1 // Copyright 2013 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
13 caseMask
= ^byte(0x20) // Mask to ignore case in ASCII.
15 smallLongEss
= '\u017f'
18 // foldFunc returns one of four different case folding equivalence
19 // functions, from most general (and slow) to fastest:
21 // 1) bytes.EqualFold, if the key s contains any non-ASCII UTF-8
22 // 2) equalFoldRight, if s contains special folding ASCII ('k', 'K', 's', 'S')
23 // 3) asciiEqualFold, no special, but includes non-letters (including _)
24 // 4) simpleLetterEqualFold, no specials, no non-letters.
26 // The letters S and K are special because they map to 3 runes, not just 2:
27 // * S maps to s and to U+017F 'ſ' Latin small letter long s
28 // * k maps to K and to U+212A 'K' Kelvin sign
29 // See https://play.golang.org/p/tTxjOc0OGo
31 // The returned function is specialized for matching against s and
32 // should only be given s. It's not curried for performance reasons.
33 func foldFunc(s
[]byte) func(s
, t
[]byte) bool {
35 special
:= false // special letter
37 if b
>= utf8
.RuneSelf
{
38 return bytes
.EqualFold
41 if upper
< 'A' || upper
> 'Z' {
43 } else if upper
== 'K' || upper
== 'S' {
44 // See above for why these letters are special.
54 return simpleLetterEqualFold
57 // equalFoldRight is a specialization of bytes.EqualFold when s is
58 // known to be all ASCII (including punctuation), but contains an 's',
59 // 'S', 'k', or 'K', requiring a Unicode fold on the bytes in t.
60 // See comments on foldFunc.
61 func equalFoldRight(s
, t
[]byte) bool {
62 for _
, sb
:= range s
{
67 if tb
< utf8
.RuneSelf
{
69 sbUpper
:= sb
& caseMask
70 if 'A' <= sbUpper
&& sbUpper
<= 'Z' {
71 if sbUpper
!= tb
&caseMask
{
81 // sb is ASCII and t is not. t must be either kelvin
82 // sign or long s; sb must be s, S, k, or K.
83 tr
, size
:= utf8
.DecodeRune(t
)
86 if tr
!= smallLongEss
{
105 // asciiEqualFold is a specialization of bytes.EqualFold for use when
106 // s is all ASCII (but may contain non-letters) and contains no
107 // special-folding letters.
108 // See comments on foldFunc.
109 func asciiEqualFold(s
, t
[]byte) bool {
110 if len(s
) != len(t
) {
113 for i
, sb
:= range s
{
118 if ('a' <= sb
&& sb
<= 'z') ||
('A' <= sb
&& sb
<= 'Z') {
119 if sb
&caseMask
!= tb
&caseMask
{
129 // simpleLetterEqualFold is a specialization of bytes.EqualFold for
130 // use when s is all ASCII letters (no underscores, etc) and also
131 // doesn't contain 'k', 'K', 's', or 'S'.
132 // See comments on foldFunc.
133 func simpleLetterEqualFold(s
, t
[]byte) bool {
134 if len(s
) != len(t
) {
137 for i
, b
:= range s
{
138 if b
&caseMask
!= t
[i
]&caseMask
{