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include/tl/algorithm/bits.h

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+#pragma once
+
+#include "tl/detail/prologue.h"
+#include "tl/functional.h"
+
+namespace tl
+{
+namespace algorithm
+{
+
+//////////////////////////////////////////////////////////////////////////
+
+/**
+ * @brief Count the number of bit set for the given value.
+ */
+inline uint8_t bits_count(uint32_t i_value) noexcept
+{
+#if defined(_MSC_VER)
+	return uint8_t(__popcnt(i_value));
+#elif defined(__clang__) || defined(__GNUC__)
+	return uint8_t(__builtin_popcount(i_value));
+#else
+	static_assert(!std::is_same_v<T, T>, "no-builtin function found for this compiler");
+#endif
+}
+
+//////////////////////////////////////////////////////////////////////////
+
+/**
+ * @brief Count the number of bit set for the given value.
+ */
+inline uint64_t bits_count(uint64_t i_value) noexcept
+{
+#if defined(_MSC_VER)
+#if defined(TL_PLATFORM_64)
+	return uint8_t(__popcnt64(i_value));
+#elif defined(TL_PLATFORM_32)
+	return bits_count(uint32_t(i_value >> 32)) + bits_count(uint32_t(i_value & 0xffffffff));
+#else 
+	static_assert(!std::is_same_v<T, T>, "no-builtin function found for this compiler);");
+#endif // TL_PLATFORM_XX
+#elif defined(__clang__) || defined(__GNUC__)
+	return uint8_t(__builtin_popcountl(i_value));
+#else
+	static_assert(!std::is_same_v<T, T>, "no-builtin function found for this compiler");
+#endif
+}
+
+//////////////////////////////////////////////////////////////////////////
+
+/**
+ * @brief Position of the top bit set to 1.
+ * @param the given value
+ * @return  -1 in case value is 0 otherwise the position.
+ */
+inline int8_t top_bit(uint32_t i_value) noexcept
+{
+#if defined(_MSC_VER)
+	unsigned long index = 0;
+	return _BitScanReverse(&index, (unsigned long)i_value) ? uint8_t(index) : -1;
+#elif defined(__clang__) || defined(__GNUC__)
+	return i_value ? 31u - __builtin_clzl(i_value) : -1;
+#else
+	static_assert(!std::is_same_v<T, T>, "no-builtin function found for this compiler);");
+#endif
+}
+
+//////////////////////////////////////////////////////////////////////////
+
+/**
+ * @brief Position of the top bit set to 1.
+ * @param the given value
+ * @return  -1 in case value is 0 otherwise the position.
+ */
+inline int8_t top_bit(uint64_t i_value) noexcept
+{
+#if defined(_MSC_VER)
+	unsigned long index = 0;
+#if defined(TL_PLATFORM_64)
+	return _BitScanReverse64(&index, (unsigned long long)i_value) ? uint8_t(index) : -1;
+#elif defined(TL_PLATFORM_32)
+	const int8_t position = top_bit(uint32_t(i_value >> 32));
+	if (position > -1)
+	{
+		return position + 32;
+	}
+	
+	return top_bit(uint32_t(i_value & 0xffffffff));
+#else 
+	static_assert(!std::is_same_v<T, T>, "no-builtin function found for this compiler);");
+#endif // TL_PLATFORM_XX
+#elif defined(__clang__) || defined(__GNUC__)
+	return i_value ? 63u - __builtin_clzll(i_value) : -1;
+#else
+	static_assert(!std::is_same_v<T, T>, "no-builtin function found for this compiler);");
+#endif
+}
+
+//////////////////////////////////////////////////////////////////////////
+
+} // namespace algorithm
+} // namespace tl