srs/trunk/3rdparty/srt-1-fit/srtcore/utilities.h

/*
 * SRT - Secure, Reliable, Transport
 * Copyright (c) 2018 Haivision Systems Inc.
 * 
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 * 
 */

/*****************************************************************************
written by
   Haivision Systems Inc.
 *****************************************************************************/

#ifndef INC__SRT_UTILITIES_H
#define INC__SRT_UTILITIES_H


#ifdef __GNUG__
#define ATR_UNUSED __attribute__((unused))
#define ATR_DEPRECATED __attribute__((deprecated))
#else
#define ATR_UNUSED
#define ATR_DEPRECATED
#endif

#if defined(__cplusplus) && __cplusplus > 199711L
#define HAVE_CXX11 1

// For gcc 4.7, claim C++11 is supported, as long as experimental C++0x is on,
// however it's only the "most required C++11 support".
#if defined(__GXX_EXPERIMENTAL_CXX0X__) && __GNUC__ == 4 && __GNUC_MINOR__ >= 7 // 4.7 only!
#define ATR_NOEXCEPT
#define ATR_CONSTEXPR
#define ATR_OVERRIDE
#define ATR_FINAL
#else
#define HAVE_FULL_CXX11 1
#define ATR_NOEXCEPT noexcept
#define ATR_CONSTEXPR constexpr
#define ATR_OVERRIDE override
#define ATR_FINAL final
#endif

// Microsoft Visual Studio supports C++11, but not fully,
// and still did not change the value of __cplusplus. Treat
// this special way.
// _MSC_VER == 1800  means Microsoft Visual Studio 2013.
#elif defined(_MSC_VER) && _MSC_VER >= 1800
#define HAVE_CXX11 1
#if defined(_MSC_FULL_VER) && _MSC_FULL_VER >= 190023026
#define HAVE_FULL_CXX11 1
#define ATR_NOEXCEPT noexcept
#define ATR_CONSTEXPR constexpr
#define ATR_OVERRIDE override
#define ATR_FINAL final
#else
#define ATR_NOEXCEPT
#define ATR_CONSTEXPR
#define ATR_OVERRIDE
#define ATR_FINAL
#endif
#else
#define HAVE_CXX11 0
#define ATR_NOEXCEPT // throw() - bad idea
#define ATR_CONSTEXPR
#define ATR_OVERRIDE
#define ATR_FINAL

#endif

#if !HAVE_CXX11 && defined(REQUIRE_CXX11) && REQUIRE_CXX11 == 1
#error "The currently compiled application required C++11, but your compiler doesn't support it."
#endif


// Windows warning disabler
#define _CRT_SECURE_NO_WARNINGS 1

#include "platform_sys.h"

// Happens that these are defined, undefine them in advance
#undef min
#undef max

#include <string>
#include <algorithm>
#include <bitset>
#include <map>
#include <functional>
#include <memory>
#include <sstream>
#include <iomanip>

#if HAVE_CXX11
#include <type_traits>
#endif

#include <cstdlib>
#include <cerrno>
#include <cstring>

// -------------- UTILITIES ------------------------

// --- ENDIAN ---
// Copied from: https://gist.github.com/panzi/6856583
// License: Public Domain.

#if (defined(_WIN16) || defined(_WIN32) || defined(_WIN64)) && !defined(__WINDOWS__)

#	define __WINDOWS__

#endif

#if defined(__linux__) || defined(__CYGWIN__) || defined(__GNU__)

#	include <endian.h>

// GLIBC-2.8 and earlier does not provide these macros.
// See http://linux.die.net/man/3/endian
// From https://gist.github.com/panzi/6856583
#   if defined(__GLIBC__) \
      && ( !defined(__GLIBC_MINOR__) \
         || ((__GLIBC__ < 2) \
         || ((__GLIBC__ == 2) && (__GLIBC_MINOR__ < 9))) )
#       include <arpa/inet.h>
#       if defined(__BYTE_ORDER) && (__BYTE_ORDER == __LITTLE_ENDIAN)

#           define htole32(x) (x)
#           define le32toh(x) (x)

#       elif defined(__BYTE_ORDER) && (__BYTE_ORDER == __BIG_ENDIAN)

#           define htole16(x) ((((((uint16_t)(x)) >> 8))|((((uint16_t)(x)) << 8)))
#           define le16toh(x) ((((((uint16_t)(x)) >> 8))|((((uint16_t)(x)) << 8)))

