<br><br><div class="gmail_quote">On Wed, Sep 8, 2010 at 1:48 PM, John M McIntosh <span dir="ltr"><<a href="mailto:johnmci@smalltalkconsulting.com">johnmci@smalltalkconsulting.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<br>Let me try that with the correct email address...<br>
<br>
Begin forwarded message:<br>
<br>
> From: John M McIntosh <<a href="mailto:johnmci@smalltalkconsulting.com">johnmci@smalltalkconsulting.com</a>><br>
> Date: September 8, 2010 2:20:29 AM PDT<br>
> To: Squeak VM Developers <<a href="mailto:squeak-vmdev@lists.sourceforge.net">squeak-vmdev@lists.sourceforge.net</a>><br>
> Subject: squeak 32bit clean, no? yes?<br>
> Reply-To: <a href="mailto:johnmci@smalltalkconsulting.com">johnmci@smalltalkconsulting.com</a><br>
><br>
> It's 2:05am I should be in bed but I'm confused.<br>
><br>
> given BaseHeaderSize is 4<br>
> foo->newMethod is a usqInt (unsigned)<br>
><br>
> I see in a interp.c<br>
> Automatically generated from Squeak on #(27 April 2009 5:35:31 pm)<br>
><br>
> sqInt activateNewMethod(void) {<br>
> register struct foo * foo = &fum;<br>
> sqInt initialIP;<br>
> sqInt newContext;<br>
> sqInt where;<br>
> sqInt methodHeader;<br>
> sqInt tempCount;<br>
> sqInt i;<br>
> sqInt nilOop;<br>
> sqInt tmp;<br>
><br>
> methodHeader = longAt((foo->newMethod + BaseHeaderSize) + (HeaderIndex << ShiftForWord));<br>
><br>
><br>
> So that is a longAt: ( unsigned sqInt + 4)<br>
><br>
> But in the interp.c code I generated in July I have<br>
> methodPointer (a sqInt) = foo->newMethod (a usqint)<br>
> then<br>
> methodHeader = longAt((methodPointer + (BASE_HEADER_SIZE)) + (HeaderIndex << (SHIFT_FOR_WORD)));<br>
><br>
> So that is a longAt: (sqInt + 4).<br>
><br>
> Er so if foo->newMethod is > 0x7FFFFFFF won't that +4 not do what we think it should do?<br>
> Or should I go to bed now?<br></blockquote><div><br></div><div>Go to bed. In C (and in modulo arithmetic in general) (unsigned)((signed)v + N) == (unsigned)v + N. e.g. 0x80000000 + 4 is indeed (2^32 - 4) negated but that's also 0x80000004. i.e. the largest unsigned value is (unsigned)-1, all ones, and so when adding a positive value to a negative signed quantity you end up with a larger unsigned quantity.</div>
<div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
><br>
><br>
> /* Automatically generated from Squeak on 8 July 2010 12:32:36 pm<br>
> by VMMaker 4.2.6<br>
> */<br>
><br>
><br>
> sqInt activateNewMethod(void) {<br>
> register struct foo * foo = &fum;<br>
> sqInt tempCount;<br>
> sqInt nilOop;<br>
> sqInt where;<br>
> sqInt initialIP;<br>
> sqInt i;<br>
> sqInt newContext;<br>
> sqInt methodHeader;<br>
> sqInt methodPointer;<br>
> sqInt tmp;<br>
> sqInt activeCntx;<br>
> sqInt valuePointer;<br>
> sqInt valuePointer1;<br>
><br>
> /* begin headerOf: */<br>
> methodPointer = foo->newMethod;<br>
> methodHeader = longAt((methodPointer + (BASE_HEADER_SIZE)) + (HeaderIndex << (SHIFT_FOR_WORD)));<br>
><br>
><br>
> --<br>
> ===========================================================================<br>
> John M. McIntosh <<a href="mailto:johnmci@smalltalkconsulting.com">johnmci@smalltalkconsulting.com</a>> Twitter: squeaker68882<br>
> Corporate Smalltalk Consulting Ltd. <a href="http://www.smalltalkconsulting.com" target="_blank">http://www.smalltalkconsulting.com</a><br>
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--<br>
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John M. McIntosh <<a href="mailto:johnmci@smalltalkconsulting.com">johnmci@smalltalkconsulting.com</a>> Twitter: squeaker68882<br>
Corporate Smalltalk Consulting Ltd. <a href="http://www.smalltalkconsulting.com" target="_blank">http://www.smalltalkconsulting.com</a><br>
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