Developer Guide and Reference

Contents

_mm_fmsubadd_ps, _mm256_fmsubadd_ps

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

Syntax

For 128-bit vector
extern __m128 _mm_fmsubadd_ps(__m128 a, __m128 b, __m128 c);
For 256-bit vector
extern __m256 _mm256_fmsubadd_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-add 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 infinite precision intermediate results are obtained. The odd values in the third operand,
c
, are subtracted from the intermediate results while the even values are added to them. The final results are rounded to the nearest float32 values.
The compiler defaults to using the
VFMSUBADD213PS
instruction and uses the other forms
VFMSUBADD132PS
or
VFMSUBADDS231PS
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-add-subtract operation.