#           define htole32(x) (((uint32_t)htole16(((uint16_t)(((uint32_t)(x)) >> 16)))) | (((uint32_t)htole16(((uint16_t)(x)))) << 16))
#           define le32toh(x) (((uint32_t)le16toh(((uint16_t)(((uint32_t)(x)) >> 16)))) | (((uint32_t)le16toh(((uint16_t)(x)))) << 16))

#       else
#           error Byte Order not supported or not defined.
#       endif
#   endif

#elif defined(__APPLE__)

#	include <libkern/OSByteOrder.h>

#	define htobe16(x) OSSwapHostToBigInt16(x)
#	define htole16(x) OSSwapHostToLittleInt16(x)
#	define be16toh(x) OSSwapBigToHostInt16(x)
#	define le16toh(x) OSSwapLittleToHostInt16(x)
 
#	define htobe32(x) OSSwapHostToBigInt32(x)
#	define htole32(x) OSSwapHostToLittleInt32(x)
#	define be32toh(x) OSSwapBigToHostInt32(x)
#	define le32toh(x) OSSwapLittleToHostInt32(x)
 
#	define htobe64(x) OSSwapHostToBigInt64(x)
#	define htole64(x) OSSwapHostToLittleInt64(x)
#	define be64toh(x) OSSwapBigToHostInt64(x)
#	define le64toh(x) OSSwapLittleToHostInt64(x)

#	define __BYTE_ORDER    BYTE_ORDER
#	define __BIG_ENDIAN    BIG_ENDIAN
#	define __LITTLE_ENDIAN LITTLE_ENDIAN
#	define __PDP_ENDIAN    PDP_ENDIAN

#elif defined(__OpenBSD__)

#	include <sys/endian.h>

#elif defined(__NetBSD__) || defined(__FreeBSD__) || defined(__DragonFly__)

#	include <sys/endian.h>

#ifndef be16toh
#	define be16toh(x) betoh16(x)
#endif
#ifndef le16toh
#	define le16toh(x) letoh16(x)
#endif

#ifndef be32toh
#	define be32toh(x) betoh32(x)
#endif
#ifndef le32toh
#	define le32toh(x) letoh32(x)
#endif

#ifndef be64toh
#	define be64toh(x) betoh64(x)
#endif
#ifndef le64toh
#	define le64toh(x) letoh64(x)
#endif

#elif defined(__WINDOWS__)

#	include <winsock2.h>

#	if BYTE_ORDER == LITTLE_ENDIAN

#		define htobe16(x) htons(x)
#		define htole16(x) (x)
#		define be16toh(x) ntohs(x)
#		define le16toh(x) (x)
 
#		define htobe32(x) htonl(x)
#		define htole32(x) (x)
#		define be32toh(x) ntohl(x)
#		define le32toh(x) (x)
 
#		define htobe64(x) htonll(x)
#		define htole64(x) (x)
#		define be64toh(x) ntohll(x)
#		define le64toh(x) (x)

#	elif BYTE_ORDER == BIG_ENDIAN

		/* that would be xbox 360 */
#		define htobe16(x) (x)
#		define htole16(x) __builtin_bswap16(x)
#		define be16toh(x) (x)
#		define le16toh(x) __builtin_bswap16(x)
 
#		define htobe32(x) (x)
#		define htole32(x) __builtin_bswap32(x)
#		define be32toh(x) (x)
#		define le32toh(x) __builtin_bswap32(x)
 
#		define htobe64(x) (x)
#		define htole64(x) __builtin_bswap64(x)
#		define be64toh(x) (x)
#		define le64toh(x) __builtin_bswap64(x)

#	else

#		error byte order not supported

#	endif

#	define __BYTE_ORDER    BYTE_ORDER
#	define __BIG_ENDIAN    BIG_ENDIAN
#	define __LITTLE_ENDIAN LITTLE_ENDIAN
#	define __PDP_ENDIAN    PDP_ENDIAN

#else

#	error Endian: platform not supported

#endif

// Hardware <--> Network (big endian) convention
inline void HtoNLA(uint32_t* dst, const uint32_t* src, size_t size)
{
    for (size_t i = 0; i < size; ++ i)
        dst[i] = htonl(src[i]);
}

inline void NtoHLA(uint32_t* dst, const uint32_t* src, size_t size)
{
    for (size_t i = 0; i < size; ++ i)
        dst[i] = ntohl(src[i]);
}

