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

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

2. 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.

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:

VPEXTRTD/VPEXTRQ ¶

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

VPEXTRB ( dest=m8) ¶

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

VPEXTRB ( dest=reg) ¶

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

EVEX-encoded instruction, see Exceptions Type E9NF.