Intel® C++ Compiler Classic Developer Guide and Reference

ID 767249
Date 3/31/2023
Public

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_mm_fmsub_ps, _mm256_fmsub_ps

Multiply-subtracts packed single-precision floating-point values using three float32 vectors. The corresponding FMA instruction is VFMSUB<XXX>PS, where XXX could be 132, 213, or 231.

Syntax

For 128-bit vector

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

For 256-bit vector

extern __m256 _mm256_fmsub_ps(__m256 a, __m256 b, __m256 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 SIMD multiply-subtract computation on packed single-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 obtained. From the infinite precision intermediate results, the values in the third operand, c, are subtracted. The final results are rounded to the nearest float32 values.

The compiler defaults to using the VFMSUB213PS instruction and uses the other forms VFMSUB132PS or VFMSUB231PS 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-subtract operation.