// Hardware <--> Intel (little endian) convention
inline void HtoILA(uint32_t* dst, const uint32_t* src, size_t size)
{
    for (size_t i = 0; i < size; ++ i)
        dst[i] = htole32(src[i]);
}

inline void ItoHLA(uint32_t* dst, const uint32_t* src, size_t size)
{
    for (size_t i = 0; i < size; ++ i)
        dst[i] = le32toh(src[i]);
}

// Bit numbering utility.
//
// This is something that allows you to turn 32-bit integers into bit fields.
// Although bitfields are part of C++ language, they are not designed to be
// interchanged with 32-bit numbers, and any attempt to doing it (by placing
// inside a union, for example) is nonportable (order of bitfields inside
// same-covering 32-bit integer number is dependent on the endian), so they are
// popularly disregarded as useless. Instead the 32-bit numbers with bits
// individually selected is preferred, with usually manual playing around with
// & and | operators, as well as << and >>. This tool is designed to simplify
// the use of them. This can be used to qualify a range of bits inside a 32-bit
// number to be a separate number, you can "wrap" it by placing the integer
// value in the range of these bits, as well as "unwrap" (extract) it from
// the given place. For your own safety, use one prefix to all constants that
// concern bit ranges intended to be inside the same "bit container".
//
// Usage: typedef Bits<leftmost, rightmost> MASKTYPE;  // MASKTYPE is a name of your choice.
//
// With this defined, you can use the following members:
// - MASKTYPE::mask - to get the int32_t value with bimask (used bits set to 1, others to 0)
// - MASKTYPE::offset - to get the lowermost bit number, or number of bits to shift
// - MASKTYPE::wrap(int value) - to create a bitset where given value is encoded in given bits
// - MASKTYPE::unwrap(int bitset) - to extract an integer value from the bitset basing on mask definition
// (rightmost defaults to leftmost)
// REMEMBER: leftmost > rightmost because bit 0 is the LEAST significant one!

template <size_t L, size_t R, bool parent_correct = true>
struct BitsetMask
{
    static const bool correct = L >= R;
    static const uint32_t value = (1u << L) | BitsetMask<L-1, R, correct>::value;
};

// This is kind-of functional programming. This describes a special case that is
// a "terminal case" in case when decreased L-1 (see above) reached == R.
template<size_t R>
struct BitsetMask<R, R, true>
{
    static const bool correct = true;
    static const uint32_t value = 1 << R;
};

// This is a trap for a case that BitsetMask::correct in the master template definition
// evaluates to false. This trap causes compile error and prevents from continuing
// recursive unwinding in wrong direction (and challenging the compiler's resistiveness
// for infinite loops).
template <size_t L, size_t R>
struct BitsetMask<L, R, false>
{
};

template <size_t L, size_t R = L>
struct Bits
{
    // DID YOU GET a kind-of error: 'mask' is not a member of 'Bits<3u, 5u, false>'?
    // See the the above declaration of 'correct'!
    static const uint32_t mask = BitsetMask<L, R>::value;
    static const uint32_t offset = R;
    static const size_t size = L - R + 1;

    // Example: if our bitset mask is 00111100, this checks if given value fits in
    // 00001111 mask (that is, does not exceed <0, 15>.
    static bool fit(uint32_t value) { return (BitsetMask<L-R, 0>::value & value) == value; }

    /// 'wrap' gets some given value that should be placed in appropriate bit range and
    /// returns a whole 32-bit word that has the value already at specified place.
    /// To create a 32-bit container that contains already all values destined for different
    /// bit ranges, simply use wrap() for each of them and bind them with | operator.
    static uint32_t wrap(uint32_t baseval) { return (baseval << offset) & mask; }

    /// Extracts appropriate bit range and returns them as normal integer value.
    static uint32_t unwrap(uint32_t bitset) { return (bitset & mask) >> offset; }

    template<class T>
    static T unwrapt(uint32_t bitset) { return static_cast<T>(unwrap(bitset)); }
};


//inline int32_t Bit(size_t b) { return 1 << b; }
// XXX This would work only with 'constexpr', but this is
// available only in C++11. In C++03 this can be only done
// using a macro.
//
// Actually this can be expressed in C++11 using a better technique,
// such as user-defined literals:
// 2_bit  --> 1 >> 2

#ifdef BIT
#undef BIT
#endif
#define BIT(x) (1 << (x))


