Re: [boost] Boost SIMD beta release

Subject: Re: [boost] Boost SIMD beta release
From: Domagoj Saric (dsaritz_at_[hidden])
Date: 2012-12-24 11:16:13

"Peter Dimov"  wrote in message 
news:EC9066EE5B5448A2B4BAF64570BE6BAD_at_pdimov5...
> Yes, and the right thing to do is...

Actually there is a "significant"[1] portion of cases where alignment 
problems can be fixed more elegantly. If we realize that protected memory 
systems have page-size-granularity which is much larger than any conceivable 
SIMD vector size it immediately follows that "overread" (reading outside of 
the specified range) of a maximum size of "SIMD-cardinal - 1" is always 
safe. Further more in a single threaded case or when you allocate your 
arrays with both their location and size aligned, overwrite is also always 
safe when you wrap the overwrite in a guard class that automatically aligns 
the array pointers/iterators and then simply restores any possibly 
overwritten elements in its destructor (NT2/Boost.SIMD devs might recall the 
discussion of EdgeRestoredOutputRange on the mailing list and/or IRC). This 
only requires that all the arrays be compatibly aligned (i.e. if one is off 
by 1 and the other by 2 this approach cannot be used) but it covers almost 
all of my/our own cases (usually it only does not cover cases that arise 
when crossing 3rd party library/legacy interfaces)...

@NT2 devs, I might have missed it but I didn't see you mention your 
shifted-iterator functionality in this context...

[1] I know, a weasel word...to make it less so I'm referring to my 
experience with digital signal processing...

-- 
"What Huxley teaches is that in the age of advanced technology, spiritual
devastation is more likely to come from an enemy with a smiling face than
from one whose countenance exudes suspicion and hate."
Neil Postman