PEXT — Parallel Bits Extract

Opcode/Instruction Op/En 64/32 -bit Mode CPUID Feature Flag Description

VEX.NDS.LZ.F3.0F38.W0 F5 /r

PEXT r32a, r32b, r/m32

 RVM V/V BMI2 Parallel extract of bits from r32b using mask in r/m32, result is writ-ten to r32a.

VEX.NDS.LZ.F3.0F38.W1 F5 /r

PEXT r64a, r64b, r/m64

 RVM V/N.E. BMI2 Parallel extract of bits from r64b using mask in r/m64, result is writ-ten to r64a.

Instruction Operand Encoding

Op/En Operand 1 Operand 2 Operand 3 Operand 4
RVM ModRM:reg (w) VEX.vvvv (r) ModRM:r/m (r) NA

Description

PEXT uses a mask in the second source operand (the third operand) to transfer either contiguous or non-contig-uous bits in the first source operand (the second operand) to contiguous low order bit positions in the destination (the first operand). For each bit set in the MASK, PEXT extracts the corresponding bits from the first source operand and writes them into contiguous lower bits of destination operand. The remaining upper bits of destination are zeroed.

SRC1

S31 S30 S29 S28 S27

S7

S6

S5

S4

S3

S2

S1

S0

SRC2

0

0

0

0

1

0

1

0

1

0

1

0

0

(mask)

S2

0

0

0

0

0

0

0

0

0

S7

S5

DEST

S28

bit 0

bit 31

Figure 4-5. PEXT Example

This instruction is not supported in real mode and virtual-8086 mode. The operand size is always 32 bits if not in 64-bit mode. In 64-bit mode operand size 64 requires VEX.W1. VEX.W1 is ignored in non-64-bit modes. An attempt to execute this instruction with VEX.L not equal to 0 will cause #UD.

Operation

TEMP ← SRC1;
MASK ← SRC2;
DEST ← 0 ;
m← 0, k← 0;
DO WHILE m< OperandSize
         IF MASK[ m] = 1 THEN
              DEST[ k] ← TEMP[ m];
              k ← k+ 1;
         FI
         m ← m+ 1;
OD

Flags Affected

None.

Intel C/C++ Compiler Intrinsic Equivalent

PEXT:

unsigned __int32 _pext_u32(unsigned __int32 src, unsigned __int32 mask);

PEXT:

unsigned __int64 _pext_u64(unsigned __int64 src, unsigned __int32 mask);

SIMD Floating-Point Exceptions

None

Other Exceptions

See Section 2.5.1, “Exception Conditions for VEX-Encoded GPR Instructions”, Table 2-29; additionally

#UD If VEX.W = 1.