| From: | Jeremy Kerr <jk(at)ozlabs(dot)org> |
|---|---|
| To: | Greg Stark <gsstark(at)mit(dot)edu> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, "<pgsql-hackers(at)postgresql(dot)org>" <pgsql-hackers(at)postgresql(dot)org>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>, Gurjeet Singh <singh(dot)gurjeet(at)gmail(dot)com> |
| Subject: | Re: [PATCH] backend: compare word-at-a-time in bcTruelen |
| Date: | 2009-06-16 13:23:41 |
| Message-ID: | 200906162123.42513.jk@ozlabs.org |
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| Thread: | |
| Lists: | pgsql-hackers |
Hi all,
> That's correct. To check the alignment you would have to look at the
> actual pointer. I would suggest using the existing macros to handle
> alignment. Hm, though the only one I see offhand which is relevant is
> the moderately silly PointerIsAligned(). Still it would make the code
> clearer even if it's pretty simple.
Yes, the code (incorrectly) assumes that any multiple-of-4 index into
the char array is aligned, and so the array itself must be aligned for
this to work.
I'll rework the patch, testing the pointer alignment directly instead.
> Incidentally, the char foo[4] = {' ',' ',' ',' '} suggestion is, I
> think, bogus. There would be no alignment guarantee on that array.
> Personally I'm find with 0x20202020 with a comment explaining what it
> is.
The variable is called 'spaces', but I can add extra comments if
preferred.
Cheers,
Jeremy
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