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Microsoft Specific
Generates the extrq instruction to extract specified bits from the low 64 bits of its first argument.
__m128i _mm_extract_si64(
__m128i Source,
__m128i Descriptor
);
__m128i _mm_extracti_si64(
__m128i Source,
int Length,
int Index
);
Parameters
[in] Source
A 128-bit field with input data in its lower 64 bits.[in] Descriptor
A 128-bit field that describes the bit field to extract.[in] Length
An integer that specifies the length of the field to extract.[in] Index
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
This intrinsic generates the extrq instruction to extract bits from Source.There are two versions of this intrinsic: _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, thus 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 cannot 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 does not 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
Copyright 2007 by Advanced Micro Devices, Inc. All rights reserved. Reproduced with permission from Advanced Micro Devices, Inc.