#18096: Libsingular conversion of (signed?) int to sage might have a
muisunderstanding about bitlength
--------------------------+----------------------------
Reporter: nbruin | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.6
Component: interfaces | Keywords:
Merged in: | Authors:
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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Note (in singular)
{{{
> LIB "normal.lib";
> ring r=0,(x,y,z),dp;
> ideal i=(x-y)*(y-z)*(z-x);
> genus(i);
-2
}}}
whereas in sage:
{{{
sage: x,y,z = QQ['x,y,z'].gens()
sage: C= Curve((x-y)*(y-z)*(z-x));
sage: sage: import sage.libs.singular.function_factory
sage: sage: sing_genus =
sage.libs.singular.function_factory.ff.normal__lib.genus
sage: I=C.defining_ideal()
sage: sing_genus(I)
4294967294
}}}
so somehow the -2 seems to be represented in libsingular as a 32-bit
signed integer and gets interpreted by sage as (probably) a 64-bit signed
integer. The relevant code lives in
sage.lib.singular.function.pyx:951 (to_python):
{{{
elif rtyp == INT_CMD:
return <long>to_convert.data
}}}
Oddly enough, most of libsingular seems to refer to such fields with a
`(long)` cast as well, and I would expect that, since sage and libsingular
are supposed to be compiled with compatible compilers, they would agree on
what `long` means.
--
Ticket URL: <http://trac.sagemath.org/ticket/18096>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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