// ------------------------------------------------------------
// This is something that reminds a structure consisting of fields
// of the same type, implemented as an array. It's parametrized
// by the type of fields and the type, which's values should be
// used for indexing (preferably an enum type). Whatever type is
// used for indexing, it is converted to size_t for indexing the
// actual array.
// 
// The user should use it as an array: ds[DS_NAME], stating
// that DS_NAME is of enum type passed as 3rd parameter.
// However trying to do ds[0] would cause a compile error.
template <typename FieldType, size_t NoOfFields, typename IndexerType>
struct DynamicStruct
{
    FieldType inarray[NoOfFields];

    void clear()
    {
        // As a standard library, it can be believed that this call
        // can be optimized when FieldType is some integer.
        std::fill(inarray, inarray + NoOfFields, FieldType());
    }

    FieldType operator[](IndexerType ix) const { return inarray[size_t(ix)]; }
    FieldType& operator[](IndexerType ix) { return inarray[size_t(ix)]; }

    template<class AnyOther>
    FieldType operator[](AnyOther ix) const
    {
        // If you can see a compile error here ('int' is not a class or struct, or
        // that there's no definition of 'type' in given type), it means that you
        // have used invalid data type passed to [] operator. See the definition
        // of this type as DynamicStruct and see which type is required for indexing.
        typename AnyOther::type wrong_usage_of_operator_index = AnyOther::type;
        return inarray[size_t(ix)];
    }

    template<class AnyOther>
    FieldType& operator[](AnyOther ix)
    {
        // If you can see a compile error here ('int' is not a class or struct, or
        // that there's no definition of 'type' in given type), it means that you
        // have used invalid data type passed to [] operator. See the definition
        // of this type as DynamicStruct and see which type is required for indexing.
        typename AnyOther::type wrong_usage_of_operator_index = AnyOther::type;
        return inarray[size_t(ix)];
    }

    operator FieldType* () { return inarray; }
    operator const FieldType* () const { return inarray; }

    char* raw() { return (char*)inarray; }
};


// ------------------------------------------------------------



inline bool IsSet(int32_t bitset, int32_t flagset)
{
    return (bitset & flagset) == flagset;
}

// Homecooked version of ref_t. It's a copy of std::reference_wrapper
// voided of unwanted properties and renamed to ref_t.


#if HAVE_CXX11
#include <functional>
#endif

template<typename Type>
class ref_t
{
    Type* m_data;

public:
    typedef Type type;

#if HAVE_CXX11
    explicit ref_t(Type& __indata)
        : m_data(std::addressof(__indata))
        { }
#else
    explicit ref_t(Type& __indata)
        : m_data((Type*)(&(char&)(__indata)))
        { }
#endif

    ref_t(const ref_t<Type>& inref)
        : m_data(inref.m_data)
    { }

#if HAVE_CXX11
    ref_t(const std::reference_wrapper<Type>& i): m_data(std::addressof(i.get())) {}
#endif

    Type& operator*() { return *m_data; }

    Type& get() const
    { return *m_data; }

    Type operator->() const
    { return *m_data; }
};

// This is required for Printable function if you have a container of pairs,
// but this function has a different definition for C++11 and C++03.
namespace srt_pair_op
{
    template <class Value1, class Value2>
    std::ostream& operator<<(std::ostream& s, const std::pair<Value1, Value2>& v)
    {
        s << "{" << v.first << " " << v.second << "}";
        return s;
    }
}

#if HAVE_CXX11

// This alias was created so that 'Ref' (not 'ref') is used everywhere.
// Normally the C++11 'ref' fits perfectly here, however in C++03 mode
// it would have to be newly created. This would then cause a conflict
// between C++03 SRT and C++11 applications as well as between C++ standard
// library and SRT when SRT is compiled in C++11 mode (as it happens on
// Darwin/clang).
template <class In>
inline auto Ref(In& i) -> decltype(std::ref(i)) { return std::ref(i); }

template <class In>
inline auto Move(In& i) -> decltype(std::move(i)) { return std::move(i); }

// Gluing string of any type, wrapper for operator <<

template <class Stream>
inline Stream& Print(Stream& in) { return in;}

template <class Stream, class Arg1, class... Args>
inline Stream& Print(Stream& sout, Arg1&& arg1, Args&&... args)
{
    sout << arg1;
    return Print(sout, args...);
}

template <class... Args>
inline std::string Sprint(Args&&... args)
{
    std::ostringstream sout;
    Print(sout, args...);
    return sout.str();
}

