PCMPEQB/PCMPEQW/PCMPEQD (Compare Packed Data for Equal)

Opcodes

Opcode/Instruction Op/En 64/32 bit Mode Support CPUID Feature Flag Description
0F 74 /r1 PCMPEQB mm, mm/m64 RM V/V MMX Compare packed bytes in mm/m64 and mm for equality.
66 0F 74 /r PCMPEQB xmm1, xmm2/m128 RM V/V SSE2 Compare packed bytes in xmm2/m128 and xmm1 for equality.
0F 75 /r1 PCMPEQW mm, mm/m64 RM V/V MMX Compare packed words in mm/m64 and mm for equality.
66 0F 75 /r PCMPEQW xmm1, xmm2/m128 RM V/V SSE2 Compare packed words in xmm2/m128 and xmm1 for equality.
0F 76 /r1 PCMPEQD mm, mm/m64 RM V/V MMX Compare packed doublewords in mm/m64 and mm for equality.
66 0F 76 /r PCMPEQD xmm1, xmm2/m128 RM V/V SSE2 Compare packed doublewords in xmm2/m128 and xmm1 for equality.
VEX.NDS.128.66.0F.WIG 74 /r VPCMPEQB xmm1, xmm2, xmm3/m128 RVM V/V AVX Compare packed bytes in xmm3/m128 and xmm2 for equality.
VEX.NDS.128.66.0F.WIG 75 /r VPCMPEQW xmm1, xmm2, xmm3/m128 RVM V/V AVX Compare packed words in xmm3/m128 and xmm2 for equality.
VEX.NDS.128.66.0F.WIG 76 /r VPCMPEQD xmm1, xmm2, xmm3/m128 RVM V/V AVX Compare packed doublewords in xmm3/m128 and xmm2 for equality.
VEX.NDS.256.66.0F.WIG 74 /r VPCMPEQB ymm1, ymm2, ymm3 /m256 RVM V/V AVX2 Compare packed bytes in ymm3/m256 and ymm2 for equality.
VEX.NDS.256.66.0F.WIG 75 /r VPCMPEQW ymm1, ymm2, ymm3 /m256 RVM V/V AVX2 Compare packed words in ymm3/m256 and ymm2 for equality.
VEX.NDS.256.66.0F.WIG 76 /r VPCMPEQD ymm1, ymm2, ymm3 /m256 RVM V/V AVX2 Compare packed doublewords in ymm3/m256 and ymm2 for equality.

NOTES:

1. See note in Section 2.4, “Instruction Exception Specification” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A and Section 22.25.3, “Exception Conditions of Legacy SIMD Instructions Operating on MMX Registers” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A.

Instruction Operand Encoding

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

Description

Performs a SIMD compare for equality of the packed bytes, words, or doublewords in the destination operand (first operand) and the source operand (second operand). If a pair of data elements is equal, the corresponding data element in the destination operand is set to all 1s; otherwise, it is set to all 0s.

The (V)PCMPEQB instruction compares the corresponding bytes in the destination and source operands; the (V)PCMPEQW instruction compares the corresponding words in the destination and source operands; and the (V)PCMPEQD instruction compares the corresponding doublewords in the destination and source operands.

In 64-bit mode, using a REX prefix in the form of REX.R permits this instruction to access additional registers (XMM8-XMM15).

Legacy SSE instructions: The source operand can be an MMX technology register or a 64-bit memory location. The destination operand can be an MMX technology register.

128-bit Legacy SSE version: The second source operand can be an XMM register or a 128-bit memory location. The first source and destination operands are XMM registers. Bits (VLMAX-1:128) of the corresponding YMM destination register remain unchanged.

VEX.128 encoded version: The second source operand can be an XMM register or a 128-bit memory location. The first source and destination operands are XMM registers. Bits (VLMAX-1:128) of the corresponding YMM register are zeroed.

VEX.256 encoded version: The first source operand is a YMM register. The second source operand is a YMM register or a 256-bit memory location. The destination operand is a YMM register.

Note: VEX.L must be 0, otherwise the instruction will #UD.

