# _mm256_castpd256_pd128

Typecasts 256-bit double-precision floating point values to 128-bit double-precision floating point values. No corresponding Intel® AVX instruction.

## Syntax

extern __m128d _mm256_castpd256_pd128(__m256d a);

## Arguments

a | 256-bit float64 source vector

## Description

Performs a typecast operation from 256-bit double-precision floating point values to 128-bit double-precision floating point values.

The lower 128-bits of the source vector are passed unchanged to the result. This intrinsic does not introduce extra moves to the generated code.

## Returns

A vector with 128-bit double-precision floating point values.

Parent topic: Support Intrinsics for Vector Typecasting Operations