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Date: Sun, 09 Feb 2014 06:35:27 +0000
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Subject: 64 bit runs slower than 32 bit?
From: lester@lsces.co.uk (Lester Caine)

When using Google one rarely gets the right answer until you already know the 
right questions to ask ...

That 64bit runs slower than 32bit has always niggled me since when moving up 
from 8/16 bit platforms to 32 bits one always saw a substantial speed improvement.

I've been asking the wrong questions about 'timing attach' used to decode 
passwords simply because I've been looking at the wrong questions, and the 
detailed analysis being supplied was convincing. But it's based on a lower level 
mistake. The 'timing attach' only works if one is doing 'byte by byte' compares 
and I'd not twigged that this was the mistake being made.

We tend to ignore just how something is achieved, so using memcmp() seems a 
sensible low level function, but it has a time penalty when all one wants is 
'='. It was not until I started to look at how it works that I found all the 
explanations on how having found a missmatch it then works out which character 
and produces the problem and the '<>' results. All the effort to produce a 
'safe' comparison on other c software aims to hide that timing difference? But 
why are we wasting time doing all that work? What is needed initially is to 
simply drop memcmp() and switch to a memequ() macro which bales as soon as a 
missmatch is found. It could have a flag which scans the whole buffer before 
baling if you want that extra 'safety'.

How often in the PHP code is memcmp() used when a simple memequ() would be 
faster ... and faster still on 64bit machines?

There is a side question here as to why with all the instructions available on 
processors there is not a 'byte compare' which produces the right set of flags 
in a single process cycle, but I suspect that fails as soon as you introduce 
unicode characters? memcmp() fails to produce the correct answer once one 
switches to a unicode base, while a memequ() would not have that problem?

-- 
Lester Caine - G8HFL
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