On Tuesday 23 November 2010, VictorMiller wrote:
> Thanks! Then perhaps Sage should raise an exception when it gets back
> genus -1 from singular.
Here's what Hannes Schönemann from the Singular team replied to me when I
reported this on [libsingular-devel]:
"""
Singular uses (currently) 32bit int on all platforms.
Here our overflow detection represents -1 as a result of a subtraction
as 4294967295.
Fix (in Singular/iparith.cc, routine jjMINUS_I):
--- iparith.cc (Revision 13661)
+++ iparith.cc (Arbeitskopie)
@@ -697,14 +697,18 @@
}
static BOOLEAN jjMINUS_I(leftv res, leftv u, leftv v)
{
- unsigned int a=(unsigned int)(unsigned long)u->Data();
- unsigned int b=(unsigned int)(unsigned long)v->Data();
+ void *ap=u->Data(); void *bp=v->Data();
+ int aa=(int)(long)ap;
+ int bb=(int)(long)bp;
+ int cc=aa-bb;
+ unsigned int a=(unsigned int)(unsigned long)ap;
+ unsigned int b=(unsigned int)(unsigned long)bp;
unsigned int c=a-b;
if (((Sy_bit(31)&a)!=(Sy_bit(31)&b))&&((Sy_bit(31)&a)!=(Sy_bit(31)&c)))
{
WarnS("int overflow(-), result may be wrong");
}
- res->data = (char *)((long)c);
+ res->data = (char *)((long)cc);
return jjPLUSMINUS_Gen(res,u,v);
}
"""
It seems with the new patch the overflow would at least be detected? Can you
give it a try?
Cheers,
Martin
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