Intel® C++ Compiler Classic Developer Guide and Reference

ID 767249
Date 12/16/2022
Public

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<span class='option'> _mm_fmsub_ss </span>

Multiply-subtracts scalar single-precision floating-point values using three float32vectors. The corresponding FMA instruction is VFMSUB<XXX>SS, where XXX could be 132, 213, or 231.

Syntax

extern __m128 _mm_fmsub_ss(__m128 a, __m128 b, __m128 c);

Arguments

a

float32 vector used for the operation

b

float32 vector also used for the operation

c

float32 vector also used for the operation

Description

Performs a set of scalar SIMD multiply-subtract computation on scalar single-precision floating-point values in the low 32-bits of three source operands, a, b, and c. The float32 values in two operands, a and b, are multiplied and the infinite precision intermediate result is obtained. From the infinite precision intermediate result, the float32 value in the third operand, c, is subtracted. The final result is rounded to the nearest float32 value.

The compiler defaults to using the VFMSUB213SS instruction and uses the other forms VFMSUB132SS or VFMSUB231SS 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.