Commit Graph

51 Commits

Author SHA1 Message Date
James Zern
984734436d Fix variance (signed integer) overflow
In the variance calculations the difference is summed and later squared.
When the sum exceeds sqrt(2^31) the value is treated as a negative when
it is shifted which gives incorrect results.

To fix this we force the multiplication to be unsigned.

The alternative fix is to shift sum down by 4 before multiplying.
However that will reduce precision.

For 16x16 blocks the maximum sum is 65280 and sqrt(2^31) is 46340 (and
change).

This change is based on:
1698234 Missed some variance casts
fea3556 Fix variance overflow

Change-Id: I2c61856cca9db54b9b81de83b4505ea81a050a0f
2012-11-06 23:06:44 -08:00