[Openmcl-devel] Windows versions of CCL available for smoke-testing
gb at clozure.com
Thu Oct 9 19:55:35 UTC 2008
On Thu, 9 Oct 2008, Brian Mastenbrook wrote:
> On Oct 9, 2008, at 12:59 PM, Gary Byers wrote:
>> On Thu, 9 Oct 2008, Brian Mastenbrook wrote:
>>> Very cool. Is this fully relocatable? This is probably less of an issue on
>>> Win64, of course.
>> We don't do relocation correctly on ia32 yet
>> (This would affect 32-bit Darwin and Linux as well as 32-bit Windows.)
> Interesting. Does this include things like NIL & friends?
>> AFAIK (and as far as I remember), it's worked correctly. The fact that
>> 'long' is only 32 bits on win64 has sometimes meant that "correctly" and
>> "as expected" aren't quite the same thing.
> This is what uint64_t and intptr_t are for, right? Most problematic uses of
> "long" that I've run into should in fact be intptr_t.
Yes, that it what things like that are for.
Given something like:
typedef uint64_t natural;
natural bits_in_last_word, nbits_in_word;
natural mask = ~((1L<<(nbits_in_word-bits_in_last_word))-1L);
I found it surprising that both the shift and subtraction were done in
32-bit aritmetic and the result was then sign-extended (IIRC, it was
sign-, not 0-extended) to 64 bits. (Conditionally) changing the 1L's
to 1LL's avoided the unexpected truncation of intermediate arithmetic
If I was more of a C weenie than I am, I probably shouldn't have been
surprised by that. Inscrutable C arithmetic rules and the fact that
1L is a 64-bit constant on other 64-bit platforms but a 32-bit constant
on win64 made the fact that 'mask' only ever had <= 32 significant bits
set hard to spot. I'm perfectly willing to believe that gcc's behavior
here was correct, but I doubt if I'm the only person who would find it
useless and unintuitive. (I'd also be willing to believe that it's
a bug, but I find it very difficult to distinguish between C compiler
bugs and "correct but useless C compiler behavior".)
As practical advice, I think that it's fair to say that the fact that
'long' is 32 bits wide on win64 will likely introduce surprising
> Brian Mastenbrook
> brian at mastenbrook.net
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