Create find_previous_power_of_two.py

bit_manipulation/find_previous_power_of_two.py

@@ -0,0 +1,45 @@
+# https://stackoverflow.com/questions/1322510/given-an-integer-how-do-i-find-the-next-largest-power-of-two-using-bit-twiddlin
+
+def find_previous_power_of_two(n: int) -> int:
+    """
+    Find the largest power of two that is less than or equal to a given integer.
+
+    >>> find_previous_power_of_two(10)
+    8
+    >>> find_previous_power_of_two(16)
+    16
+    >>> find_previous_power_of_two(5)
+    4
+    >>> find_previous_power_of_two(1)
+    1
+    >>> find_previous_power_of_two(0)
+    0
+    >>> find_previous_power_of_two(-5)
+    Traceback (most recent call last):
+        ...
+    ValueError: Input must be a non-negative integer
+    >>> find_previous_power_of_two(10.5)
+    Traceback (most recent call last):
+        ...
+    TypeError: Input must be an integer
+    """
+
+    if not isinstance(n, int):
+        raise TypeError("Input must be an integer")
+
+    if n < 0:
+        raise ValueError("Input must be a non-negative integer")
+
+    if n == 0:
+        return 0
+
+    power = 1
+    while power <= n:
+        power <<= 1  # Equivalent to multiplying by 2
+
+    return power >> 1
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()