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The __m128d data type, for use with the Streaming SIMD Extensions 2 instructions intrinsics, is defined in emmintrin.h.

// data_types__m128d.cpp
#include <emmintrin.h>
int main() {
   __m128d x;

You should not access the __m128d fields directly. You can, however, see these types in the debugger. A variable of type __m128 maps to the XMM[0-7] registers.

Variables of type _m128d are automatically aligned on 16-byte boundaries.

The __m128d data type is not supported on Itanium Processor Family (IPF) processors.

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