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 *    notice, this list of conditions and the following disclaimer in the
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 *    contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
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 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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 */

////////////////////////////////////////////////////////////////////////////////
// export C interface
extern "C" void computeGold(float *id, float *od, int w, int h, int r);

// CPU implementation
void hboxfilter_x(float *id, float *od, int w, int h, int r)
{
    float scale = 1.0f / (2 * r + 1);

    for (int y = 0; y < h; y++) {
        float t;
        // do left edge
        t = id[y * w] * r;

        for (int x = 0; x < r + 1; x++) {
            t += id[y * w + x];
        }

        od[y * w] = t * scale;

        for (int x = 1; x < r + 1; x++) {
            int c = y * w + x;
            t += id[c + r];
            t -= id[y * w];
            od[c] = t * scale;
        }

        // main loop
        for (int x = r + 1; x < w - r; x++) {
            int c = y * w + x;
            t += id[c + r];
            t -= id[c - r - 1];
            od[c] = t * scale;
        }

        // do right edge
        for (int x = w - r; x < w; x++) {
            int c = y * w + x;
            t += id[(y * w) + w - 1];
            t -= id[c - r - 1];
            od[c] = t * scale;
        }
    }
}

void hboxfilter_y(float *id, float *od, int w, int h, int r)
{
    float scale = 1.0f / (2 * r + 1);

    for (int x = 0; x < w; x++) {
        float t;
        // do left edge
        t = id[x] * r;

        for (int y = 0; y < r + 1; y++) {
            t += id[y * w + x];
        }

        od[x] = t * scale;

        for (int y = 1; y < r + 1; y++) {
            int c = y * w + x;
            t += id[c + r * w];
            t -= id[x];
            od[c] = t * scale;
        }

        // main loop
        for (int y = r + 1; y < h - r; y++) {
            int c = y * w + x;
            t += id[c + r * w];
            t -= id[c - (r * w) - w];
            od[c] = t * scale;
        }

        // do right edge
        for (int y = h - r; y < h; y++) {
            int c = y * w + x;
            t += id[(h - 1) * w + x];
            t -= id[c - (r * w) - w];
            od[c] = t * scale;
        }
    }
}

////////////////////////////////////////////////////////////////////////////////
//! Compute reference data set
//! @param image      pointer to input data
//! @param temp       pointer to temporary store
//! @param w          width of image
//! @param h          height of image
//! @param r          radius of filter
////////////////////////////////////////////////////////////////////////////////

void computeGold(float *image, float *temp, int w, int h, int r)
{
    hboxfilter_x(image, temp, w, h, r);
    hboxfilter_y(temp, image, w, h, r);
}
