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#pragma once
#include <charconv>
#include <iterator>
#include <string_view>
namespace details
{
// This implementation avoids the complexity of using std::isdigit, which pulls
// in all of <locale>, and likely has other consequences.
inline bool simpleIsDigit(const char c)
{
return c >= '0' && c <= '9';
}
enum class ModeType
{
STRING,
NUMBER
};
} // namespace details
inline int alphanumComp(std::string_view left, std::string_view right)
{
std::string_view::const_iterator l = left.cbegin();
std::string_view::const_iterator r = right.cbegin();
details::ModeType mode = details::ModeType::STRING;
while (l != left.end() && r != right.end())
{
if (mode == details::ModeType::STRING)
{
// check if this are digit characters
const bool lDigit = details::simpleIsDigit(*l);
const bool rDigit = details::simpleIsDigit(*r);
// if both characters are digits, we continue in NUMBER mode
if (lDigit && rDigit)
{
mode = details::ModeType::NUMBER;
continue;
}
// if only the left character is a digit, we have a result
if (lDigit)
{
return -1;
} // if only the right character is a digit, we have a result
if (rDigit)
{
return +1;
}
// compute the difference of both characters
const int diff = *l - *r;
// if they differ we have a result
if (diff != 0)
{
return diff;
}
// otherwise process the next characters
std::advance(l, 1);
std::advance(r, 1);
}
else // mode==NUMBER
{
// get the left number
int lInt = 0;
auto fc = std::from_chars(&(*l), &(*left.end()), lInt);
std::advance(l, std::distance(l, fc.ptr));
// get the right number
int rInt = 0;
fc = std::from_chars(&(*r), &(*right.end()), rInt);
std::advance(r, std::distance(r, fc.ptr));
// if the difference is not equal to zero, we have a comparison
// result
const int diff = lInt - rInt;
if (diff != 0)
{
return diff;
}
// otherwise we process the next substring in STRING mode
mode = details::ModeType::STRING;
}
}
if (r == right.end() && l == left.end())
{
return 0;
}
if (r == right.end())
{
return 1;
}
return -1;
}
// A generic template type compatible with std::less that can be used on generic
// containers (set, map, etc)
template <class Type>
struct AlphanumLess
{
bool operator()(const Type& left, const Type& right) const
{
return alphanumComp(left, right) < 0;
}
};
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