_mm_extract_si64, _mm_extracti_si64

Article
08/03/2021

Microsoft Specific

Generates the extrq instruction to extract specified bits from the low 64 bits of its first argument.

Syntax

__m128i _mm_extract_si64(
   __m128i Source,
   __m128i Descriptor
);
__m128i _mm_extracti_si64(
   __m128i Source,
   int Length,
   int Index
);

Parameters

Source
[in] A 128-bit field with input data in its lower 64 bits.

Descriptor
[in] A 128-bit field that describes the bit field to extract.

Length
[in] An integer that specifies the length of the field to extract.

Index
[in] An integer that specifies the index of the field to extract

Return value

A 128-bit field with the extracted field in its least significant bits.

Requirements

Intrinsic	Architecture
`_mm_extract_si64`	SSE4a
`_mm_extracti_si64`	SSE4a

Header file <intrin.h>

Remarks

These intrinsics generate the extrq instruction to extract bits from Source. There are two versions: _mm_extracti_si64 is the immediate version, and _mm_extract_si64 is the non-immediate one. Each version extracts from Source a bit field defined by its length and the index of its least significant bit. The values of the length and index are taken mod 64, so both -1 and 127 are interpreted as 63. If the sum of the (reduced) index and (reduced) field length is greater than 64, the results are undefined. A value of zero for field length is interpreted as 64. If the field length and bit index are both zero, bits 63:0 of Source are extracted. If the field length is zero but the bit index is non-zero, the results are undefined.

In a call to _mm_extract_si64, the Descriptor contains the index in bits 13:8 and the field length of the data to be extracted in bits 5:0.

If you call _mm_extracti_si64 with arguments that the compiler can't determine to be integer constants, the compiler generates code to pack those values into an XMM register (Descriptor) and to call _mm_extract_si64.

To determine hardware support for the extrq instruction, call the __cpuid intrinsic with InfoType=0x80000001 and check bit 6 of CPUInfo[2] (ECX). This bit will be 1 if the instruction is supported, and 0 otherwise. If you run code that uses this intrinsic hardware that doesn't support the extrq instruction, the results are unpredictable.

Example

// Compile this sample with: /EHsc
#include <iostream>
#include <intrin.h>
using namespace std;

union {
    __m128i m;
    unsigned __int64 ui64[2];
} source, descriptor, result1, result2, result3;

int
main()
{
    source.ui64[0] =     0xfedcba9876543210ll;
    descriptor.ui64[0] = 0x0000000000000b1bll;

    result1.m = _mm_extract_si64 (source.m, descriptor.m);
    result2.m = _mm_extracti_si64(source.m, 27, 11);
    result3.ui64[0] = (source.ui64[0] >> 11) & 0x7ffffff;

    cout << hex << "result1 = 0x" << result1.ui64[0] << endl;
    cout << "result2 = 0x" << result2.ui64[0] << endl;
    cout << "result3 = 0x" << result3.ui64[0] << endl;
}

result1 = 0x30eca86
result2 = 0x30eca86
result3 = 0x30eca86

END Microsoft Specific

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