50 lines
1.2 KiB
Go
50 lines
1.2 KiB
Go
// Copyright (C) 2017 The Syncthing Authors.
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//
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// This Source Code Form is subject to the terms of the Mozilla Public
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// License, v. 2.0. If a copy of the MPL was not distributed with this file,
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// You can obtain one at https://mozilla.org/MPL/2.0/.
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package fs
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import (
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"strings"
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"unicode"
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"unicode/utf8"
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"golang.org/x/text/unicode/norm"
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)
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// UnicodeLowercaseNormalized returns the Unicode lower case variant of s,
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// having also normalized it to normalization form C.
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func UnicodeLowercaseNormalized(s string) string {
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i := firstCaseChange(s)
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if i == -1 {
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return norm.NFC.String(s)
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}
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var rs strings.Builder
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// WriteRune always reserves utf8.UTFMax bytes for non-ASCII runes,
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// even if it doesn't need all that space. Overallocate now to prevent
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// it from ever triggering a reallocation.
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rs.Grow(utf8.UTFMax - 1 + len(s))
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rs.WriteString(s[:i])
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for _, r := range s[i:] {
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rs.WriteRune(unicode.ToLower(unicode.ToUpper(r)))
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}
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return norm.NFC.String(rs.String())
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}
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// Byte index of the first rune r s.t. lower(upper(r)) != r.
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func firstCaseChange(s string) int {
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for i, r := range s {
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if r <= unicode.MaxASCII && (r < 'A' || r > 'Z') {
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continue
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}
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if unicode.ToLower(unicode.ToUpper(r)) != r {
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return i
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}
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}
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return -1
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}
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