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Date: Sat, 21 Apr 2012 01:26:21 +0200
From: magnum <john.magnum@...hmail.com>
To: john-dev@...ts.openwall.com
Subject: Re: cl_khr_byte_addressable_store
On 04/21/2012 01:03 AM, Solar Designer wrote:
> On Sat, Apr 21, 2012 at 12:45:56AM +0200, magnum wrote:
>> Then I'm afraid you lost me. Just how should I approach this? Should I
>> do two separate kernels or should I try some kind of bit-flipping
>> madness that just might work on both AMD and nvidia?
>
> I can't speak for Milen, but I guess that to write a byte you need to
> read a naturally aligned 4-byte word, mask out the original byte in it,
> OR in your new byte value, and write that word back. Of course, this is
> non-atomic, but you should not be accessing nearby bytes from another
> thread anyway.
>
> An obvious optimization would be to combine multiple byte writes
> together such that you read/write fewer words (such as one per 4 bytes).
Yes, thanks. I already do things similar to what you say for performance
reasons but the non-aligned cases will get nasty (or tedious at the very
least) if I am not allowed to ever write an unaligned byte. I am really
surprised by this limitation, this was not the obstacles I was picturing
when I got into this game.
The older I get, the older I become :)
magnum
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