The __m128 data type, for use with the Streaming SIMD Extensions and Streaming SIMD Extensions 2 instructions intrinsics, is defined in <xmmintrin.h>.

// data_types__m128.cpp
#include <xmmintrin.h>
int main() {
   __m128 x;
}

You should not access the __m128 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 __m128 are automatically aligned on 16-byte boundaries.

The __m128 data type is not supported on ARM processors.

END Microsoft Specific

Keywords
Fundamental Types
Data Type Ranges