<div dir="ltr"><br><div class="gmail_extra"><br><br><div class="gmail_quote">2014-07-02 0:28 GMT+02:00 David T. Lewis <span dir="ltr"><<a href="mailto:lewis@mail.msen.com" target="_blank">lewis@mail.msen.com</a>></span>:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class=""><div class="h5"><br>
On Tue, Jul 01, 2014 at 09:21:00PM +0200, Nicolas Cellier wrote:<br>
><br>
> 2014-07-01 4:22 GMT+02:00 <<a href="mailto:commits@source.squeak.org">commits@source.squeak.org</a>>:<br>
><br>
> ><br>
> > Item was changed:<br>
> > ----- Method: LargeIntegersPlugin>>cDigitSub:len:with:len:into: (in<br>
> > category 'C core') -----<br>
> > + cDigitSub: pByteSmall len: smallLen with: pByteLarge len: largeLen into:<br>
> > pByteRes<br>
> > + | z |<br>
> > - cDigitSub: pByteSmall<br>
> > - len: smallLen<br>
> > - with: pByteLarge<br>
> > - len: largeLen<br>
> > - into: pByteRes<br>
> > - | z limit |<br>
> > <var: #pByteSmall type: 'unsigned char * '><br>
> > <var: #pByteLarge type: 'unsigned char * '><br>
> > <var: #pByteRes type: 'unsigned char * '><br>
> ><br>
> > + z := 0. "Loop invariant is -1<=z<=1"<br>
> > + 0 to: smallLen - 1 do:<br>
> > - z := 0.<br>
> > - "Loop invariant is -1<=z<=1"<br>
> > - limit := smallLen - 1.<br>
> > - 0 to: limit do:<br>
> > [:i |<br>
> > z := z + (pByteLarge at: i) - (pByteSmall at: i).<br>
> > + pByteRes at: i put: z - (z // 256 * 256). "sign-tolerant<br>
> > form of (z bitAnd: 255)"<br>
> ><br>
><br>
> Frankly, having z declared unsigned int and just doing pByteRes at: i put:<br>
> (z bitAnd: 16rFF) as I suggested would be way way simpler and will ALWAYS<br>
> work.<br>
> Why the hell invoke the complications of signed arithmetic when the content<br>
> pByteRes is unsigned???<br>
<br>
</div></div>Nicolas,<br>
<br>
This sounds right to me.<br>
<br>
Do you have a final version of #cDigitSub:len:with:len:into: that you can<br>
recommend? The version in VMMaker-nice.342 produces failures in the<br>
KernelTests-Numbers tests when compiled in 64-bit mode, but I think that<br>
you have since suggested some other improvements in this email thread.<br>
<br>
Dave<br>
<br>
</blockquote></div><br></div><div class="gmail_extra">Hi David,<br></div><div class="gmail_extra">that's interesting. VMMaker-nice.342 contains all the 32bits LargeInteger modifications, not just the #cDigitSub:len:with:len:into:.<br>
</div><div class="gmail_extra">I tried to declare everything as <unsigned int> rather than <usqInt> with the assumption that sizeof(unsigned int)*2==sizeof(unsigned long long).<br></div><div class="gmail_extra">
But I never tried to compile a 64 bits VM, I think I lost the recipe for brewing such a flavour.<br></div><div class="gmail_extra">I'm on MacOSX, could you provide a link to the shortest way to do it?<br></div><div class="gmail_extra">
Once I can check it, I'll publish a corrected version.<br></div><div class="gmail_extra">Thanks<br><br></div><div class="gmail_extra">Nicolas<br></div></div>