PCMPEQB/PCMPEQW/PCMPEQD— Compare Packed Data for Equal

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

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

Flags Affected

None.

SIMD Floating-Point Exceptions

None.

Other Exceptions

See Exceptions Type 4; additionally