utils: F-strings are missing the letter "f"

Also adds tests for utils ValueError strings.

(@whitequark) Adding tests/test_utils.py in the cherry-pick, slightly
modified from the one in `main` to remove tests for `TypeError` when
a float is passed.

Author: mcclure

amaranth/utils.py

@@ -9,7 +9,7 @@ def ceil_log2(n):
     Raises a `ValueError` for negative inputs."""
     n = operator.index(n)
     if n < 0:
-        raise ValueError("{n} is negative")
+        raise ValueError(f"{n} is negative")
     if n == 0:
         return 0
     return (n - 1).bit_length()
@@ -21,7 +21,7 @@ def exact_log2(n):
     Raises a `ValueError` if `n` is not a power of two."""
     n = operator.index(n)
     if n <= 0 or (n & (n - 1)):
-        raise ValueError("{n} is not a power of 2")
+        raise ValueError(f"{n} is not a power of 2")
     return (n - 1).bit_length()
 
 def log2_int(n, need_pow2=True):

tests/test_utils.py

@@ -0,0 +1,71 @@
+import unittest
+
+from amaranth.utils import *
+from amaranth._utils import _ignore_deprecated
+
+
+class Log2TestCase(unittest.TestCase):
+    def test_ceil_log2(self):
+        self.assertEqual(ceil_log2(0), 0)
+        self.assertEqual(ceil_log2(1), 0)
+        self.assertEqual(ceil_log2(2), 1)
+        self.assertEqual(ceil_log2(3), 2)
+        self.assertEqual(ceil_log2(4), 2)
+        self.assertEqual(ceil_log2(5), 3)
+        self.assertEqual(ceil_log2(8), 3)
+        self.assertEqual(ceil_log2(9), 4)
+        with self.assertRaises(TypeError):
+            ceil_log2(1.5)
+        with self.assertRaisesRegex(ValueError, r"^-1 is negative$"):
+            ceil_log2(-1)
+
+    def test_exact_log2(self):
+        self.assertEqual(exact_log2(1), 0)
+        self.assertEqual(exact_log2(2), 1)
+        self.assertEqual(exact_log2(4), 2)
+        self.assertEqual(exact_log2(8), 3)
+        for val in [-1, 0, 3, 5, 6, 7, 9]:
+            with self.assertRaisesRegex(ValueError, (f"^{val} is not a power of 2$")):
+                exact_log2(val)
+        with self.assertRaises(TypeError):
+            exact_log2(1.5)
+
+    @_ignore_deprecated
+    def test_log2_int(self):
+        self.assertEqual(log2_int(1), 0)
+        self.assertEqual(log2_int(2), 1)
+        self.assertEqual(log2_int(4), 2)
+        self.assertEqual(log2_int(8), 3)
+        for val in [-1, 3, 5, 6, 7, 9]:
+            with self.assertRaises(ValueError):
+                log2_int(val)
+        self.assertEqual(log2_int(0, False), 0)
+        self.assertEqual(log2_int(1, False), 0)
+        self.assertEqual(log2_int(2, False), 1)
+        self.assertEqual(log2_int(3, False), 2)
+        self.assertEqual(log2_int(4, False), 2)
+        self.assertEqual(log2_int(5, False), 3)
+        self.assertEqual(log2_int(8, False), 3)
+        self.assertEqual(log2_int(9, False), 4)
+
+    def test_bits_for(self):
+        self.assertEqual(bits_for(-4), 3)
+        self.assertEqual(bits_for(-3), 3)
+        self.assertEqual(bits_for(-2), 2)
+        self.assertEqual(bits_for(-1), 1)
+        self.assertEqual(bits_for(0), 1)
+        self.assertEqual(bits_for(1), 1)
+        self.assertEqual(bits_for(2), 2)
+        self.assertEqual(bits_for(3), 2)
+        self.assertEqual(bits_for(4), 3)
+        self.assertEqual(bits_for(5), 3)
+        self.assertEqual(bits_for(-4, True), 3)
+        self.assertEqual(bits_for(-3, True), 3)
+        self.assertEqual(bits_for(-2, True), 2)
+        self.assertEqual(bits_for(-1, True), 1)
+        self.assertEqual(bits_for(0, True), 1)
+        self.assertEqual(bits_for(1, True), 2)
+        self.assertEqual(bits_for(2, True), 3)
+        self.assertEqual(bits_for(3, True), 3)
+        self.assertEqual(bits_for(4, True), 4)
+        self.assertEqual(bits_for(5, True), 4)