# _mm_fmadd_pd, _mm256_fmadd_pd

Multiply-adds packed double-precision floating-point values using three float64 vectors. The corresponding FMA instruction is VFMADD<XXX>PD, where XXX could be 132, 213, or 231.

## Syntax

For 128-bit vector

extern __m128d _mm_fmadd_pd(__m128d a, __m128d b, __m128d c);

For 256-bit vector

extern __m256d _mm256_fmadd_pd(__m256d a, __m256d b, __m256d c);

## Arguments

a | float64 vector used for the operation
b | float64 vector also used for the operation
c | float64 vector also used for the operation

## Description

Performs a set of SIMD multiply-add computation on packed double-precision floating-point values using three source vectors/operands, `a`,`b`, and `c`. Corresponding values in two operands, `a` and `b`, are multiplied and the infinite precision intermediate results are added to corresponding values in the third operand, after which the final results are rounded to the nearest float64 values.

The compiler defaults to using the VFMADD213PD instruction and uses the other forms VFMADD132PD or VFMADD231PD only if a low level optimization decides it is useful or necessary. For example, the compiler could change the default if it finds that another instruction form saves a register or eliminates a move.

## Returns

Result of the multiply-add operation.

Parent topic: Intrinsics for Fused Multiply Add Operations