tree aaa386e3d32769a0ee1d3661118a2fe32c842e18
parent 0cce44c63391aedd4436ec0c940f8b84d6b1301f
author Ruiling Song <ruiling.song@intel.com> 1565851596 +0800
committer Cheng Chen <chengchen@google.com> 1565974066 +0000

Avoid underflow in exp()

Too small negative values will cause underflow in exp().
Here we only care the value that can be accumulated.
So the clamp has no effect on final result.
exp(-15)*1000*255 = 0.07
exp(-20)*1000*65535 = 0.13

BUG=aomedia:2433

Change-Id: I00d171822cbcc45c30e5c38987c900fb5cfba7d8