fmpz_poly / fmpz now uses exact division

Previously an error would be raised instead.

Author: oscarbenjamin

src/flint/test/test.py

@@ -2319,6 +2319,33 @@ def test_division_scalar():
         assert raises(lambda: "AAA" / R(5), TypeError)
 
 
+def test_division_poly():
+    Z = flint.fmpz
+    Q = flint.fmpq
+    F17 = lambda x: flint.nmod(x, 17)
+    ctx = flint.fmpz_mod_ctx(163)
+    F163 = lambda a: flint.fmpz_mod(a, ctx)
+    PZ = lambda x: flint.fmpz_poly(x)
+    PQ = lambda x: flint.fmpq_poly(x)
+    PF17 = lambda x: flint.nmod_poly(x, 17)
+    PF163 = lambda x: flint.fmpz_mod_poly(x, flint.fmpz_mod_poly_ctx(163))
+    # fmpz exact scalar division
+    assert PZ([2, 4]) / Z(2) == PZ([1, 2])
+    assert PZ([2, 4]) / 2 == PZ([1, 2])
+    assert raises(lambda: PZ([2, 5]) / Z(2), DomainError)
+    assert raises(lambda: PZ([2, 5]) / 2, DomainError)
+    # field division by scalar
+    for (K, PK) in [(Q, PQ), (F17, PF17), (F163, PF163)]:
+        assert PK([2, 5]) / K(2) == PK([K(2)/K(2), K(5)/K(2)])
+        assert PK([2, 5]) / 2 == PK([K(2)/K(2), K(5)/K(2)])
+    # No other scalar division is allowed
+    for (R, PR) in [(Z, PZ), (Q, PQ), (F17, PF17), (F163, PF163)]:
+        assert raises(lambda: R(2) / PR([2, 5]), TypeError)
+        assert raises(lambda: 2 / PR([2, 5]), TypeError)
+        assert raises(lambda: PR([2, 5]) / 0, ZeroDivisionError)
+        assert raises(lambda: PR([2, 5]) / R(0), ZeroDivisionError)
+
+
 def test_division_matrix():
     Z = flint.fmpz
     Q = flint.fmpq
@@ -2517,12 +2544,14 @@ def setbad(obj, i, val):
         assert raises(lambda: P([1, 2, 1]) % P([0]), ZeroDivisionError)
         assert raises(lambda: divmod(P([1, 2, 1]), P([0])), ZeroDivisionError)
 
+        # Exact/field scalar division
         if is_field:
             assert P([2, 2]) / 2 == P([1, 1])
             assert P([1, 2]) / 2 == P([S(1)/2, 1])
-            assert raises(lambda: P([1, 2]) / 0, ZeroDivisionError)
         else:
-            assert raises(lambda: P([2, 2]) / 2, TypeError)
+            assert P([2, 2]) / 2 == P([1, 1])
+            assert raises(lambda: P([1, 2]) / 2, DomainError)
+        assert raises(lambda: P([1, 2]) / 0, ZeroDivisionError)
 
         assert raises(lambda: 1 / P([1, 1]), TypeError)
         assert raises(lambda: P([1, 2, 1]) / P([1, 1]), TypeError)
@@ -3105,6 +3134,7 @@ def test_all_tests():
     test_fmpz_mod_mat,
 
     test_division_scalar,
+    test_division_poly,
     test_division_matrix,
 
     test_polys,

src/flint/types/fmpz_poly.pyx

@@ -19,7 +19,7 @@ from flint.types.arb cimport arb
 from flint.types.acb cimport any_as_acb_or_notimplemented
 cimport libc.stdlib
 from flint.flintlib.fmpz cimport fmpz_init, fmpz_clear, fmpz_set
-from flint.flintlib.fmpz cimport fmpz_is_one, fmpz_equal_si, fmpz_equal
+from flint.flintlib.fmpz cimport fmpz_is_zero, fmpz_is_one, fmpz_equal_si, fmpz_equal
 from flint.flintlib.acb_modular cimport *
 from flint.flintlib.ulong_extras cimport n_is_prime
 from flint.flintlib.fmpz_poly cimport *
@@ -29,6 +29,9 @@ from flint.flintlib.acb cimport *
 from flint.flintlib.arb_poly cimport *
 from flint.flintlib.arb_fmpz_poly cimport *
 
+from flint.utils.flint_exceptions import DomainError
+
+
 cdef any_as_fmpz_poly(x):
     cdef fmpz_poly res
     if typecheck(x, fmpz_poly):
@@ -227,6 +230,20 @@ cdef class fmpz_poly(flint_poly):
     def __rmul__(self, other):
         return self._mul_(other)
 
+    def __truediv__(fmpz_poly self, other):
+        cdef fmpz_poly res
+        other = any_as_fmpz(other)
+        if other is NotImplemented:
+            return other
+        if fmpz_is_zero((<fmpz>other).val):
+            raise ZeroDivisionError("fmpz_poly division by 0")
+        res = fmpz_poly.__new__(fmpz_poly)
+        fmpz_poly_scalar_divexact_fmpz(res.val, self.val, (<fmpz>other).val)
+        # Check division is exact - there should be a better way to do this
+        if res * other != self:
+            raise DomainError("fmpz_poly division is not exact")
+        return res
+
     def _floordiv_(self, other):
         cdef fmpz_poly res
         if fmpz_poly_is_zero((<fmpz_poly>other).val):