Re: [PATCH] Add a birdview-on-the-source-code section to the user manual

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: May 9, 2007, 22:23 UTC
Message-ID: <Pine.LNX.4.64.0705100015120.4167@racer.site>
In-Reply-To: <Pine.LNX.4.64.0705091625200.18541@iabervon.org>

Hi,

On Wed, 9 May 2007, Daniel Barkalow wrote:

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> On Wed, 9 May 2007, Johannes Schindelin wrote:
> 
> > If you tell Git that it should look for commit e83c6516..., it will 
> > store the sha1 as 0xe8 0x3c 0x65 0x16 ... in memory, no matter which 
> > endianness the processor has.
> 
> But it would be really weird to get 0x90 0xf2 0x4a 0x60 ... 0x16 0x65 
> 0x3c 0xe8 unless you've got a 160-bit little-endian processor. That 
> would be as strange as having "Test" stored as 0x74 0x73 0x65 0x54, I 
> think.

I was not aware originally, that no arithmetic is involved in SHA-1 computation.

If you store large integers, it makes tons of sense to follow the endianness, especially if you do _both_ boolean and integer operations on them.

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> > Which was positively confusing for me, since I automatically searched 
> > for the sequence 0x90 0xf2 0x4a 0x60 ... (which is the tail of that 
> > hash).
> > 
> > But if all this sounds too confusing, I agree to delete the 
> > "(big-endian)".
> 
> If it confused you, there should be something there. Maybe "(in order)" 
> or something else implying that the underlying type is an octet 
> sequence, rather than a 160-bit integer?

Well, I am convinced by now that nobody could be as stupid as me, so I think it is good without such a hint :-)

Ciao, Dscho