Developer Guide and Reference

Contents

_mm_fmsub_pd, _mm256_fmsub_pd

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.

Product and Performance Information

1

Intel's compilers may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice.

Notice revision #20110804