_mm_maddsub_ps
Visual Studio 2010 SP1 is required.
Microsoft Specific
Generates the FMA4 XMM instruction vfmaddsubps to perform an alternating single-round floating-point multiply-add/subtract of its sources.
__m128 _mm_maddsub_ps (
__m128 src1,
__m128 src2,
__m128 src3
);
Parameters
[in] src1
A 128-bit parameter that contains four 32-bit floating-point values.[in] src2
A 128-bit parameter that contains four 32-bit floating-point values.[in] src3
A 128-bit parameter that contains four 32-bit floating-point values.
Return value
A 128-bit result r that contains four 32-bit floating-point values.
r[i] := src1[i] * src2[i] - src3[i]; // i even
r[i] := src1[i] * src2[i] + src3[i]; // i odd
Requirements
Intrinsic |
Architecture |
|---|---|
_mm_maddsub_ps |
FMA4 |
Header file <intrin.h>
Remarks
Each of the four single-precision floating-point values in src1 is multiplied by the corresponding value in src2. Each even-numbered source value of src3 is subtracted from its corresponding product, each odd-numbered value is added to its corresponding product, and each result is stored as the corresponding value in the destination. Each multiply-add/subtract pair is performed with a single round at the end, as if intermediate results were computed to infinite precision.
The vfmaddsubps instruction is part of the FMA4 family of instructions. Before you use this intrinsic, you must ensure that the processor supports this instruction. To determine hardware support for this instruction, call the __cpuid intrinsic with InfoType = 0x80000001 and check bit 16 of CPUInfo[2] (ECX). This bit is 1 when the instruction is supported, and 0 otherwise.
Example
#include <stdio.h>
#include <intrin.h>
int main()
{
__m128 a, b, c, d;
int i;
for (i = 0; i < 4; i++) {
a.m128_f32[i] = i;
b.m128_f32[i] = 2.;
c.m128_f32[i] = 3.;
}
d = _mm_maddsub_ps(a, b, c);
for (i = 0; i < 4; i++) printf_s(" %.3f", d.m128_f32[i]);
printf_s("\n");
}
-3.000 5.000 1.000 9.000