test: Use python3.8 pow()

test/functional/test_framework/util.py

@@ -542,18 +542,7 @@ def modinv(a, n):
     """Compute the modular inverse of a modulo n using the extended Euclidean
     Algorithm. See https://en.wikipedia.org/wiki/Extended_Euclidean_algorithm#Modular_integers.
     """
-    # TODO: Change to pow(a, -1, n) available in Python 3.8
-    t1, t2 = 0, 1
-    r1, r2 = n, a
-    while r2 != 0:
-        q = r1 // r2
-        t1, t2 = t2, t1 - q * t2
-        r1, r2 = r2, r1 - q * r2
-    if r1 > 1:
-        return None
-    if t1 < 0:
-        t1 += n
-    return t1
+    return pow(a, -1, n)
 
 class TestFrameworkUtil(unittest.TestCase):
     def test_modinv(self):