[Vm-dev] Fwd: [squeak-dev] Questionable comment
cunningham.cb at gmail.com
Fri Aug 21 23:58:40 UTC 2015
sorry, wrong list. Will do it right in future. Mostly.
---------- Forwarded message ----------
From: Chris Cunningham <cunningham.cb at gmail.com>
Date: Fri, Aug 21, 2015 at 4:16 PM
Subject: Re: [squeak-dev] Questionable comment
To: The general-purpose Squeak developers list <
squeak-dev at lists.squeakfoundation.org>
On Thu, Aug 20, 2015 at 9:25 PM, Eliot Miranda <eliot.miranda at gmail.com>
> Hi Chris,
> On Wed, Aug 19, 2015 at 1:06 PM, Chris Cunningham <cunningham.cb at gmail.com
> > wrote:
>> well, not questionable - bad.
>> (in ByteArray)
>> long64At: index
>> "Answer a 64-bit integer in Smalltalk order (little-endian)."
>> | n1 n2 |
>> n1 := self unsignedLongAt: index bigEndian: true.
>> n2 := self unsignedLongAt: index+4 bigEndian: true.
>> These are obviously bigEndian now, nto litte-endian.
>> Does this mean Smalltalk order (or now Squeak order) has changed?
> This is not for general purpose. The method is part of VMMaker. Let's
> take it to vm-dev.
> It's a simple mistake. If you look at long64At:put: you'll see the
> comment is correct:
Yes. I had loaded the VMMaker to look at the ARM jit code (I'm working on
an ARM simulator - fun project), and then forgot I had it loaded. then
later, I needed to pull 64-bit integers out of a structure (while writing a
KAFKA interface) and stumbled on this. I think a generalized 64 bit
put/access would be useful, and maybe even a general 128 bit too (although
I have no need for it at this time).
> long64At: index put: val
> "I store 64-bit integers in Smalltalk (little-endian) order."
> self unsignedLongAt: index put: (val bitAnd: 16rFFFFFFFF) bigEndian: false.
> self unsignedLongAt: index+4 put: (val bitShift: -32) bigEndian: false.
> I'm now confused. Not only is the comment wrong, but it looks like the
code is wrong. The get (#long64At:) is actually getting the 64-bit integer
in big-endian order (as witnessed by the two sub-calls, too), while the put
it truly doing it in little-endian format.
Or am I missing something?
> Thanks for finding this!
> best, Eliot
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