Re: Git and GCC

[Nix <nix@esperi.org.uk>]

On 8 Dec 2007, Johannes Schindelin said:

> Hi,
>
> On Sat, 8 Dec 2007, J.C. Pizarro wrote:
>
>> On 2007/12/07, "Linus Torvalds" <torvalds@linux-foundation.org> wrote:
>>
>> > SHA1 is almost totally insignificant on x86. It hardly shows up. But 
>> > we have a good optimized version there.
>> 
>> If SHA1 is slow then why dont he contribute adding Haval160 (3 rounds) 
>> that it's faster than SHA1? And to optimize still more it with SIMD 
>> instructions in kernelspace and userland.
>
> He said SHA-1 is insignificant.

Actually davem also said it *is* significant on SPARC. But of course
J. C. Pizarro's suggested solution won't work because you can't just go
around replacing SHA-1 in git with something else :) you could *add* new
hashing methods, but you couldn't avoid SHA-1, and adding a new hashing
method would bloat every object and every hash in objects like commits
with an indication of which hashing method was in use.

(But you know this.)

>> 1.   "Don't compress this repo but compact this uncompressed repo
>>       using minimal spanning forest and deltas"

... and then you do a git-gc. Oops, now what?

... or perhaps you want to look something up in the pack. Now you have to
unpack a large hunk of the whole damn thing.

>> 2.   "After, compress this whole repo with LZMA (e.g. 48MiB) from 7zip before
>>       burning it to DVD for backup reasons or before replicating it to
>>	internet".
>
> Patches? ;-)

Replicating a pack to the internet is almost invariably replicating
*parts* of a pack anyway, which reduces to the problem with option 1
above...

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