_mm_msub_ss

Artigo
07/22/2011

[Note: This document describes a pre-release version of Visual Studio 2010 SP1 and may be revised in any later version.]

Visual Studio 2010 SP1 is required.

Microsoft Specific

Generates the FMA4 XMM instruction vfmsubss to perform a single-round floating-point multiply-subtract of the low-order floating-point values of its sources.

__m128 _mm_msub_ss (
   __m128 src1,
   __m128 src2,
   __m128 src3
);

Parameters

[in] src1
A 128-bit parameter that contains a 32-bit floating-point value in the low doubleword.
[in] src2
A 128-bit parameter that contains a 32-bit floating-point value in the low doubleword.
[in] src3
A 128-bit parameter that contains a 32-bit floating-point value in the low doubleword.

Return value

A 128-bit result r that contains four 32-bit floating-point values.

r[0] := src1[0] * src2[0] - src3[0];
r[1] := r[2] = r[3] = 0.;

Requirements

Intrinsic	Architecture
_mm_msub_ss	FMA4

Header file <intrin.h>

Remarks

The low-order single-precision floating-point value in src1 is multiplied by the corresponding value in src2, the corresponding value in src3 is subtracted from the product, and the result is stored as the corresponding value in the destination. The other values in src1, src2, and src3 are ignored, and the three high-order floating-point values of the result are set to 0.

The multiply- subtract is performed with a single round at the end, as if intermediate results were computed to infinite precision.

The vfmsubss 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_msub_ss(a, b, c);
    for (i = 0; i < 4; i++) printf_s(" %.3f", d.m128_f32[i]);
    printf_s("\n");
}

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Change History

Date	History	Reason
March 2011	Added this content.	SP1 feature change.

March 2011

Added this content.

SP1 feature change.

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