The usage of Apple GCC compiler option  -fast in the Mac VM 3.7.x VM  
has pointed out a compiler optimization issue that uncovers a bug in  
JPEGReadWriter2Plugin, Masahiro Sakai <masa at micronet-japan.jp> was kind  
enough to send me email about the issue.

JPEGReaderWriter2Plugin has

JPEGReaderWriter2Plugin>>initialiseModule
	self export: true



which translates to

EXPORT(int) initialiseModule(void) {
}

You will note the absence of a return value, this routine *is expected*  
to return true or false, the compiler when testing returns a value  
which is > 0 and we are happy, although I'm not sure why it does that  
or even if it does, perhaps it decided the routine doesn't exist?  
Certainly it gives a warning about a missing return value which we  
ignore, isn't C fun... Hah, a typed language...

However when the optimizer is turned on, then at a certain feature  
level it notices no return value and ensures the value is 0, versus say  
a random non-zero. Well it doesn't matter if you expect a value back,  
and don't give a value, then who knows???

Certainly compiler issues are fun to debug and this as a side effect  
causes the initialization of the JPEGReaderWriter2Plugin plugin to  
fail, and we fall back to the old Smalltalk code for JPEGS which does  
not understand progressive jpegs. Of course I'm quite curious about  
what compilers do  on other platforms with this code gem.

PS attached is a change set to add return true to the initialize and  
release module methods in JPEGReaderWriter2Plugin
--
======================================================================== 
===
John M. McIntosh <johnmci at smalltalkconsulting.com> 1-800-477-2659
Corporate Smalltalk Consulting Ltd.  http://www.smalltalkconsulting.com
======================================================================== 
===
-------------- next part --------------
A non-text attachment was scrubbed...
Name: JPEGReaderWriter2ProperInit.1.cs.gz
Type: application/x-gzip
Size: 421 bytes
Desc: not available
Url : http://lists.squeakfoundation.org/pipermail/squeak-dev/attachments/20031225/a13ed5fb/JPEGReaderWriter2ProperInit.1.cs.bin