fix prime=0 selected for domain=1

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## Unreleased
 ### Fixed
 - Very large seeds no longer cause integer overflow
+- 0 is no longer selected as coprime for domain=1
 
 
 ## [0.0.2] - 2024-10-12

shufflish/__init__.py

@@ -79,6 +79,9 @@ def _modular_prime_combinations(domain, primes, k):
     Generate all ``k``-combinations of the given primes that are unique mod ``domain``.
     Only considers primes that are coprime with ``domain``.
     """
+    if domain == 1:
+        yield 1
+        return
     primes = list(dict.fromkeys(p % domain for p in primes if domain % p != 0))
     seen = set()
     ones = (1,) * (k-1)
@@ -96,6 +99,9 @@ def _modular_prime_combinations_with_repetition(domain, primes, k):
     Only considers primes that are coprime with ``domain``.
     May repeat values.
     """
+    if domain == 1:
+        yield 1
+        return
     ones = (1,) * (k-1)
     primes = list(dict.fromkeys(p % domain for p in primes if domain % p != 0))
     for p1, p2, p3 in combinations(chain(ones, primes), k):
@@ -196,6 +202,8 @@ def _select_prime(
     Only considers primes that are coprime with ``domain``.
     This can be quite slow.
     """
+    if domain == 1:
+        return 1
     gen = _modular_prime_combinations(domain, primes, k)
     num_comb = None
     if primes is PRIMES and domain in NUM_COMBINATIONS:
@@ -221,6 +229,8 @@ def _select_prime_with_repetition(
     Return the product of this combination mod domain.
     This is reasonably fast, but does not account for reptitions mod domain.
     """
+    if domain == 1:
+        return 1
     ones = (1,) * (k-1)
     primes = list(chain(ones, dict.fromkeys(p % domain for p in primes if domain % p != 0)))
     np = len(primes)
@@ -302,7 +312,6 @@ def permutation(
         raise ValueError("domain must be < 2**63")
     if seed is None:
         seed = random.randrange(2**64)
-    # Step 1: Select coprime number
     if allow_repetition:
         prime = _select_prime_with_repetition(domain, seed, primes, num_primes)
     else:

test/test_completeness.py

@@ -9,17 +9,18 @@ def _is_complete(p, domain):
     assert len(set(p)) == domain, (p, domain)
 
 
-def test_permutations_class():
+def test_permutations_function():
     for domain in (1, 2, 3, 5, 7, 10, 11, 13, 100):
         for seed in range(domain):
             _is_complete(permutation(domain, seed), domain)
 
 
-def test_permutation_function():
+def test_permutation_class():
     for domain in (1, 2, 3, 5, 7, 10, 11, 13, 100):
         perms = Permutations(domain)
+        print(perms.coprimes)
         assert len(perms.coprimes) > 0, domain
-        for seed in range(domain):
+        for seed in range(domain * len(perms.coprimes)):
             _is_complete(perms.get(seed), domain)