Fixes error in calculating multiplication order #532

src/galois/_fields/_array.py

@@ -1044,7 +1044,7 @@ def multiplicative_order(self) -> int | np.ndarray:
             k = np.log(x)  # x as an exponent of α
             order = (field.order - 1) // np.gcd(field.order - 1, k)
         else:
-            d = np.array(divisors(field.order - 1))  # Divisors d such that d | p^m - 1
+            d = np.array(divisors(field.order - 1), dtype=field.dtypes[-1])  # Divisors d such that d | p^m - 1
             y = np.power.outer(x, d)  # x^d -- the first divisor d for which x^d == 1 is the order of x
             idxs = np.argmin(y, axis=-1)  # First index of divisors, which is the order of x
             order = d[idxs]  # The order of each element of x

tests/fields/test_arithmetic_methods.py

@@ -6,6 +6,8 @@
 import numpy as np
 import pytest
 
+import galois
+
 
 def test_additive_order(field_additive_order):
     GF, X, Z = field_additive_order["GF"], field_additive_order["X"], field_additive_order["Z"]
@@ -34,6 +36,14 @@ def test_multiplicative_order(field_multiplicative_order):
         GF.Range(0, 2).multiplicative_order()
 
 
+def test_issue_532():
+    """
+    https://github.com/mhostetter/galois/issues/532
+    """
+    GF = galois.GF(2**64 - 59)
+    assert GF(1).multiplicative_order() == 1
+
+
 def test_characteristic_poly_element(field_characteristic_poly_element):
     GF, X, Z = (
         field_characteristic_poly_element["GF"],