Make your git commits lucky!
With this simple tool, you can change the start of your git commit hashes to whatever you want.
$ git log
1f6383a Some commit
$ lucky_commit
$ git log
0000000 Some commit
As a demonstration, see the latest commit in this repository.
lucky-commit
amends your commit messages by adding a few characters of various types of whitespace, and keeps trying new messages until it finds a good hash. By default, it will keep searching until it finds a hash starting with "0000000", but this can be changed by simply passing the desired hash as an argument.
$ lucky_commit 1010101
$ git log
1010101 Some commit
¯\_(ツ)_/¯
- Make sure you have
rustc
andcargo
installed. Installation instructions can be found here. - Run
cargo install lucky_commit --locked
Depending on your cargo
setup, this will usually add the binary to your $PATH
. You can then use it by running lucky_commit
.
Alternatively, you can build from source:
$ git clone https://github.com/not-an-aardvark/lucky-commit
$ cd lucky-commit/
$ cargo build --release
This will create the lucky_commit
binary (lucky_commit.exe
on Windows) in the target/release
directory. You can move this to wherever you want, or set up an alias for it.
By default, lucky-commit
links with your system's OpenCL headers and runs on a GPU. This makes it significantly faster.
However, if you encounter a linker error along the lines of /usr/bin/ld: cannot find -lOpenCL
, there are a few workarounds:
-
Compile
lucky-commit
without OpenCL by adding the flag--no-default-features
to your install or build command (i.e.cargo install lucky_commit --locked --no-default-features
orcargo build --release --no-default-features
). This will makelucky-commit
fall back to a multithreaded CPU implementation. The CPU implementation is about 10x slower on my laptop, but depending on what you're planning to use the tool for, there's a good chance it's fast enough anyway.This is the recommended approach if you just want a stable build, and you don't need the extra performance from GPUs.
-
You can try installing the OpenCL libraries for your system. The instructions for this will vary by OS (see e.g. here). Note that this will only be useful if your machine has a GPU.
-
You can try installing an older version of the library written in a different language (see the branches for Node.js, C, and pure Rust without OpenCL). Note that these older versions are drastically slower than the current version, and are also unmaintained.
lucky-commit
can be installed from the community repository using pacman:
$ pacman -S lucky-commit
lucky-commit
can be installed from dev-kit:
$ emerge dev-util/lucky-commit
lucky-commit
's performance is determined by how powerful your computer is, whether you GPG-sign your commits, and whether you use experimental git features.
The main bottleneck is SHA1 throughput. The default hash prefix of 0000000
has length 7, so on average, lucky-commit
needs to compute 167 SHA1 hashes.
For non-GPG-signed commits, lucky-commit
adds its whitespace to a 64-byte-aligned block at the very end of the commit message. Since everything that precedes the whitespace is constant for any particular commit, this allows lucky-commit
to cache the SHA1 buffer state and only hash a single 64-byte block on each attempt.
Hash searching is extremely parallelizable, and lucky-commit
takes advantage of this by running on a GPU when available. (The intuitive idea is that if you pretend that your commits are actually graphical image data, where SHA1 is a "shading" that gets applied to the whole image at once, and the resulting commit shorthashes are, say, RGBA pixel color values, then you can hash a large number of commits at once by just "rendering the image".)
The GPU on my 2015 MacBook Pro can compute about 196 million single-block hashes per second. As a result, the theoretical average time to find a 0000000
commit hash on my laptop is (167 hashes) / (196000000 hashes/s) = 1.37 seconds. You can estimate the average time for your computer by running time lucky_commit --benchmark
.
Outside of hashing, the tool also has to do a constant amount of I/O (e.g. spawning git
a few times), resulting in an observed average time on my laptop of about 1.6 seconds.
For GPG-signed commits, the commit message is part of the signed payload, so lucky-commit
can't edit the commit message without making the signature invalid. Instead, it adds its whitespace to the end of the signature itself. Since the signature precedes the commit message in git's commit encoding, this requires lucky-commit
to do more work on each attempt (it can't cache the SHA1 buffer state as effectively, and it needs to rehash the commit message every time). As a result, the performance for GPG-signed commits depends on the length of the commit message. This multiplies the average search time by roughly 1 + ceiling(commit message length / 64 bytes)
.
Finally, lucky-commit
also supports git repositories using the experimental sha256 object format. If lucky-commit
detects that it's being run in a repository with sha256 objects, it will automatically customize the sha256 shorthash of the commit at HEAD
, rather than the sha1 shorthash. The hash rate for sha256 is a bit slower than the hash rate for sha1.
If you're wondering whether your repository uses sha256, then it probably doesn't. At the time of writing, this is a highly experimental feature and is very rarely used.