2
2
mirror of https://github.com/octoleo/restic.git synced 2024-12-23 19:38:57 +00:00
restic/vendor/cloud.google.com/go/internal/fields/fold.go
2017-08-06 21:47:56 +02:00

157 lines
4.0 KiB
Go
Raw Blame History

This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

// Copyright 2016 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package fields
// This file was copied from https://go.googlesource.com/go/+/go1.7.3/src/encoding/json/fold.go.
// Only the license and package were changed.
import (
"bytes"
"unicode/utf8"
)
const (
caseMask = ^byte(0x20) // Mask to ignore case in ASCII.
kelvin = '\u212a'
smallLongEss = '\u017f'
)
// foldFunc returns one of four different case folding equivalence
// functions, from most general (and slow) to fastest:
//
// 1) bytes.EqualFold, if the key s contains any non-ASCII UTF-8
// 2) equalFoldRight, if s contains special folding ASCII ('k', 'K', 's', 'S')
// 3) asciiEqualFold, no special, but includes non-letters (including _)
// 4) simpleLetterEqualFold, no specials, no non-letters.
//
// The letters S and K are special because they map to 3 runes, not just 2:
// * S maps to s and to U+017F 'ſ' Latin small letter long s
// * k maps to K and to U+212A '' Kelvin sign
// See https://play.golang.org/p/tTxjOc0OGo
//
// The returned function is specialized for matching against s and
// should only be given s. It's not curried for performance reasons.
func foldFunc(s []byte) func(s, t []byte) bool {
nonLetter := false
special := false // special letter
for _, b := range s {
if b >= utf8.RuneSelf {
return bytes.EqualFold
}
upper := b & caseMask
if upper < 'A' || upper > 'Z' {
nonLetter = true
} else if upper == 'K' || upper == 'S' {
// See above for why these letters are special.
special = true
}
}
if special {
return equalFoldRight
}
if nonLetter {
return asciiEqualFold
}
return simpleLetterEqualFold
}
// equalFoldRight is a specialization of bytes.EqualFold when s is
// known to be all ASCII (including punctuation), but contains an 's',
// 'S', 'k', or 'K', requiring a Unicode fold on the bytes in t.
// See comments on foldFunc.
func equalFoldRight(s, t []byte) bool {
for _, sb := range s {
if len(t) == 0 {
return false
}
tb := t[0]
if tb < utf8.RuneSelf {
if sb != tb {
sbUpper := sb & caseMask
if 'A' <= sbUpper && sbUpper <= 'Z' {
if sbUpper != tb&caseMask {
return false
}
} else {
return false
}
}
t = t[1:]
continue
}
// sb is ASCII and t is not. t must be either kelvin
// sign or long s; sb must be s, S, k, or K.
tr, size := utf8.DecodeRune(t)
switch sb {
case 's', 'S':
if tr != smallLongEss {
return false
}
case 'k', 'K':
if tr != kelvin {
return false
}
default:
return false
}
t = t[size:]
}
if len(t) > 0 {
return false
}
return true
}
// asciiEqualFold is a specialization of bytes.EqualFold for use when
// s is all ASCII (but may contain non-letters) and contains no
// special-folding letters.
// See comments on foldFunc.
func asciiEqualFold(s, t []byte) bool {
if len(s) != len(t) {
return false
}
for i, sb := range s {
tb := t[i]
if sb == tb {
continue
}
if ('a' <= sb && sb <= 'z') || ('A' <= sb && sb <= 'Z') {
if sb&caseMask != tb&caseMask {
return false
}
} else {
return false
}
}
return true
}
// simpleLetterEqualFold is a specialization of bytes.EqualFold for
// use when s is all ASCII letters (no underscores, etc) and also
// doesn't contain 'k', 'K', 's', or 'S'.
// See comments on foldFunc.
func simpleLetterEqualFold(s, t []byte) bool {
if len(s) != len(t) {
return false
}
for i, b := range s {
if b&caseMask != t[i]&caseMask {
return false
}
}
return true
}