Derrick Stolee 02d577fd7b test-tool: add helper for name-hash values
Add a new test-tool helper, name-hash, to output the value of the
name-hash algorithms for the input list of strings, one per line.

Since the name-hash values can be stored in the .bitmap files, it is
important that these hash functions do not change across Git versions.
Add a simple test to t5310-pack-bitmaps.sh to provide some testing of
the current values. Due to how these functions are implemented, it would
be difficult to change them without disturbing these values.

Create a performance test that uses test_size to demonstrate how
collisions occur for these hash algorithms. This test helps inform
someone as to the behavior of the name-hash algorithms for their repo
based on the paths at HEAD.

My copy of the Git repository shows modest statistics around the
collisions of the default name-hash algorithm:

Test                                              this tree
-----------------------------------------------------------------
5314.1: paths at head                                        4.5K
5314.2: number of distinct name-hashes                       4.1K
5314.3: number of distinct full-name-hashes                  4.5K
5314.4: maximum multiplicity of name-hashes                    13
5314.5: maximum multiplicity of fullname-hashes                 1

Here, the maximum collision multiplicity is 13, but around 10% of paths
have a collision with another path.

In a more interesting example, the microsoft/fluentui [1] repo had these
statistics at time of committing:

Test                                              this tree
-----------------------------------------------------------------
5314.1: paths at head                                       19.6K
5314.2: number of distinct name-hashes                       8.2K
5314.3: number of distinct full-name-hashes                 19.6K
5314.4: maximum multiplicity of name-hashes                   279
5314.5: maximum multiplicity of fullname-hashes                 1

[1] https://github.com/microsoft/fluentui

That demonstrates that of the nearly twenty thousand path names, they
are assigned around eight thousand distinct values. 279 paths are
assigned to a single value, leading the packing algorithm to sort
objects from those paths together, by size.

In this repository, no collisions occur for the full-name-hash
algorithm.

In a more extreme example, an internal monorepo had a much worse
collision rate:

Test                                              this tree
-----------------------------------------------------------------
5314.1: paths at head                                      221.6K
5314.2: number of distinct name-hashes                      72.0K
5314.3: number of distinct full-name-hashes                221.6K
5314.4: maximum multiplicity of name-hashes                 14.4K
5314.5: maximum multiplicity of fullname-hashes                 2

Even in this repository with many more paths at HEAD, the collision rate
was low and the maximum number of paths being grouped into a single
bucket by the full-path-name algorithm was two.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
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Git for Windows

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This is Git for Windows, the Windows port of Git.

The Git for Windows project is run using a governance model. If you encounter problems, you can report them as GitHub issues, discuss them on Git for Windows' Google Group, and contribute bug fixes.

To build Git for Windows, please either install Git for Windows' SDK, start its git-bash.exe, cd to your Git worktree and run make, or open the Git worktree as a folder in Visual Studio.

To verify that your build works, use one of the following methods:

  • If you want to test the built executables within Git for Windows' SDK, prepend <worktree>/bin-wrappers to the PATH.

  • Alternatively, run make install in the Git worktree.

  • If you need to test this in a full installer, run sdk build git-and-installer.

  • You can also "install" Git into an existing portable Git via make install DESTDIR=<dir> where <dir> refers to the top-level directory of the portable Git. In this instance, you will want to prepend that portable Git's /cmd directory to the PATH, or test by running that portable Git's git-bash.exe or git-cmd.exe.

  • If you built using a recent Visual Studio, you can use the menu item Build>Install git (you will want to click on Project>CMake Settings for Git first, then click on Edit JSON and then point installRoot to the mingw64 directory of an already-unpacked portable Git).

    As in the previous bullet point, you will then prepend /cmd to the PATH or run using the portable Git's git-bash.exe or git-cmd.exe.

  • If you want to run the built executables in-place, but in a CMD instead of inside a Bash, you can run a snippet like this in the git-bash.exe window where Git was built (ensure that the EOF line has no leading spaces), and then paste into the CMD window what was put in the clipboard:

    clip.exe <<EOF
    set GIT_EXEC_PATH=$(cygpath -aw .)
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    set GIT_TEMPLATE_DIR=$(cygpath -aw templates/blt)
    set GITPERLLIB=$(cygpath -aw perl/build/lib)
    EOF
    
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    C:\git-sdk-64\usr\src\git\git.exe --exec-path=C:\git-sdk-64\usr\src\git help
    

    Note: for this to work, you have to hard-link (or copy) the .dll files from the /mingw64/bin directory to the Git worktree, or add the /mingw64/bin directory to the PATH somehow or other.

To make sure that you are testing the correct binary, call ./git.exe version in the Git worktree, and then call git version in a directory/window where you want to test Git, and verify that they refer to the same version (you may even want to pass the command-line option --build-options to look at the exact commit from which the Git version was built).

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See Documentation/gittutorial.txt to get started, then see Documentation/giteveryday.txt for a useful minimum set of commands, and Documentation/git-<commandname>.txt for documentation of each command. If git has been correctly installed, then the tutorial can also be read with man gittutorial or git help tutorial, and the documentation of each command with man git-<commandname> or git help <commandname>.

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Description
A fork of Git containing Windows-specific patches.
Readme 515 MiB
2025-08-19 03:50:05 -05:00
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