[Toybox] Going through Oliver's xz commit list...

[enh]

between https://android-review.googlesource.com/c/platform/external/xz-embedded/+/3032623
and https://android-review.googlesource.com/c/platform/external/xz-embedded/+/3040077
i ended up disabling this stuff on android. the bug link you can't
follow on the first change has one of the OTA guys experimenting and
finding that (a) there's no size decrease for an OTA package and (b)
there's a 2% time cost. another OTA guy questioned whether the
experiment had been done right, but given our assumption that this
optimization is effectively done already for dynamic binaries
(courtesy of the PLT) it didn't seem worth putting in further effort
to try to prove any value to this, and all things being equal, less
code is better.

note that if you go in the other direction and do want this stuff,
there's also a new risc-v implementation too.

On Tue, Jun 24, 2025 at 6:59 PM Oliver Webb <aquahobbyist at proton.me> wrote:
>
> On Tuesday, June 24th, 2025 at 17:37, Rob Landley <rob at landley.net> wrote:
> > On Feb 23, 2024, Oliver Webb triaged the xz-embedded commit list since
> > our version forked off from the upstream public domain one, and highlighted:
> >
> > > commit 89094f05f02b Adds the ARM64 BCJ encoder
> > > commit 8f3ed8b1759a Adds a MicroLZMA decoder
> > > commit 6f0e0c41e368 Add xz_dec_catrun() to support concatenated files
> >
> >
> > I applied the first one (but don't have a test file for it, maybe
> > compressing an arm64 binary with debian's xz would exercise that
> > codepath), and am applying the third now,
>
> Assuming you've already applied the 3rd one, did you experience any breaks in testing?
> There doesn't seem to be any decompression errors, and test_xzcat passes, but I remember trying
> to add these upstream commits some time ago and running into errors:
>
> "I tried on 6f0ec4 (Add xz_dec_catrun), got it to compile, but not to
> pass the test suite or decode linux-kernel tarballs.|
>
> -   Oliver Webb <aquahobbyist at proton.me>
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