gh-37201: Fix univariate polynomial reverse

    
For univariate polynomials over "non-prime" finite fields, the reverse
method had an issue when specifying `degree=0`: it raised an error
saying that this optional argument should be... nonnegative (which 0
is).

Example:
```
sage: ring.<x> = GF(9)[]
sage: pol = ring(1)
sage: pol.reverse(degree=2)
x^2
sage: pol.reverse()
1
sage: pol.reverse(degree=0)
------------------------------------------------------------------------
---
ValueError                                Traceback (most recent call
last)
Cell In[5], line 1
----> 1 pol.reverse(degree=Integer(0))

File ~/repositories/software/sage/src/sage/rings/polynomial/polynomial_z
z_pex.pyx:537, in
sage.rings.polynomial.polynomial_zz_pex.Polynomial_ZZ_pEX.reverse()
    535 if degree is not None:
    536     if degree <= 0:
--> 537         raise ValueError("degree argument must be a non-negative
integer, got %s" % (degree))
    538     try:
    539         d = degree

ValueError: degree argument must be a non-negative integer, got 0
```

This is fixed in this PR, along with fixes in similar code where the
error message was not the expected one ("cannot convert to long",
instead of "degree must be nonnegative").
    
URL: #37201
Reported by: Vincent Neiger
Reviewer(s): Xavier Caruso

src/sage/matrix/matrix_polynomial_dense.pyx

@@ -675,7 +675,7 @@ cdef class Matrix_polynomial_dense(Matrix_generic_dense):
             sage: M.reverse([2,3,-1])
             Traceback (most recent call last):
             ...
-            OverflowError: can't convert negative value to unsigned long
+            ValueError: degree argument must be a non-negative integer, got -1
 
         .. SEEALSO::
 

src/sage/rings/polynomial/polynomial_element.pyx

@@ -7672,9 +7672,11 @@ cdef class Polynomial(CommutativePolynomial):
 
         cdef unsigned long d
         if degree is not None:
+            if degree < 0:
+                raise ValueError("degree argument must be a non-negative integer, got %s" % (degree))
             d = degree
             if d != degree:
-                raise ValueError("degree argument must be a non-negative integer, got %s"%(degree))
+                raise ValueError("degree argument must be a non-negative integer, got %s" % (degree))
             if len(v) < degree+1:
                 v.reverse()
                 v = [self.base_ring().zero()]*(degree+1-len(v)) + v

src/sage/rings/polynomial/polynomial_integer_dense_flint.pyx

@@ -1827,9 +1827,11 @@ cdef class Polynomial_integer_dense_flint(Polynomial):
         cdef Polynomial_integer_dense_flint res = self._new()
         cdef unsigned long d
         if degree is not None:
+            if degree < 0:
+                raise ValueError("degree argument must be a non-negative integer, got %s" % (degree))
             d = degree
             if d != degree:
-                raise ValueError("degree argument must be a non-negative integer, got %s" % degree)
+                raise ValueError("degree argument must be a non-negative integer, got %s" % (degree))
             # FLINT expects length
             fmpz_poly_reverse(res._poly, self._poly, d+1)
         else:

src/sage/rings/polynomial/polynomial_zmod_flint.pyx

@@ -815,9 +815,11 @@ cdef class Polynomial_zmod_flint(Polynomial_template):
         cdef Polynomial_zmod_flint res = self._new()
         cdef unsigned long d
         if degree is not None:
+            if degree < 0:
+                raise ValueError("degree argument must be a non-negative integer, got %s" % (degree))
             d = degree
             if d != degree:
-                raise ValueError("degree argument must be a non-negative integer, got %s"%(degree))
+                raise ValueError("degree argument must be a non-negative integer, got %s" % (degree))
             nmod_poly_reverse(&res.x, &self.x, d+1) # FLINT expects length
         else:
             nmod_poly_reverse(&res.x, &self.x, nmod_poly_length(&self.x))

src/sage/rings/polynomial/polynomial_zz_pex.pyx

@@ -513,13 +513,18 @@ cdef class Polynomial_ZZ_pEX(Polynomial_template):
             sage: f.reverse(degree=200)
             2*x^200 + 3*x^199 + 5*x^198 + 7*x^197 + 11*x^196 + 13*x^195 + 17*x^194 + 19*x^193
             sage: f.reverse(degree=0)
-            Traceback (most recent call last):
-            ...
-            ValueError: degree argument must be a non-negative integer, got 0
+            2
             sage: f.reverse(degree=-5)
             Traceback (most recent call last):
             ...
             ValueError: degree argument must be a non-negative integer, got -5
+
+        Check that this implementation is compatible with the generic one::
+
+            sage: p = R([0,1,0,2])
+            sage: all(p.reverse(d) == Polynomial.reverse(p, d)
+            ....:     for d in [None, 0, 1, 2, 3, 4])
+            True
         """
         self._parent._modulus.restore()
 
@@ -533,11 +538,10 @@ cdef class Polynomial_ZZ_pEX(Polynomial_template):
         # When a degree has been supplied, ensure it is a valid input
         cdef unsigned long d
         if degree is not None:
-            if degree <= 0:
+            if degree < 0:
                 raise ValueError("degree argument must be a non-negative integer, got %s" % (degree))
-            try:
-                d = degree
-            except ValueError:
+            d = degree
+            if d != degree:
                 raise ValueError("degree argument must be a non-negative integer, got %s" % (degree))
             ZZ_pEX_reverse_hi(r.x, (<Polynomial_ZZ_pEX> self).x, d)
         else: