PCLMULQDQ — Carry-Less Multiplication Quadword

Opcode/Instruction	Op/En	64/32 bit Mode Support	CPUID Feature Flag	Description
66 0F 3A 44 /r ib PCLMULQDQ xmm1, xmm2/m128, imm8	RMI	V/V	PCLMULQDQ	Carry-less multiplication of one quadword of xmm1 by one quadword of xmm2/m128, stores the 128-bit result in xmm1. The immediate is used to determine which quadwords of xmm1 and xmm2/m128 should be used.
VEX.NDS.128.66.0F3A.WIG 44 /r ib VPCLMULQDQ xmm1, xmm2, xmm3/m128, imm8	RVMI	V/V	Both PCLMULQDQ and AVX flags	Carry-less multiplication of one quadword of xmm2 by one quadword of xmm3/m128, stores the 128-bit result in xmm1. The immediate is used to determine which quadwords of xmm2 and xmm3/m128 should be used.

Instruction Operand Encoding ¶

Op/En	Operand 1	Operand2	Operand3	Operand4
RMI	ModRM:reg (r, w)	ModRM:r/m (r)	imm8	NA
RVMI	ModRM:reg (w)	VEX.vvvv (r)	ModRM:r/m (r)	imm8

Description ¶

Performs a carry-less multiplication of two quadwords, selected from the first source and second source operand according to the value of the immediate byte. Bits 4 and 0 are used to select which 64-bit half of each operand to use according to Table 4-13, other bits of the immediate byte are ignored.

Imm[4]	Imm[0]	PCLMULQDQ Operation
0	0	CL_MUL( SRC2¹[63:0], SRC1[63:0] )
0	1	CL_MUL( SRC2[63:0], SRC1[127:64] )
1	0	CL_MUL( SRC2[127:64], SRC1[63:0] )
1	1	CL_MUL( SRC2[127:64], SRC1[127:64] )

Table 4-13. PCLMULQDQ Quadword Selection of Immediate Byte

1. SRC2 denotes the second source operand, which can be a register or memory; SRC1 denotes the first source and destination operand.

The first source operand and the destination operand are the same and must be an XMM register. The second source operand can be an XMM register or a 128-bit memory location. Bits (MAXVL-1:128) of the corresponding YMM destination register remain unchanged.

Compilers and assemblers may implement the following pseudo-op syntax to simply programming and emit the required encoding for Imm8.

Pseudo-Op	Imm8 Encoding
PCLMULLQLQDQ xmm1, xmm2	0000_0000B
PCLMULHQLQDQ xmm1, xmm2	0000_0001B
PCLMULLQHQDQ xmm1, xmm2	0001_0000B
PCLMULHQHQDQ xmm1, xmm2	0001_0001B

Table 4-14. Pseudo-Op and PCLMULQDQ Implementation

Operation ¶

PCLMULQDQ ¶

IF (Imm8[0] = 0 )
    THEN
        TEMP1←SRC1 [63:0];
    ELSE
        TEMP1←SRC1 [127:64];
FI
IF (Imm8[4] = 0 )
    THEN
        TEMP2←SRC2 [63:0];
    ELSE
        TEMP2←SRC2 [127:64];
FI
For i = 0 to 63 {
    TmpB [ i ]←(TEMP1[ 0 ] and TEMP2[ i ]);
    For j = 1 to i {
        TmpB [ i ]←TmpB [ i ] xor (TEMP1[ j ] and TEMP2[ i - j ])
    }
    DEST[ i ]←TmpB[ i ];
}
For i = 64 to 126 {
    TmpB [ i ]←0;
    For j = i - 63 to 63 {
        TmpB [ i ]←TmpB [ i ] xor (TEMP1[ j ] and TEMP2[ i - j ])
    }
    DEST[ i ]←TmpB[ i ];
}
DEST[127] ← 0;
DEST[MAXVL-1:128] (Unmodified)

VPCLMULQDQ ¶

IF (Imm8[0] = 0 )
    THEN
        TEMP1←SRC1 [63:0];
    ELSE
        TEMP1←SRC1 [127:64];
FI
IF (Imm8[4] = 0 )
    THEN
        TEMP2←SRC2 [63:0];
    ELSE
        TEMP2←SRC2 [127:64];
FI
For i = 0 to 63 {
    TmpB [ i ]←(TEMP1[ 0 ] and TEMP2[ i ]);
    For j = 1 to i {
        TmpB [i]←TmpB [i] xor (TEMP1[ j ] and TEMP2[ i - j ])
    }
    DEST[i] ← TmpB[i];
}
For i = 64 to 126 {
    TmpB [ i ]←0;
    For j = i - 63 to 63 {
        TmpB [i]←TmpB [i] xor (TEMP1[ j ] and TEMP2[ i - j ])
    }
    DEST[i] ← TmpB[i];
}
DEST[MAXVL-1:127] ← 0;

Intel C/C++ Compiler Intrinsic Equivalent ¶

(V)PCLMULQDQ: __m128i _mm_clmulepi64_si128 (__m128i, __m128i, const int)

SIMD Floating-Point Exceptions ¶

None.

Other Exceptions ¶

See Exceptions Type 4, additionally

#UD	If VEX.L = 1.