// We need to use UniquePtr, in the form of C++03 it will be a #define.
// Naturally will be used std::move() so that it can later painlessly
// switch to C++11.
template <class T>
using UniquePtr = std::unique_ptr<T>;

// Some utilities borrowed from tumux, as this is using options
// similar way.
template <class Container, class Value = typename Container::value_type, typename... Args> inline
std::string Printable(const Container& in, Value /*pseudoargument*/, Args&&... args)
{
    using namespace srt_pair_op;
    std::ostringstream os;
    Print(os, args...);
    os << "[ ";
    for (auto i: in)
        os << Value(i) << " ";
    os << "]";
    return os.str();
}

template <class Container> inline
std::string Printable(const Container& in)
{
    using namespace srt_pair_op;
    using Value = typename Container::value_type;
    return Printable(in, Value());
}

template<typename Map, typename Key>
auto map_get(Map& m, const Key& key, typename Map::mapped_type def = typename Map::mapped_type()) -> typename Map::mapped_type
{
    auto it = m.find(key);
    return it == m.end() ? def : it->second;
}

template<typename Map, typename Key>
auto map_getp(Map& m, const Key& key) -> typename Map::mapped_type*
{
    auto it = m.find(key);
    return it == m.end() ? nullptr : std::addressof(it->second);
}

template<typename Map, typename Key>
auto map_getp(const Map& m, const Key& key) -> typename Map::mapped_type const*
{
    auto it = m.find(key);
    return it == m.end() ? nullptr : std::addressof(it->second);
}


#else

template <class Type>
ref_t<Type> Ref(Type& arg)
{
    return ref_t<Type>(arg);
}

// The unique_ptr requires C++11, and the rvalue-reference feature,
// so here we're simulate the behavior using the old std::auto_ptr.

// This is only to make a "move" call transparent and look ok towards
// the C++11 code.
template <class T>
std::auto_ptr_ref<T> Move(const std::auto_ptr_ref<T>& in) { return in; }

// We need to provide also some fixes for this type that were not present in auto_ptr,
// but they are present in unique_ptr.

// C++03 doesn't have a templated typedef, but still we need some things
// that can only function as a class.
template <class T>
class UniquePtr: public std::auto_ptr<T>
{
    typedef std::auto_ptr<T> Base;

public:

    // This is a template - so method names must be declared explicitly
    typedef typename Base::element_type element_type;
    using Base::get;
    using Base::reset;

    // All constructor declarations must be repeated.
    // "Constructor delegation" is also only C++11 feature.
    explicit UniquePtr(element_type* __p = 0) throw() : Base(__p) {}
    UniquePtr(UniquePtr& __a) throw() : Base(__a) { }
    template<typename _Tp1>
    UniquePtr(UniquePtr<_Tp1>& __a) throw() : Base(__a) {}

    UniquePtr& operator=(UniquePtr& __a) throw() { return Base::operator=(__a); }
    template<typename _Tp1>
    UniquePtr& operator=(UniquePtr<_Tp1>& __a) throw() { return Base::operator=(__a); }

    // Good, now we need to add some parts of the API of unique_ptr.

    bool operator==(const UniquePtr& two) const { return get() == two.get(); }
    bool operator!=(const UniquePtr& two) const { return get() != two.get(); }

    bool operator==(const element_type* two) const { return get() == two; }
    bool operator!=(const element_type* two) const { return get() != two; }

    operator bool () { return 0!= get(); }
};

// A primitive one-argument version of Printable
template <class Container> inline
std::string Printable(const Container& in)
{
    using namespace srt_pair_op;
    typedef typename Container::value_type Value;
    std::ostringstream os;
    os << "[ ";
    for (typename Container::const_iterator i = in.begin(); i != in.end(); ++i)
        os << Value(*i) << " ";
    os << "]";

    return os.str();
}

template<typename Map, typename Key>
typename Map::mapped_type map_get(Map& m, const Key& key, typename Map::mapped_type def = typename Map::mapped_type())
{
    typename Map::iterator it = m.find(key);
    return it == m.end() ? def : it->second;
}

template<typename Map, typename Key>
typename Map::mapped_type map_get(const Map& m, const Key& key, typename Map::mapped_type def = typename Map::mapped_type())
{
    typename Map::const_iterator it = m.find(key);
    return it == m.end() ? def : it->second;
}

template<typename Map, typename Key>
typename Map::mapped_type* map_getp(Map& m, const Key& key)
{
    typename Map::iterator it = m.find(key);
    return it == m.end() ? (typename Map::mapped_type*)0 : &(it->second);
}

template<typename Map, typename Key>
typename Map::mapped_type const* map_getp(const Map& m, const Key& key)
{
    typename Map::const_iterator it = m.find(key);
    return it == m.end() ? (typename Map::mapped_type*)0 : &(it->second);
}

