compare_strings.go (2207B)
1 // Copyright 2019 The Hugo Authors. All rights reserved.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 // http://www.apache.org/licenses/LICENSE-2.0
7 //
8 // Unless required by applicable law or agreed to in writing, software
9 // distributed under the License is distributed on an "AS IS" BASIS,
10 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
11 // See the License for the specific language governing permissions and
12 // limitations under the License.
13
14 package compare
15
16 import (
17 "strings"
18 "unicode"
19 "unicode/utf8"
20 )
21
22 // Strings returns an integer comparing two strings lexicographically.
23 func Strings(s, t string) int {
24 c := compareFold(s, t)
25
26 if c == 0 {
27 // "B" and "b" would be the same so we need a tiebreaker.
28 return strings.Compare(s, t)
29 }
30
31 return c
32 }
33
34 // This function is derived from strings.EqualFold in Go's stdlib.
35 // https://github.com/golang/go/blob/ad4a58e31501bce5de2aad90a620eaecdc1eecb8/src/strings/strings.go#L893
36 func compareFold(s, t string) int {
37 for s != "" && t != "" {
38 var sr, tr rune
39 if s[0] < utf8.RuneSelf {
40 sr, s = rune(s[0]), s[1:]
41 } else {
42 r, size := utf8.DecodeRuneInString(s)
43 sr, s = r, s[size:]
44 }
45 if t[0] < utf8.RuneSelf {
46 tr, t = rune(t[0]), t[1:]
47 } else {
48 r, size := utf8.DecodeRuneInString(t)
49 tr, t = r, t[size:]
50 }
51
52 if tr == sr {
53 continue
54 }
55
56 c := 1
57 if tr < sr {
58 tr, sr = sr, tr
59 c = -c
60 }
61
62 // ASCII only.
63 if tr < utf8.RuneSelf {
64 if sr >= 'A' && sr <= 'Z' {
65 if tr <= 'Z' {
66 // Same case.
67 return -c
68 }
69
70 diff := tr - (sr + 'a' - 'A')
71
72 if diff == 0 {
73 continue
74 }
75
76 if diff < 0 {
77 return c
78 }
79
80 if diff > 0 {
81 return -c
82 }
83 }
84 }
85
86 // Unicode.
87 r := unicode.SimpleFold(sr)
88 for r != sr && r < tr {
89 r = unicode.SimpleFold(r)
90 }
91
92 if r == tr {
93 continue
94 }
95
96 return -c
97 }
98
99 if s == "" && t == "" {
100 return 0
101 }
102
103 if s == "" {
104 return -1
105 }
106
107 return 1
108 }
109
110 // LessStrings returns whether s is less than t lexicographically.
111 func LessStrings(s, t string) bool {
112 return Strings(s, t) < 0
113 }