# PCMPISTRM — Packed Compare Implicit Length Strings, Return Mask

Opcode/Instruction | Op/En | 64/32 bit Mode Support | CPUID Feature Flag | Description
--- | --- | --- | --- | ---
66 0F 3A 62 /r imm8 PCMPISTRM xmm1, xmm2/m128, imm8 | RM | V/V | SSE4_2 | Perform a packed comparison of string data with implicit lengths, generating a mask, and storing the result in XMM0.
VEX.128.66.0F3A.WIG 62 /r ib VPCMPISTRM xmm1, xmm2/m128, imm8 | RM | V/V | AVX | Perform a packed comparison of string data with implicit lengths, generating a Mask, and storing the result in XMM0.

## Instruction Operand Encoding ¶

Op/En | Operand 1 | Operand 2 | Operand 3 | Operand 4
--- | --- | --- | --- | ---
RM | ModRM:reg (r) | ModRM:r/m (r) | imm8 | N/A

## Description ¶

The instruction compares data from two strings based on the encoded value in the imm8 byte (see Section 4.1, “Imm8 Control Byte Operation for PCMPESTRI / PCMPESTRM / PCMPISTRI / PCMPISTRM”) generating a mask stored to XMM0.

Each string is represented by a single value. The value is an xmm (or possibly m128 for the second operand) which contains the data elements of the string (byte or word data). Each input byte/word is augmented with a valid/invalid tag. A byte/word is considered valid only if it has a lower index than the least significant null byte/word. (The least significant null byte/word is also considered invalid.)

The comparison and aggregation operation are performed according to the encoded value of imm8 bit fields (see Section 4.1). As defined by imm8[6], IntRes2 is then either stored to the least significant bits of XMM0 (zero extended to 128 bits) or expanded into a byte/word-mask and then stored to XMM0.

Note that the Arithmetic Flags are written in a non-standard manner in order to supply the most relevant information:

CFlag – Reset if IntRes2 is equal to zero, set otherwise

ZFlag – Set if any byte/word of xmm2/mem128 is null, reset otherwise

SFlag – Set if any byte/word of xmm1 is null, reset otherwise

OFlag – IntRes2[0]

AFlag – Reset

PFlag – Reset

Note: In VEX.128 encoded versions, bits (MAXVL-1:128) of XMM0 are zeroed. VEX.vvvv is reserved and must be 1111b, VEX.L must be 0, otherwise the instruction will #UD.

## Effective Operand Size ¶

Operating mode/size | Operand 1 | Operand 2 | Result
--- | --- | --- | ---
16 bit | xmm | xmm/m128 | XMM0
32 bit | xmm | xmm/m128 | XMM0
64 bit | xmm | xmm/m128 | XMM0

## Intel C/C++ Compiler Intrinsic Equivalent For Returning Mask ¶

__m128i _mm_cmpistrm (__m128i a, __m128i b, const int mode);

## Intel C/C++ Compiler Intrinsics For Reading EFlag Results ¶

int _mm_cmpistra (__m128i a, __m128i b, const int mode);

int _mm_cmpistrc (__m128i a, __m128i b, const int mode);

int _mm_cmpistro (__m128i a, __m128i b, const int mode);

int _mm_cmpistrs (__m128i a, __m128i b, const int mode);

int _mm_cmpistrz (__m128i a, __m128i b, const int mode);

## SIMD Floating-Point Exceptions ¶

None.

## Other Exceptions ¶

See Table 2-21, “Type 4 Class Exception Conditions,” additionally, this instruction does not cause #GP if the memory operand is not aligned to 16 Byte boundary, and:

#UD | If VEX.L = 1.
If VEX.vvvv ≠ 1111B.