fastScoreHarris vs fastDetect threshold

[protobits]

Hi,
I don't really understand the example given on the README:

pislam::fastDetect<640, 16>(width, height, &img[y], &out[y], 20);
pislam::fastScoreHarris<640, 16>(width, height, &img[y], 1 << 15, &out[y]);

You pass 20 as a threshold for the first function and then 1 << 15 for the second. What is the relation between these two and how do I interpret the second threshold?

Thanks