Add base::count_bits() function

base/count_bits.h

@@ -0,0 +1,28 @@
+// LAF Base Library
+// Copyright (c) 2023 Igara Studio S.A.
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#ifndef BASE_COUNT_BITS_H_INCLUDED
+#define BASE_COUNT_BITS_H_INCLUDED
+#pragma once
+
+#include <cstddef>
+#include <limits>
+
+namespace base {
+
+  template<typename T>
+  constexpr inline size_t count_bits(const T v) {
+    size_t n = 0;
+    for (size_t b=0; b<sizeof(T)*8; ++b) {
+      if (v & (T(1) << b))
+        ++n;
+    }
+    return n;
+  }
+
+}
+
+#endif

base/count_bits_tests.cpp

@@ -0,0 +1,45 @@
+// LAF Base Library
+// Copyright (c) 2023  Igara Studio S.A.
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#include <gtest/gtest.h>
+
+#include "base/ints.h"
+#include "base/count_bits.h"
+
+using namespace base;
+
+TEST(CountBits, CommonCases)
+{
+  EXPECT_EQ(0, count_bits(0));
+  EXPECT_EQ(1, count_bits(1));
+  EXPECT_EQ(1, count_bits(2));
+  EXPECT_EQ(2, count_bits(3));
+}
+
+TEST(CountBits, Limits)
+{
+  EXPECT_EQ(32, count_bits(0xffffffff));
+  EXPECT_EQ(64, count_bits(0xffffffffffffffffll));
+}
+
+TEST(CountBits, UnsignedLong)
+{
+  EXPECT_EQ(1, count_bits<unsigned long>(1));
+  EXPECT_EQ(10, count_bits<unsigned long>(1023));
+}
+
+TEST(CountBits, Rgb30bpp)
+{
+  EXPECT_EQ(10, count_bits<unsigned long>(0x3ff));
+  EXPECT_EQ(10, count_bits<unsigned long>(0xffc00));
+  EXPECT_EQ(10, count_bits<unsigned long>(0x3ff00000));
+}
+
+int main(int argc, char** argv)
+{
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}