1 files changed, 155 insertions, 0 deletions
diff --git a/common/albit.h b/common/albit.h
new file mode 100644
index 00000000..ad596208
--- /dev/null
+++ b/common/albit.h
@@ -0,0 +1,155 @@
+#ifndef AL_BIT_H
+#define AL_BIT_H
+
+#include <cstdint>
+#include <limits>
+#include <type_traits>
+#if !defined(__GNUC__) && (defined(_WIN32) || defined(_WIN64))
+#include <intrin.h>
+#endif
+
+namespace al {
+
+#ifdef __BYTE_ORDER__
+enum class endian {
+    little = __ORDER_LITTLE_ENDIAN__,
+    big = __ORDER_BIG_ENDIAN__,
+    native = __BYTE_ORDER__
+};
+
+#else
+
+/* This doesn't support mixed-endian. */
+namespace detail_ {
+constexpr bool IsLittleEndian() noexcept
+{
+    static_assert(sizeof(char) < sizeof(int), "char is too big");
+
+    constexpr int test_val{1};
+    return static_cast<const char&>(test_val) ? true : false;
+}
+} // namespace detail_
+
+enum class endian {
+    big = 0,
+    little = 1,
+    native = detail_::IsLittleEndian() ? little : big
+};
+#endif
+
+
+/* Define popcount (population count/count 1 bits) and countr_zero (count
+ * trailing zero bits, starting from the lsb) methods, for various integer
+ * types.
+ */
+#ifdef __GNUC__
+
+namespace detail_ {
+    inline int popcount(unsigned long long val) noexcept { return __builtin_popcountll(val); }
+    inline int popcount(unsigned long val) noexcept { return __builtin_popcountl(val); }
+    inline int popcount(unsigned int val) noexcept { return __builtin_popcount(val); }
+
+    inline int countr_zero(unsigned long long val) noexcept { return __builtin_ctzll(val); }
+    inline int countr_zero(unsigned long val) noexcept { return __builtin_ctzl(val); }
+    inline int countr_zero(unsigned int val) noexcept { return __builtin_ctz(val); }
+} // namespace detail_
+
+template<typename T>
+inline std::enable_if_t<std::is_integral<T>::value && std::is_unsigned<T>::value,
+int> popcount(T v) noexcept { return detail_::popcount(v); }
+
+template<typename T>
+inline std::enable_if_t<std::is_integral<T>::value && std::is_unsigned<T>::value,
+int> countr_zero(T val) noexcept
+{ return val ? detail_::countr_zero(val) : std::numeric_limits<T>::digits; }
+
+#else
+
+/* There be black magics here. The popcount method is derived from
+ * https://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
+ * while the ctz-utilizing-popcount algorithm is shown here
+ * http://www.hackersdelight.org/hdcodetxt/ntz.c.txt
+ * as the ntz2 variant. These likely aren't the most efficient methods, but
+ * they're good enough if the GCC built-ins aren't available.
+ */
+namespace detail_ {
+    template<typename T, size_t = std::numeric_limits<T>::digits>
+    struct fast_utype { };
+    template<typename T>
+    struct fast_utype<T,8> { using type = std::uint_fast8_t; };
+    template<typename T>
+    struct fast_utype<T,16> { using type = std::uint_fast16_t; };
+    template<typename T>
+    struct fast_utype<T,32> { using type = std::uint_fast32_t; };
+    template<typename T>
+    struct fast_utype<T,64> { using type = std::uint_fast64_t; };
+
+    template<typename T>
+    constexpr T repbits(unsigned char bits) noexcept
+    {
+        T ret{bits};
+        for(size_t i{1};i < sizeof(T);++i)
+            ret = (ret<<8) | bits;
+        return ret;
+    }
+} // namespace detail_
+
+template<typename T>
+constexpr std::enable_if_t<std::is_integral<T>::value && std::is_unsigned<T>::value,
+int> popcount(T val) noexcept
+{
+    using fast_type = typename detail_::fast_utype<T>::type;
+    constexpr fast_type b01010101{detail_::repbits<fast_type>(0x55)};
+    constexpr fast_type b00110011{detail_::repbits<fast_type>(0x33)};
+    constexpr fast_type b00001111{detail_::repbits<fast_type>(0x0f)};
+    constexpr fast_type b00000001{detail_::repbits<fast_type>(0x01)};
+
+    fast_type v{fast_type{val} - ((fast_type{val} >> 1) & b01010101)};
+    v = (v & b00110011) + ((v >> 2) & b00110011);
+    v = (v + (v >> 4)) & b00001111;
+    return static_cast<int>(((v * b00000001) >> ((sizeof(T)-1)*8)) & 0xff);
+}
+
+#ifdef _WIN32
+
+template<typename T>
+inline std::enable_if_t<std::is_integral<T>::value && std::is_unsigned<T>::value
+    && std::numeric_limits<T>::digits <= 32,
+int> countr_zero(T v)
+{
+    unsigned long idx{std::numeric_limits<T>::digits};
+    _BitScanForward(&idx, static_cast<uint32_t>(v));
+    return static_cast<int>(idx);
+}
+
+template<typename T>
+inline std::enable_if_t<std::is_integral<T>::value && std::is_unsigned<T>::value
+    && 32 < std::numeric_limits<T>::digits && std::numeric_limits<T>::digits <= 64,
+int> countr_zero(T v)
+{
+    unsigned long idx{std::numeric_limits<T>::digits};
+#ifdef _WIN64
+    _BitScanForward64(&idx, v);
+#else
+    if(!_BitScanForward(&idx, static_cast<uint32_t>(v)))
+    {
+        if(_BitScanForward(&idx, static_cast<uint32_t>(v>>32)))
+            idx += 32;
+    }
+#endif /* _WIN64 */
+    return static_cast<int>(idx);
+}
+
+#else
+
+template<typename T>
+constexpr std::enable_if_t<std::is_integral<T>::value && std::is_unsigned<T>::value,
+int> countr_zero(T value)
+{ return popcount(static_cast<T>(~value & (value - 1))); }
+
+#endif
+#endif
+
+} // namespace al
+
+#endif /* AL_BIT_H */