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).

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

(V)PEXTRTD/(V)PEXTRQ

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

(V)PEXTRB ( dest=m8)

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

(V)PEXTRB ( dest=reg)

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

See Exceptions Type 5; additionally