = SaturateSignedWordToUnsignedByte (DEST[15:0]); *)
DEST[15:8] = SaturateSignedWordToUnsignedByte (DEST[31:16]);
DEST[23:16] = SaturateSignedWordToUnsignedByte (DEST[47:32]);
DEST[31:24] = SaturateSignedWordToUnsignedByte (DEST[63:48]);
DEST[39:32] = SaturateSignedWordToUnsignedByte (DEST[79:64]);
DEST[47:40] = SaturateSignedWordToUnsignedByte (DEST[95:80]);
DEST[55:48] = SaturateSignedWordToUnsignedByte (DEST[111:96]);
DEST[63:56] = SaturateSignedWordToUnsignedByte (DEST[127:112]);
DEST[71:64] = SaturateSignedWordToUnsignedByte (SRC[15:0]);
DEST[79:72] = SaturateSignedWordToUnsignedByte (SRC[31:16]);
DEST[87:80] = SaturateSignedWordToUnsignedByte (SRC[47:32]);
DEST[95:88] = SaturateSignedWordToUnsignedByte (SRC[63:48]);
DEST[103:96] = SaturateSignedWordToUnsignedByte (SRC[79:64]);
DEST[111:104] = SaturateSignedWordToUnsignedByte (SRC[95:80]);
DEST[119:112] = SaturateSignedWordToUnsignedByte (SRC[111:96]);
DEST[127:120] = SaturateSignedWordToUnsignedByte (SRC[127:112]);

Flags Affected

None.

Exceptions

64-Bit Mode Exceptions

Exception Description
#AC(0) (64-bit operations only) If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3.
#PF(fault-code) If a page fault occurs.
#MF (64-bit operations only) If there is a pending x87 FPU exception.
#NM If CR0.TS[bit 3] = 1.
#UD If CR0.EM[bit 2] = 1. (128-bit operations only) If CR4.OSFXSR[bit 9] = 0. (128-bit operations only) If CPUID.01H:EDX.SSE2[bit 26] = 0. If the LOCK prefix is used.
#GP(0) If the memory address is in a non-canonical form. (128-bit operations only) If memory operand is not aligned on a 16-byte boundary, regardless of segment.
#SS(0) If a memory address referencing the SS segment is in a non-canonical form.

Compatibility Mode Exceptions

Same as for protected mode exceptions.

Virtual-8086 Mode Exceptions

Exception Description
#AC(0) (64-bit operations only) If alignment checking is enabled and an unaligned memory reference is made.
#PF(fault-code) For a page fault.
Same exceptions as in real address mode.

Real-Address Mode Exceptions

Exception Description
#MF (64-bit operations only) If there is a pending x87 FPU exception.
#NM If CR0.TS[bit 3] = 1.
#UD If CR0.EM[bit 2] = 1. 128-bit operations will generate #UD only if CR4.OSFXSR[bit 9] = 0. Execution of 128-bit instructions on a non-SSE2 capable processor (one that is MMX technology capable) will result in the instruction operating on the mm registers, not #UD. If the LOCK prefix is used.
#GP (128-bit operations only) If a memory operand is not aligned on a 16-byte boundary, regardless of segment. If any part of the operand lies outside of the effective address space from 0 to FFFFH.

Protected Mode Exceptions

Exception Description
#AC(0) (64-bit operations only) If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3.
#PF(fault-code) If a page fault occurs.
#MF (64-bit operations only) If there is a pending x87 FPU exception.
#NM If CR0.TS[bit 3] = 1.
#UD If CR0.EM[bit 2] = 1. 128-bit operations will generate #UD only if CR4.OSFXSR[bit 9] = 0. Execution of 128-bit instructions on a non-SSE2 capable processor (one that is MMX technology capable) will result in the instruction operating on the mm registers, not #UD. If the LOCK prefix is used.
#SS(0) If a memory operand effective address is outside the SS segment limit.
#GP(0) If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit. (128-bit operations only) If a memory operand is not aligned on a 16-byte boundary, regardless of segment.