git patch-id is not bad for this: Here are the four commits with "Fix roundoff p...

git patch-id is not bad for this:

Here are the four commits with "Fix roundoff problems in float8_timestamptz() and make_interval()" as their commit message:

  $ git log --pretty="%h - %d" --date-order --all --grep=float8_time 
  1888fad440 -  (origin/REL9_4_STABLE)
  7786b98482 -  (origin/REL9_5_STABLE)
  404756fe89 -  (origin/REL9_6_STABLE)
  8f93bd8512 -

And here's what "git patch-id" thinks of them:

  $ git log -p --date-order --all --grep=float8_time | git patch-id
  cd559dd389e09655a64c3c6f41c2f76e6fd72b77 1888fad440036195c7e7a933fc17410fad8dcc3d
  cd559dd389e09655a64c3c6f41c2f76e6fd72b77 7786b984825ea720aed3a11ee465dc3d6cfc8d96
  63a51849977948d89992cbfbbd86c2598c92072f 404756fe89f62735f6075abb594b54be9c262b27
  63a51849977948d89992cbfbbd86c2598c92072f 8f93bd8512466c9b6c4dbc1e5efd0f72b8e2be9a

It can tell that the 9.4 and 9.5 patches are identical to each other, and that the 9.6 and master patches are also identical to each other. But there were differences between the two groups.