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digitalmars.D - unsigned < 0

reply bearophile <bearophileHUGS lycos.com> writes:
Recently I have shown some bugs (and added few enhancement requests):
http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=129069

Among those there is my suggestion to statically disallow unsigned<0
comparisons:
http://d.puremagic.com/issues/show_bug.cgi?id=5539
So that's a little change in the D2 language itself, it's not a warning as the
one GCC shows on C code.

Recently Iain Buclaw has shown some patches for DMD:
http://d.puremagic.com/issues/show_bug.cgi?id=5490

Three cases were of unsigned < 0, like:

+++ b/src/optimize.c
   -351,7 +351,7    Expression *AddrExp::optimize(int result)
             {
                 TypeSArray *ts = (TypeSArray *)ve->type;
                 dinteger_t dim = ts->dim->toInteger();
-                if (index < 0 || index >= dim)
+                if (index >= dim)
                     error("array index %jd is out of bounds [0..%jd]", index,
dim);
                 e = new SymOffExp(loc, ve->var, index * ts->nextOf()->size());
                 e->type = type;


Do you like this little change in the D2 language?

Bye,
bearophile
Feb 10 2011
parent reply bearophile <bearophileHUGS lycos.com> writes:
 Do you like this little change in the D2 language?

To avoid troubles in generic code you need a little workaround: if (__traits(isUnsigned, x) || x >= 0) { ... Bye, bearophile
Feb 10 2011
parent reply bearophile <bearophileHUGS lycos.com> writes:
 To avoid troubles in generic code you need a little workaround:
 if (__traits(isUnsigned, x) || x >= 0) { ...

That's not good enough yet. The first part of the test needs to be done in a static if. Bye, bearophile
Feb 10 2011
parent reply Iain Buclaw <ibuclaw ubuntu.com> writes:
== Quote from bearophile (bearophileHUGS lycos.com)'s article
 To avoid troubles in generic code you need a little workaround:
 if (__traits(isUnsigned, x) || x >= 0) { ...


 Bye,
 bearophile

You also need to watch out for code like this too: if (T.min < 0) { ... As that could possibly trigger off unsigned < 0 warnings too. Regards Iain
Feb 11 2011
parent bearophile <bearophileHUGS lycos.com> writes:
Iain Buclaw:

 You also need to watch out for code like this too:
 if (T.min < 0) { ...
 As that could possibly trigger off unsigned < 0 warnings too.

I was not talking about warnings. I was talking about changing the D language, turning that into a _error_ if x is unsigned. Bye, bearophile
Feb 11 2011