Operation

PCMPEQB (with 64-bit operands)

    IF DEST[7:0] = SRC[7:0]
         THEN DEST[7:0) ← FFH;
         ELSE DEST[7:0] ← 0; FI;
    (* Continue comparison of 2nd through 7th bytes in DEST and SRC *)
    IF DEST[63:56] = SRC[63:56]
         THEN DEST[63:56] ← FFH;
         ELSE DEST[63:56] ← 0; FI;

PCMPEQB (with 128-bit operands)

    IF DEST[7:0] = SRC[7:0]
         THEN DEST[7:0) ← FFH;
         ELSE DEST[7:0] ← 0; FI;
    (* Continue comparison of 2nd through 15th bytes in DEST and SRC *)
    IF DEST[127:120] = SRC[127:120]
         THEN DEST[127:120] ← FFH;
         ELSE DEST[127:120] ← 0; FI;

VPCMPEQB (VEX.128 encoded version)

DEST[127:0] ←COMPARE_BYTES_EQUAL(SRC1[127:0],SRC2[127:0])
DEST[VLMAX-1:128] ← 0

VPCMPEQB (VEX.256 encoded version)

DEST[127:0] ←COMPARE_BYTES_EQUAL(SRC1[127:0],SRC2[127:0])
DEST[255:128] ←COMPARE_BYTES_EQUAL(SRC1[255:128],SRC2[255:128])

PCMPEQW (with 64-bit operands)

    IF DEST[15:0] = SRC[15:0]
         THEN DEST[15:0] ← FFFFH;
         ELSE DEST[15:0] ← 0; FI;
    (* Continue comparison of 2nd and 3rd words in DEST and SRC *)
    IF DEST[63:48] = SRC[63:48]
         THEN DEST[63:48] ← FFFFH;
         ELSE DEST[63:48] ← 0; FI;

PCMPEQW (with 128-bit operands)

    IF DEST[15:0] = SRC[15:0]
         THEN DEST[15:0] ← FFFFH;
         ELSE DEST[15:0] ← 0; FI;
    (* Continue comparison of 2nd through 7th words in DEST and SRC *)
    IF DEST[127:112] = SRC[127:112]
         THEN DEST[127:112] ← FFFFH;
         ELSE DEST[127:112] ← 0; FI;

VPCMPEQW (VEX.128 encoded version)

DEST[127:0] ←COMPARE_WORDS_EQUAL(SRC1[127:0],SRC2[127:0])
DEST[VLMAX-1:128] ← 0

VPCMPEQW (VEX.256 encoded version)

DEST[127:0] ←COMPARE_WORDS_EQUAL(SRC1[127:0],SRC2[127:0])
DEST[255:128] ←COMPARE_WORDS_EQUAL(SRC1[255:128],SRC2[255:128])

PCMPEQD (with 64-bit operands)

    IF DEST[31:0] = SRC[31:0]
         THEN DEST[31:0] ← FFFFFFFFH;
         ELSE DEST[31:0] ← 0; FI;
    IF DEST[63:32] = SRC[63:32]
         THEN DEST[63:32] ← FFFFFFFFH;
         ELSE DEST[63:32] ← 0; FI;

PCMPEQD (with 128-bit operands)

    IF DEST[31:0] = SRC[31:0]
         THEN DEST[31:0] ← FFFFFFFFH;
         ELSE DEST[31:0] ← 0; FI;
    (* Continue comparison of 2nd and 3rd doublewords in DEST and SRC *)
    IF DEST[127:96] = SRC[127:96]
         THEN DEST[127:96] ← FFFFFFFFH;
         ELSE DEST[127:96] ← 0; FI;

VPCMPEQD (VEX.128 encoded version)

DEST[127:0] ←COMPARE_DWORDS_EQUAL(SRC1[127:0],SRC2[127:0])
DEST[VLMAX-1:128] ← 0

VPCMPEQD (VEX.256 encoded version)

DEST[127:0] ←COMPARE_DWORDS_EQUAL(SRC1[127:0],SRC2[127:0])
DEST[255:128] ←COMPARE_DWORDS_EQUAL(SRC1[255:128],SRC2[255:128])

Intel C/C++ Compiler Intrinsic Equivalents

PCMPEQB:

__m64 _mm_cmpeq_pi8 (__m64 m1, __m64 m2)

PCMPEQW:

__m64 _mm_cmpeq_pi16 (__m64 m1, __m64 m2)

PCMPEQD:

__m64 _mm_cmpeq_pi32 (__m64 m1, __m64 m2)

(V)PCMPEQB:

__m128i _mm_cmpeq_epi8 ( __m128i a, __m128i b)

(V)PCMPEQW:

__m128i _mm_cmpeq_epi16 ( __m128i a, __m128i b)

(V)PCMPEQD:

__m128i _mm_cmpeq_epi32 ( __m128i a, __m128i b)

VPCMPEQB:

__m256i _mm256_cmpeq_epi8 ( __m256i a, __m256i b)

VPCMPEQW:

__m256i _mm256_cmpeq_epi16 ( __m256i a, __m256i b)

VPCMPEQD:

__m256i _mm256_cmpeq_epi32 ( __m256i a, __m256i b)

Flags Affected

None.

SIMD Floating-Point Exceptions

None.

Other Exceptions

See Exceptions Type 4; additionally

#UD If VEX.L = 1.