# _mm_fnmsub_sd

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

## Syntax

extern __m128d _mm_fnmsub_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 negated 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 negated infinite precision intermediate result is obtained. From this negated 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 VFNMSUB213SD instruction and uses the other forms VFNMSUB132SD or VFNMSUB231SD 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 negated multiply-subtract operation.

Parent topic: Intrinsics for Fused Multiply Add Operations