Re: [PATCH 0/4] Add a compile-time option to use the new, very fast sha1dc Rust crate

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi,

On Mon, 28 Sep 2026, Johannes Schindelin via GitGitGadget wrote:

> I stumbled across this new Rust crate last week. Its performance numbers are
> quite impressive. Naturally, I want to make use of this and get for Windows,

                                                          ^^^^^^^^^^^^^^^^^^^
							  in Git for Windows

My sincerest apologies; I am using Cohere Transcribe to compensate for my
inadequate typing speed, which typically works very, very well for me, yet
missed this typo. Likewise:

> which is used on many monorepos where this makes a real difference: In a
> pretty fast and loose test, I verified that a git index-pack runs roughly
> three times faster solely due to using those SIMD-based optimizations!
> 
> As a safety precaution, because this sha1dc crate is quite new, I wanted to
> introduce an escape hatch: core.sha1dcBackend=c, but turn it on by default,
> which is the reason for the three additional patches. Should these patches
> be undesirable for the Git project? I would not be mad at all if they were

                                    ^
				    , and

Sorry about that,
Johannes

> simply dropped.
> 
> Johannes Schindelin (4):
>   libgitcore: add `sha1dc` as an optional feature
>   sha1dc: allow selecting the C backend without rebuilding
>   pthread: provide `pthread_once()` shims for Windows and for
>     NO_PTHREADS
>   sha1dc: make `sha1dc_init()` thread-safe
> 
>  Cargo.toml                     |   4 ++
>  Documentation/config/core.adoc |   5 ++
>  Makefile                       |  29 +++++++++
>  compat/win32/pthread.c         |  16 +++++
>  compat/win32/pthread.h         |   5 ++
>  hash.h                         |   5 ++
>  sha1dc_git.c                   | 109 +++++++++++++++++++++++++++++++--
>  sha1dc_git.h                   |   5 +-
>  sha1dc_rs.h                    |  37 +++++++++++
>  src/lib.rs                     |   2 +
>  src/sha1dc_rs.rs               |  78 +++++++++++++++++++++++
>  t/helper/test-sha1.c           |  19 +++++-
>  t/t0013-sha1dc.sh              |  21 ++++++-
>  thread-utils.h                 |  16 +++++
>  14 files changed, 343 insertions(+), 8 deletions(-)
>  create mode 100644 sha1dc_rs.h
>  create mode 100644 src/sha1dc_rs.rs
> 
> 
> base-commit: 3bc0341126508f78f5869cbfc0005e987efdf0c7
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-2240%2Fdscho%2Foptionally-use-sha1dc-rs-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2240/dscho/optionally-use-sha1dc-rs-v1
> Pull-Request: https://github.com/gitgitgadget/git/pull/2240
> -- 
> gitgitgadget
>