create correct Singular coeffs with create_ring_from_singular_ring (#773

)

Co-authored-by: Max Horn <[email protected]>

deps/src/coeffs.cpp

@@ -236,6 +236,38 @@ void singular_define_coeffs(jlcxx::Module & Singular)
     return bool(nCoeff_is_algExt(n));
   });
 
+  Singular.method("nCoeff_is_Nemo_AnticNumberField", [](coeffs n) {
+    return n->type==n_Nemo_AnticNumberField;
+  });
+
+  Singular.method("nCoeff_is_Nemo_QQField", [](coeffs n) {
+    return n->type==n_Nemo_QQField;
+  });
+
+  Singular.method("nCoeff_is_Nemo_ZZRing", [](coeffs n) {
+    return n->type==n_Nemo_ZZRing;
+  });
+
+  Singular.method("nCoeff_is_Nemo_FqPolyRepField", [](coeffs n) {
+    return n->type==n_Nemo_FqPolyRepField;
+  });
+
+  Singular.method("nCoeff_is_Nemo_fqPolyRepField", [](coeffs n) {
+    return n->type==n_Nemo_fqPolyRepField;
+  });
+
+  Singular.method("nCoeff_is_Nemo_Field", [](coeffs n) {
+    return n->type==n_Nemo_Field;
+  });
+
+  Singular.method("nCoeff_is_Nemo_Ring", [](coeffs n) {
+    return n->type==n_Nemo_Ring;
+  });
+
+  Singular.method("nGetCoeffData", [](coeffs n) {
+    return n->data;
+  });
+
   /* make a copy of a coefficient domain (actually just increments a
    * reference count) */
   Singular.method("nCopyCoeff", &nCopyCoeff);

src/caller.jl

@@ -192,6 +192,12 @@ function create_ring_from_singular_ring(r::libSingular.ring_ptr)
       minpoly = F(libSingular.algExt_GetMinpoly(c, F.ptr))
       basering = N_AlgExtField(libSingular.nCopyCoeff(c), minpoly)
       T = n_algExt
+   elseif libSingular.nCoeff_is_Nemo_Field(c) || libSingular.nCoeff_is_Nemo_Ring(c)
+      cf = libSingular.nCopyCoeff(c)
+      data_ptr = libSingular.nGetCoeffData(cf)
+      R = unsafe_pointer_to_objref(data_ptr)
+      basering = CoefficientRing(R)  # FIXME: should we set cache=false ?
+      T = elem_type(basering)
    else
       basering = N_UnknownSingularCoefficientRing(libSingular.nCopyCoeff(c))
       T = n_unknownsingularcoefficient

test/caller-test.jl

@@ -249,3 +249,10 @@ end
     @test Singular.libSingular.random() == 16807
     @test Singular.libSingular.random() == 282475249
 end
+
+@testset "Nemo coeffs" begin
+    F = Nemo.fraction_field(Nemo.polynomial_ring(Nemo.ZZ)[1])
+    R, x = Singular.polynomial_ring(F, [:x])
+    S = Singular.create_ring_from_singular_ring(Singular.libSingular.rCopy(R.ptr))
+    @test base_ring(R) == base_ring(S)
+end