Arun reported this from https://github.com/apache/storm/pull/1866#discussion_r95326528
Quoting his comment:
This should match the task selected by fields grouping https://github.com/apache/storm/blob/master/storm-core/src/jvm/org/apache/storm/daemon/GrouperFactory.java#L159.
The modulo technique will return a different value than Math.abs. Probably we should move it to some common utility function and use it in both places.
In 1.x branch the fields grouper doesn't seem to account for negative hashCode, so not sure why didn't it come up before. https://github.com/apache/storm/blob/1.x-branch/storm-core/src/clj/org/apache/storm/daemon/executor.clj#L52
So we should fix Nimbus code to use Math.abs on master, 1.x, 1.0.x branches, and also fix executor.clj to use Math.abs on 1.x, 1.0.x branches.