How to use keypoints from another library to OpenCV?

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I'm using the Fast SIFT Image Features Library, which is incredibly faster than the OpenCV implementation (approx 0.01 sec for keypoints and descriptors computations!).

This is the code about how keypoints+descriptor are created:

...
Image image = ReadPGM(stdin);
Keypoint keypts;
keypts = GetKeypoints(image);

Where:

typedef struct KeypointSt {
    float row, col;             // Subpixel location of keypoint.
    float scale, ori;           // Scale and orientation (range [-PI,PI])
    float descrip[128];     // Vector of descriptor values
    struct KeypointSt *next;    // Pointer to next keypoint in list.
} *Keypoint;

ReadPGM definition isn't relevant for this question.

So my question is: how can I use keypts obtained from the code above in OpenCV?