Fix overflow in historical scoring model point count summation #3616
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In adb0afc we started raising bucket weights to the power four in the historical model. This improved our model's accuracy greatly, but resulted in a much larger `total_valid_points_tracked`. In the same commit we converted `total_valid_points_tracked` to a float, but retained the 64-bit integer math to build it out of integer bucket values. Sadly, 64 bits are not enough to sum 1024 bucket pairs of 16-bit integers multiplied together and then squared (we need 16*4 + 10 = 74 bits to avoid overflow). Thus, here we replace the summation with 128-bit integers.
wpaulino
approved these changes
Feb 24, 2025
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Landing as trivial |
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Backported in #3616 |
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In adb0afc we started raising bucket weights to the power four in the historical model. This improved our model's accuracy greatly, but resulted in a much larger
total_valid_points_tracked. In the same commit we convertedtotal_valid_points_trackedto a float, but retained the 64-bit integer math to build it out of integer bucket values.Sadly, 64 bits are not enough to sum 1024 bucket pairs of 16-bit integers multiplied together and then squared (we need 16*4 + 10 = 74 bits to avoid overflow). Thus, here we replace the summation with 128-bit integers.