#endif

template <class Signature>
struct CallbackHolder
{
    void* opaque;
    Signature* fn;

    CallbackHolder(): opaque(NULL), fn(NULL)  {}

    void set(void* o, Signature* f)
    {
        // Test if the pointer is a pointer to function. Don't let
        // other type of pointers here.
#if HAVE_CXX11
        static_assert(std::is_function<Signature>::value, "CallbackHolder is for functions only!");
#else
        // This is a poor-man's replacement, which should in most compilers
        // generate a warning, if `Signature` resolves to a value type.
        // This would make an illegal pointer cast from a value to a function type.
        // Casting function-to-function, however, should not. Unfortunately
        // newer compilers disallow that, too (when a signature differs), but
        // then they should better use the C++11 way, much more reliable and safer.
        void* (*testfn)(void*) ATR_UNUSED = (void*(*)(void*))f;
#endif
        opaque = o;
        fn = f;
    }

    operator bool() { return fn != NULL; }
};

#define CALLBACK_CALL(holder,...) (*holder.fn)(holder.opaque, __VA_ARGS__)

inline std::string FormatBinaryString(const uint8_t* bytes, size_t size)
{
    if ( size == 0 )
        return "";

    //char buf[256];
    using namespace std;

    ostringstream os;

    // I know, it's funny to use sprintf and ostringstream simultaneously,
    // but " %02X" in iostream is: << " " << hex << uppercase << setw(2) << setfill('0') << VALUE << setw(1)
    // Too noisy. OTOH ostringstream solves the problem of memory allocation
    // for a string of unpredictable size.
    //sprintf(buf, "%02X", int(bytes[0]));

    os.fill('0');
    os.width(2);
    os.setf(ios::basefield, ios::hex);
    os.setf(ios::uppercase);

    //os << buf;
    os << int(bytes[0]);


    for (size_t i = 1; i < size; ++i)
    {
        //sprintf(buf, " %02X", int(bytes[i]));
        //os << buf;
        os << int(bytes[i]);
    }
    return os.str();
}


/// This class is useful in every place where
/// the time drift should be traced. It's currently in use in every
/// solution that implements any kind of TSBPD.
template<unsigned MAX_SPAN, int MAX_DRIFT, bool CLEAR_ON_UPDATE = true>
class DriftTracer
{
    int64_t  m_qDrift;
    int64_t  m_qOverdrift;

    int64_t  m_qDriftSum;
    unsigned m_uDriftSpan;

public:
    DriftTracer()
        : m_qDrift(0)
        , m_qOverdrift(0)
        , m_qDriftSum(0)
        , m_uDriftSpan(0)
    {}

    bool update(int64_t driftval)
    {
        m_qDriftSum += driftval;
        ++m_uDriftSpan;

        if (m_uDriftSpan < MAX_SPAN)
            return false;

        if (CLEAR_ON_UPDATE)
            m_qOverdrift = 0;

        // Calculate the median of all drift values.
        // In most cases, the divisor should be == MAX_SPAN.
        m_qDrift = m_qDriftSum / m_uDriftSpan;

        // And clear the collection
        m_qDriftSum = 0;
        m_uDriftSpan = 0;

        // In case of "overdrift", save the overdriven value in 'm_qOverdrift'.
        // In clear mode, you should add this value to the time base when update()
        // returns true. The drift value will be since now measured with the
        // overdrift assumed to be added to the base.
        if (std::abs(m_qDrift) > MAX_DRIFT)
        {
            m_qOverdrift = m_qDrift < 0 ? -MAX_DRIFT : MAX_DRIFT;
            m_qDrift -= m_qOverdrift;
        }

        // printDriftOffset(m_qOverdrift, m_qDrift);

