Use of Offsets and Methods on a SDLT Primitive Example

Intel® oneAPI DPC++/C++ Compiler Developer Guide and Reference

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ID 767253

Date 11/07/2023

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Use of Offsets and Methods on a SDLT Primitive Example

This example demonstrates a linearized 2d stencil using embedded offsets and calling methods on the primitive.

#include <sdlt/sdlt.h>

// Typical C++ object to represent a pixel in an image
struct RGBs
{
    float red;
    float green;
    float blue;

    RGBs() {}
    RGBs(const RGBs &iOther)
        : red(iOther.red)
        , green(iOther.green)
        , blue(iOther.blue)
    {
    }

    RGBs & operator =(const RGBs &iOther)
    {
        red = iOther.red;
        green = iOther.green;
        blue = iOther.blue;
        return *this;
    }

    RGBs operator + (const RGBs &iOther) const
    {
        RGBs sum;
        sum.red = red + iOther.red;
        sum.green = green + iOther.green;
        sum.blue = blue + iOther.blue;
        return sum;
    }

    RGBs operator * (float iScalar) const
    {
        RGBs scaledColor;
        scaledColor.red = red * iScalar;
        scaledColor.green = green * iScalar;
        scaledColor.blue = blue * iScalar;
        return scaledColor;
    }
};

SDLT_PRIMITIVE(RGBs, red, green, blue)

const int StencilHaloSize = 1;
const int width = 1920;
const int height = 1080;

template<typename AccessorT> void loadImageStub(AccessorT) {}
template<typename AccessorT> void saveImageStub(AccessorT) {}


// performs average color filtering with neighbors left,right,above,below
void main(void)
{
    // We are padding +-1 so we can avoid boundary conditions
    const int paddedWidth = width + 2 * StencilHaloSize;
    const int paddedHeight = height + 2 * StencilHaloSize;
    int elementCount = paddedWidth*paddedHeight;
    sdlt::soa1d_container<RGBs> inputImage(elementCount);
    sdlt::soa1d_container<RGBs> outputImage(elementCount);

    loadImageStub(inputImage.access());

    SDLT_INLINE_BLOCK
    {
        const int endOfY = StencilHaloSize + height;
        const int endOfX = StencilHaloSize + width;
        for (int y = StencilHaloSize; y < endOfY; ++y)
        {
            // Embed offsets into Accessors to get the to correct row
            auto prevRow = inputImage.const_access((y - 1)*paddedWidth);
            auto curRow = inputImage.const_access(y*paddedWidth);
            auto nextRow = inputImage.const_access((y + 1)*paddedWidth);

            auto outputRow = outputImage.access(y*paddedWidth);

            #pragma omp simd
            for (int ix = StencilHaloSize; ix < endOfX; ++ix)
            {
                sdlt::linear_index x(ix);

                const RGBs color1 = curRow[x - 1];
                const RGBs color2 = curRow[x];
                const RGBs color3 = curRow[x + 1];
                const RGBs color4 = prevRow[x];
                const RGBs color5 = nextRow[x];
                // Despite looking like AOS code, compiler is able to create
                // privatized instances and call inlinable methods on the objects
                // keeping the algorithm at very high level
                const RGBs sumOfColors = color1 + color2 + color3 + color4 + color5;
                const RGBs averageColor = sumOfColors*(1.0f / 5.0f);
                outputRow[x] = averageColor;
            }
        }
    }
    saveImageStub(outputImage.access());
}

Parent topic: Examples

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Intel® oneAPI DPC++/C++ Compiler Developer Guide and Reference

Use of Offsets and Methods on a SDLT Primitive Example