Intel® C++ Compiler Classic Developer Guide and Reference

ID 767249
Date 12/16/2022
Public

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<span class='option'> _mm_fmsub_pd, _mm256_fmsub_pd</span>

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

Syntax

For 128-bit vector

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

For 256-bit vector

extern __m256d _mm256_fmsub_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-subtract 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 obtained. From the infinite precision intermediate results, the values in the third operand, c, are subtracted. The final results are rounded to the nearest float64 values.

The compiler defaults to using the VFMSUB213PD instruction and uses the other forms VFMSUB132PD or VFMSUB231PD 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.