# _mm_fmsub_sd

Multiply-subtracts scalar double-precision floating-point values using three float64 vectors. The corresponding FMA instruction is VFMSUB<XXX>SD, where XXX could be 132, 213, or 231.

## Syntax

extern __m128d _mm_fmsub_sd(__m128d a, __m128d b, __m128d 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 scalar SIMD multiply-subtract computation on scalar double-precision floating-point values in the low 64-bits of three source operands, a, b, and c. The float64 values in two operands, a and b, are multiplied and the infinite precision intermediate result is obtained. From the infinite precision intermediate result, the float64 value in the third operand, c, is subtracted. The final result is rounded to the nearest float64 value.

The compiler defaults to using the VFMSUB213SD instruction and uses the other forms VFMSUB132SD or VFMSUB231SD only if a low level optimization decides it is useful/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-subtract operation.

Parent topic: Intrinsics for Fused Multiply Add Operations