Path: utzoo!utgpu!water!watmath!clyde!rutgers!husc6!bloom-beacon!gatech!hubcap!ncrcae!ncr-sd!hp-sdd!hplabs!decwrl!labrea!rocky!rokicki
From: rokicki@rocky.STANFORD.EDU (Tomas Rokicki)
Newsgroups: comp.sys.amiga
Subject: Structure alignment in Manx C
Keywords: Watch out!
Message-ID: <1042@rocky.STANFORD.EDU>
Date: 13 Feb 88 20:54:14 GMT
Organization: Stanford University Computer Science Department
Lines: 28

I just tracked down this bug that took me immense amounts of time
to find, and I discovered something about Manx C.  I found out that
one of my friends had also run into and wasted hours finding this
anomaly.  Specifically,  Manx C does not long-word align structures
containing long words!  (It also doesn't apparently long-word align
long words.)  The ramifications of this are two-fold:

- Programs compiled with Manx C and then run on a 68020 system will
run slower, as some (probably half) of their long word accesses will
need two memory accesses instead of one.

- You cannot statically allocate anything that needs to be on a long
word boundary; for instance, packets.  (Not that you should anyway, as
they should be MEMF_PUBLIC, but with the current release that doesn't
matter anyway.)  Anything that will be converted to a BPTR and back
will have problems.

Oh yeah, this is Manx 3.4b.

I can't think of any good way to fix this problem; I refuse to recompile
all my programs with 32-bit ints.  Why did Manx do this?  The only case
where it costs anything is in passing arguments to subroutines; all other
occurances would cost very little memory at all.  And subroutine arguments
could be handled as they are now, or perhaps modified.  I don't care.

What does Lattice do (4.0), anyone out there know?

-tom