git patch-id [--stable | --unstable]
Use a "stable" sum of hashes as the patch ID. With this option:--unstable
•Reordering file diffs that make up a patch does not affect the ID. In particular, two patches produced by comparing the same two trees with two different settings for "-O<orderfile>" result in the same patch ID signature, thereby allowing the computed result to be used as a key to index some meta-information about the change between the two trees;
•Result is different from the value produced by git 1.9 and older or produced when an "unstable" hash (see --unstable below) is configured - even when used on a diff output taken without any use of "-O<orderfile>", thereby making existing databases storing such "unstable" or historical patch-ids unusable.
This is the default if patchid.stable is set to true.
Use an "unstable" hash as the patch ID. With this option, the result produced is compatible with the patch-id value produced by git 1.9 and older. Users with pre-existing databases storing patch-ids produced by git 1.9 and older (who do not deal with reordered patches) may want to use this option.
This is the default.