Zero.h

//------------------------------------------------------------------------------
/*
    This file is part of Beast: https://github.com/vinniefalco/Beast
    Copyright 2014, Tom Ritchford <tom@swirly.com>
 
    Permission to use, copy, modify, and/or distribute this software for any
    purpose  with  or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.
 
    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
//==============================================================================
 
#ifndef BEAST_UTILITY_ZERO_H_INCLUDED
#define BEAST_UTILITY_ZERO_H_INCLUDED
 
namespace beast {
 
struct Zero
{
    explicit Zero() = default;
};
 
namespace {
static constexpr Zero zero{};
}
 
template <typename T>
auto
signum(T const& t)
{
    return t.signum();
}
 
namespace detail {
namespace zero_helper {
 
// For argument dependent lookup to function properly, calls to signum must
// be made from a namespace that does not include overloads of the function..
template <class T>
auto
call_signum(T const& t)
{
    return signum(t);
}
 
}  // namespace zero_helper
}  // namespace detail
 
// Handle operators where T is on the left side using signum.
 
template <typename T>
bool
operator==(T const& t, Zero)
{
    return detail::zero_helper::call_signum(t) == 0;
}
 
template <typename T>
bool
operator!=(T const& t, Zero)
{
    return detail::zero_helper::call_signum(t) != 0;
}
 
template <typename T>
bool
operator<(T const& t, Zero)
{
    return detail::zero_helper::call_signum(t) < 0;
}
 
template <typename T>
bool
operator>(T const& t, Zero)
{
    return detail::zero_helper::call_signum(t) > 0;
}
 
template <typename T>
bool
operator>=(T const& t, Zero)
{
    return detail::zero_helper::call_signum(t) >= 0;
}
 
template <typename T>
bool
operator<=(T const& t, Zero)
{
    return detail::zero_helper::call_signum(t) <= 0;
}
 
// Handle operators where T is on the right side by
// reversing the operation, so that T is on the left side.
 
template <typename T>
bool
operator==(Zero, T const& t)
{
    return t == zero;
}
 
template <typename T>
bool
operator!=(Zero, T const& t)
{
    return t != zero;
}
 
template <typename T>
bool
operator<(Zero, T const& t)
{
    return t > zero;
}
 
template <typename T>
bool
operator>(Zero, T const& t)
{
    return t < zero;
}
 
template <typename T>
bool
operator>=(Zero, T const& t)
{
    return t <= zero;
}
 
template <typename T>
bool
operator<=(Zero, T const& t)
{
    return t >= zero;
}
 
}  // namespace beast
 
#endif