        // Timebase is separate
        // m_qTimeBase += m_qOverdrift;

        return true;
    }

    // These values can be read at any time, however if you want
    // to depend on the fact that they have been changed lately,
    // you have to check the return value from update().
    //
    // IMPORTANT: drift() can be called at any time, just remember
    // that this value may look different than before only if the
    // last update() returned true, which need not be important for you.
    //
    // CASE: CLEAR_ON_UPDATE = true
    // overdrift() should be read only immediately after update() returned
    // true. It will stay available with this value until the next time when
    // update() returns true, in which case the value will be cleared.
    // Therefore, after calling update() if it retuns true, you should read
    // overdrift() immediately an make some use of it. Next valid overdrift
    // will be then relative to every previous overdrift.
    //
    // CASE: CLEAR_ON_UPDATE = false
    // overdrift() will start from 0, but it will always keep track on
    // any changes in overdrift. By manipulating the MAX_DRIFT parameter
    // you can decide how high the drift can go relatively to stay below
    // overdrift.
    int64_t drift() const { return m_qDrift; }
    int64_t overdrift() const { return m_qOverdrift; }
};

template <class KeyType, class ValueType>
struct MapProxy
{
    std::map<KeyType, ValueType>& mp;
    const KeyType& key;

    MapProxy(std::map<KeyType, ValueType>& m, const KeyType& k): mp(m), key(k) {}

    void operator=(const ValueType& val)
    {
        mp[key] = val;
    }

    typename std::map<KeyType, ValueType>::iterator find()
    {
        return mp.find(key);
    }

    typename std::map<KeyType, ValueType>::const_iterator find() const
    {
        return mp.find(key);
    }

    operator ValueType() const
    {
        typename std::map<KeyType, ValueType>::const_iterator p = find();
        if (p == mp.end())
            return "";
        return p->second;
    }

    ValueType deflt(const ValueType& defval) const
    {
        typename std::map<KeyType, ValueType>::const_iterator p = find();
        if (p == mp.end())
            return defval;
        return p->second;
    }

    bool exists() const
    {
        return find() != mp.end();
    }
};

inline std::string BufferStamp(const char* mem, size_t size)
{
    using namespace std;
    char spread[16];

    int n = 16-size;
    if (n > 0)
        memset(spread+16-n, 0, n);
    memcpy(spread, mem, min(size_t(16), size));

    // Now prepare 4 cells for uint32_t.
    union
    {
        uint32_t sum;
        char cells[4];
    };
    memset(cells, 0, 4);

    for (size_t x = 0; x < 4; ++x)
        for (size_t y = 0; y < 4; ++y)
        {
            cells[x] += spread[x+4*y];
        }

    // Convert to hex string

    ostringstream os;

    os << hex << uppercase << setfill('0') << setw(8) << sum;

    return os.str();
}

template <class OutputIterator>
inline void Split(const std::string & str, char delimiter, OutputIterator tokens)
{
    if ( str.empty() )
        return; // May cause crash and won't extract anything anyway

    std::size_t start;
    std::size_t end = -1;

    do
    {
        start = end + 1;
        end = str.find(delimiter, start);
        *tokens = str.substr(
                start,
                (end == std::string::npos) ? std::string::npos : end - start);
        ++tokens;
    } while (end != std::string::npos);
}

inline std::string SelectNot(const std::string& unwanted, const std::string& s1, const std::string& s2)
{
    if (s1 == unwanted)
        return s2; // might be unwanted, too, but then, there's nothing you can do anyway
    if (s2 == unwanted)
        return s1;

    // Both have wanted values, so now compare if they are same
    if (s1 == s2)
        return s1; // occasionally there's a winner

    // Irresolvable situation.
    return std::string();
}

inline std::string SelectDefault(const std::string& checked, const std::string& def)
{
    if (checked == "")
        return def;
    return checked;
}

template <class It>
inline size_t safe_advance(It& it, size_t num, It end)
{
    while ( it != end && num )
    {
        --num;
        ++it;
    }

    return num; // will be effectively 0, if reached the required point, or >0, if end was by that number earlier
}

// This is available only in C++17, dunno why not C++11 as it's pretty useful.
template <class V, size_t N> inline
ATR_CONSTEXPR size_t Size(const V (&)[N]) ATR_NOEXCEPT { return N; }

template <size_t DEPRLEN, typename ValueType>
inline ValueType avg_iir(ValueType old_value, ValueType new_value)
{
    return (old_value*(DEPRLEN-1) + new_value)/DEPRLEN;
}

#endif