1 #pragma once
2
3 #include <charconv>
4 #include <iterator>
5 #include <string_view>
6
7 namespace details
8 {
9
10 // This implementation avoids the complexity of using std::isdigit, which pulls
11 // in all of <locale>, and likely has other consequences.
simpleIsDigit(const char c)12 inline bool simpleIsDigit(const char c)
13 {
14 return c >= '0' && c <= '9';
15 }
16
17 enum class ModeType
18 {
19 STRING,
20 NUMBER
21 };
22
23 } // namespace details
24
alphanumComp(std::string_view left,std::string_view right)25 inline int alphanumComp(std::string_view left, std::string_view right)
26 {
27 std::string_view::const_iterator l = left.cbegin();
28 std::string_view::const_iterator r = right.cbegin();
29
30 details::ModeType mode = details::ModeType::STRING;
31
32 while (l != left.end() && r != right.end())
33 {
34 if (mode == details::ModeType::STRING)
35 {
36 // check if this are digit characters
37 const bool lDigit = details::simpleIsDigit(*l);
38 const bool rDigit = details::simpleIsDigit(*r);
39 // if both characters are digits, we continue in NUMBER mode
40 if (lDigit && rDigit)
41 {
42 mode = details::ModeType::NUMBER;
43 continue;
44 }
45 // if only the left character is a digit, we have a result
46 if (lDigit)
47 {
48 return -1;
49 } // if only the right character is a digit, we have a result
50 if (rDigit)
51 {
52 return +1;
53 }
54 // compute the difference of both characters
55 const int diff = *l - *r;
56 // if they differ we have a result
57 if (diff != 0)
58 {
59 return diff;
60 }
61 // otherwise process the next characters
62 std::advance(l, 1);
63 std::advance(r, 1);
64 }
65 else // mode==NUMBER
66 {
67 // get the left number
68 int lInt = 0;
69 auto fc = std::from_chars(&(*l), &(*left.end()), lInt);
70 std::advance(l, std::distance(l, fc.ptr));
71
72 // get the right number
73 int rInt = 0;
74 fc = std::from_chars(&(*r), &(*right.end()), rInt);
75 std::advance(r, std::distance(r, fc.ptr));
76
77 // if the difference is not equal to zero, we have a comparison
78 // result
79 const int diff = lInt - rInt;
80 if (diff != 0)
81 {
82 return diff;
83 }
84
85 // otherwise we process the next substring in STRING mode
86 mode = details::ModeType::STRING;
87 }
88 }
89 if (r == right.end() && l == left.end())
90 {
91 return 0;
92 }
93 if (r == right.end())
94 {
95 return 1;
96 }
97 return -1;
98 }
99
100 // A generic template type compatible with std::less that can be used on generic
101 // containers (set, map, etc)
102 template <class Type>
103 struct AlphanumLess
104 {
operator ()AlphanumLess105 bool operator()(const Type& left, const Type& right) const
106 {
107 return alphanumComp(left, right) < 0;
108 }
109 };
110