mirror of
https://github.com/schollz/cowyo.git
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144 lines
3.4 KiB
Go
144 lines
3.4 KiB
Go
// Copyright 2013 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package json
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import (
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"bytes"
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"unicode/utf8"
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)
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const (
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caseMask = ^byte(0x20) // Mask to ignore case in ASCII.
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kelvin = '\u212a'
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smallLongEss = '\u017f'
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)
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// foldFunc returns one of four different case folding equivalence
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// functions, from most general (and slow) to fastest:
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//
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// 1) bytes.EqualFold, if the key s contains any non-ASCII UTF-8
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// 2) equalFoldRight, if s contains special folding ASCII ('k', 'K', 's', 'S')
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// 3) asciiEqualFold, no special, but includes non-letters (including _)
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// 4) simpleLetterEqualFold, no specials, no non-letters.
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//
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// The letters S and K are special because they map to 3 runes, not just 2:
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// * S maps to s and to U+017F 'ſ' Latin small letter long s
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// * k maps to K and to U+212A 'K' Kelvin sign
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// See https://play.golang.org/p/tTxjOc0OGo
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//
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// The returned function is specialized for matching against s and
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// should only be given s. It's not curried for performance reasons.
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func foldFunc(s []byte) func(s, t []byte) bool {
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nonLetter := false
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special := false // special letter
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for _, b := range s {
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if b >= utf8.RuneSelf {
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return bytes.EqualFold
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}
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upper := b & caseMask
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if upper < 'A' || upper > 'Z' {
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nonLetter = true
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} else if upper == 'K' || upper == 'S' {
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// See above for why these letters are special.
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special = true
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}
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}
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if special {
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return equalFoldRight
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}
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if nonLetter {
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return asciiEqualFold
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}
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return simpleLetterEqualFold
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}
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// equalFoldRight is a specialization of bytes.EqualFold when s is
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// known to be all ASCII (including punctuation), but contains an 's',
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// 'S', 'k', or 'K', requiring a Unicode fold on the bytes in t.
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// See comments on foldFunc.
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func equalFoldRight(s, t []byte) bool {
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for _, sb := range s {
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if len(t) == 0 {
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return false
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}
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tb := t[0]
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if tb < utf8.RuneSelf {
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if sb != tb {
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sbUpper := sb & caseMask
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if 'A' <= sbUpper && sbUpper <= 'Z' {
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if sbUpper != tb&caseMask {
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return false
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}
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} else {
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return false
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}
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}
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t = t[1:]
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continue
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}
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// sb is ASCII and t is not. t must be either kelvin
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// sign or long s; sb must be s, S, k, or K.
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tr, size := utf8.DecodeRune(t)
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switch sb {
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case 's', 'S':
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if tr != smallLongEss {
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return false
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}
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case 'k', 'K':
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if tr != kelvin {
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return false
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}
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default:
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return false
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}
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t = t[size:]
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}
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if len(t) > 0 {
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return false
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}
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return true
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}
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// asciiEqualFold is a specialization of bytes.EqualFold for use when
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// s is all ASCII (but may contain non-letters) and contains no
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// special-folding letters.
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// See comments on foldFunc.
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func asciiEqualFold(s, t []byte) bool {
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if len(s) != len(t) {
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return false
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}
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for i, sb := range s {
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tb := t[i]
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if sb == tb {
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continue
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}
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if ('a' <= sb && sb <= 'z') || ('A' <= sb && sb <= 'Z') {
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if sb&caseMask != tb&caseMask {
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return false
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}
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} else {
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return false
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}
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}
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return true
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}
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// simpleLetterEqualFold is a specialization of bytes.EqualFold for
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// use when s is all ASCII letters (no underscores, etc) and also
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// doesn't contain 'k', 'K', 's', or 'S'.
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// See comments on foldFunc.
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func simpleLetterEqualFold(s, t []byte) bool {
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if len(s) != len(t) {
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return false
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}
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for i, b := range s {
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if b&caseMask != t[i]&caseMask {
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return false
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}
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}
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return true
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}
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