PEXTRB/PEXTRD/PEXTRQ — Extract Byte/Dword/Qword

NOTES:

1. In 64-bit mode, VEX.W1 is ignored for VPEXTRB (similar to legacy REX.W=1 prefix in PEXTRB).

NOTES: 1. VEX.W/EVEX.W in non-64 bit is ignored; the instructions behaves as if the W0 version is used.

Instruction Operand Encoding

Description

Extract a byte/dword/qword integer value from the source XMM register at a byte/dword/qword offset determined from imm8[3:0]. The destination can be a register or byte/dword/qword memory location. If the destination is a register, the upper bits of the register are zero extended.

In legacy non-VEX encoded version and if the destination operand is a register, the default operand size in 64-bit mode for PEXTRB/PEXTRD is 64 bits, the bits above the least significant byte/dword data are filled with zeros. PEXTRQ is not encodable in non-64-bit modes and requires REX.W in 64-bit mode.

Note: In VEX.128 encoded versions, VEX.vvvv is reserved and must be 1111b, VEX.L must be 0, otherwise the instruction will #UD. In EVEX.128 encoded versions, EVEX.vvvv is reserved and must be 1111b, EVEX.L”L must be 0, otherwise the instruction will #UD. If the destination operand is a register, the default operand size in 64-bit mode for VPEXTRB/VPEXTRD is 64 bits, the bits above the least significant byte/word/dword data are filled with zeros. Attempt to execute VPEXTRQ in non-64-bit mode will cause #UD.

Operation

CASE of
PEXTRB: SEL (cid:197) COUNT[3:0];
TEMP (cid:197) (Src >> SEL*8) AND FFH;
IF (DEST = Mem8)
    THEN
    Mem8 (cid:197) TEMP[7:0];
    ELSE IF (64-Bit Mode and 64-bit register selected)
    THEN
    R64[7:0] (cid:197) TEMP[7:0]; r64[63:8] ← ZERO_FILL; };
ELSE
R32[7:0] (cid:197) TEMP[7:0]; r32[31:8] ← ZERO_FILL; };
FI;
PEXTRD:SEL (cid:197) COUNT[1:0];
TEMP (cid:197) (Src >> SEL*32) AND FFFF_FFFFH;
DEST (cid:197) TEMP;
PEXTRQ: SEL (cid:197) COUNT[0];
TEMP (cid:197) (Src >> SEL*64);
DEST (cid:197) TEMP;
EASC:

IF (64-Bit Mode and 64-bit dest operand)
    THEN
    Src_Offset (cid:197) Imm8[0]
    r64/m64 (cid:197)(Src >> Src_Offset * 64)
    ELSE
    Src_Offset (cid:197) Imm8[1:0]
    r32/m32 (cid:197) ((Src >> Src_Offset *32) AND 0FFFFFFFFh);
FI

SRC_Offset (cid:197) Imm8[3:0]
Mem8 (cid:197) (Src >> Src_Offset*8)

IF (64-Bit Mode )
    THEN
    SRC_Offset (cid:197) Imm8[3:0]
    DEST[7:0] (cid:197) ((Src >> Src_Offset*8) AND 0FFh)
    DEST[63:8] (cid:197)(cid:3)ZERO_FILL;
ELSE
SRC_Offset (cid:197). Imm8[3:0];
DEST[7:0] (cid:197) ((Src >> Src_Offset*8) AND 0FFh);
DEST[31:8] (cid:197)(cid:3)ZERO_FILL;
FI

Intel C/C++ Compiler Intrinsic Equivalent

PEXTRB:
int _mm_extract_epi8 (__m128i src, const int ndx);
PEXTRD:
int _mm_extract_epi32 (__m128i src, const int ndx);
PEXTRQ:
__int64 _mm_extract_epi64 (__m128i src, const int ndx);

Flags Affected

None.

SIMD Floating-Point Exceptions

None.

Other Exceptions

Non-EVEX-encoded instruction, see Exceptions Type 5;