Add set bits count using lookup table method

Introduced get_set_bits_count_using_lookup_table to efficiently count set bits in a 32-bit integer using a precomputed lookup table. Updated benchmark to compare the new method alongside existing algorithms.

Author: ArunKishoreVoleti

bit_manipulation/count_number_of_one_bits.py

@@ -60,27 +60,72 @@ def get_set_bits_count_using_modulo_operator(number: int) -> int:
     return result
 
 
+def get_set_bits_count_using_lookup_table(number: int) -> int:
+    """
+    Count the number of set bits in a 32-bit integer using a precomputed lookup table.
+    >>> get_set_bits_count_using_lookup_table(25)
+    3
+    >>> get_set_bits_count_using_lookup_table(37)
+    3
+    >>> get_set_bits_count_using_lookup_table(21)
+    3
+    >>> get_set_bits_count_using_lookup_table(58)
+    4
+    >>> get_set_bits_count_using_lookup_table(0)
+    0
+    >>> get_set_bits_count_using_lookup_table(256)
+    1
+    >>> get_set_bits_count_using_lookup_table(-1)
+    Traceback (most recent call last):
+        ...
+    ValueError: the value of input must not be negative
+    """
+    _LOOKUP_TABLE = [bin(i).count("1") for i in range(256)]
+
+    if number < 0:
+        raise ValueError("the value of input must not be negative")
+
+    # Split 32-bit number into four 8-bit chunks and use lookup table
+    return (
+        _LOOKUP_TABLE[number & 0xFF]
+        + _LOOKUP_TABLE[(number >> 8) & 0xFF]
+        + _LOOKUP_TABLE[(number >> 16) & 0xFF]
+        + _LOOKUP_TABLE[(number >> 24) & 0xFF]
+    )
+
+
+
 def benchmark() -> None:
     """
-    Benchmark code for comparing 2 functions, with different length int values.
-    Brian Kernighan's algorithm is consistently faster than using modulo_operator.
+    Benchmark code for comparing 3 functions, with different length int values.
+    Brian Kernighan's algorithm is consistently faster than using modulo_operator,
+    and the lookup table method is often the fastest for repeated calls.
     """
 
     def do_benchmark(number: int) -> None:
         setup = "import __main__ as z"
         print(f"Benchmark when {number = }:")
+
         print(f"{get_set_bits_count_using_modulo_operator(number) = }")
         timing = timeit(
             f"z.get_set_bits_count_using_modulo_operator({number})", setup=setup
         )
         print(f"timeit() runs in {timing} seconds")
+
         print(f"{get_set_bits_count_using_brian_kernighans_algorithm(number) = }")
         timing = timeit(
             f"z.get_set_bits_count_using_brian_kernighans_algorithm({number})",
             setup=setup,
         )
         print(f"timeit() runs in {timing} seconds")
 
+        print(f"{get_set_bits_count_using_lookup_table(number) = }")
+        timing = timeit(
+            f"z.get_set_bits_count_using_lookup_table({number})",
+            setup=setup,
+        )
+        print(f"timeit() runs in {timing} seconds")
+
     for number in (25, 37, 58, 0):
         do_benchmark(number)
         print()