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Source file src/strings/strings.go

     1	// Copyright 2009 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.
     4	
     5	// Package strings implements simple functions to manipulate UTF-8 encoded strings.
     6	//
     7	// For information about UTF-8 strings in Go, see https://blog.golang.org/strings.
     8	package strings
     9	
    10	import (
    11		"unicode"
    12		"unicode/utf8"
    13	)
    14	
    15	// explode splits s into a slice of UTF-8 strings,
    16	// one string per Unicode character up to a maximum of n (n < 0 means no limit).
    17	// Invalid UTF-8 sequences become correct encodings of U+FFFD.
    18	func explode(s string, n int) []string {
    19		l := utf8.RuneCountInString(s)
    20		if n < 0 || n > l {
    21			n = l
    22		}
    23		a := make([]string, n)
    24		for i := 0; i < n-1; i++ {
    25			ch, size := utf8.DecodeRuneInString(s)
    26			a[i] = s[:size]
    27			s = s[size:]
    28			if ch == utf8.RuneError {
    29				a[i] = string(utf8.RuneError)
    30			}
    31		}
    32		if n > 0 {
    33			a[n-1] = s
    34		}
    35		return a
    36	}
    37	
    38	// primeRK is the prime base used in Rabin-Karp algorithm.
    39	const primeRK = 16777619
    40	
    41	// hashStr returns the hash and the appropriate multiplicative
    42	// factor for use in Rabin-Karp algorithm.
    43	func hashStr(sep string) (uint32, uint32) {
    44		hash := uint32(0)
    45		for i := 0; i < len(sep); i++ {
    46			hash = hash*primeRK + uint32(sep[i])
    47		}
    48		var pow, sq uint32 = 1, primeRK
    49		for i := len(sep); i > 0; i >>= 1 {
    50			if i&1 != 0 {
    51				pow *= sq
    52			}
    53			sq *= sq
    54		}
    55		return hash, pow
    56	}
    57	
    58	// hashStrRev returns the hash of the reverse of sep and the
    59	// appropriate multiplicative factor for use in Rabin-Karp algorithm.
    60	func hashStrRev(sep string) (uint32, uint32) {
    61		hash := uint32(0)
    62		for i := len(sep) - 1; i >= 0; i-- {
    63			hash = hash*primeRK + uint32(sep[i])
    64		}
    65		var pow, sq uint32 = 1, primeRK
    66		for i := len(sep); i > 0; i >>= 1 {
    67			if i&1 != 0 {
    68				pow *= sq
    69			}
    70			sq *= sq
    71		}
    72		return hash, pow
    73	}
    74	
    75	// Count counts the number of non-overlapping instances of sep in s.
    76	// If sep is an empty string, Count returns 1 + the number of Unicode code points in s.
    77	func Count(s, sep string) int {
    78		n := 0
    79		// special cases
    80		switch {
    81		case len(sep) == 0:
    82			return utf8.RuneCountInString(s) + 1
    83		case len(sep) == 1:
    84			// special case worth making fast
    85			c := sep[0]
    86			for i := 0; i < len(s); i++ {
    87				if s[i] == c {
    88					n++
    89				}
    90			}
    91			return n
    92		case len(sep) > len(s):
    93			return 0
    94		case len(sep) == len(s):
    95			if sep == s {
    96				return 1
    97			}
    98			return 0
    99		}
   100		// Rabin-Karp search
   101		hashsep, pow := hashStr(sep)
   102		h := uint32(0)
   103		for i := 0; i < len(sep); i++ {
   104			h = h*primeRK + uint32(s[i])
   105		}
   106		lastmatch := 0
   107		if h == hashsep && s[:len(sep)] == sep {
   108			n++
   109			lastmatch = len(sep)
   110		}
   111		for i := len(sep); i < len(s); {
   112			h *= primeRK
   113			h += uint32(s[i])
   114			h -= pow * uint32(s[i-len(sep)])
   115			i++
   116			if h == hashsep && lastmatch <= i-len(sep) && s[i-len(sep):i] == sep {
   117				n++
   118				lastmatch = i
   119			}
   120		}
   121		return n
   122	}
   123	
   124	// Contains reports whether substr is within s.
   125	func Contains(s, substr string) bool {
   126		return Index(s, substr) >= 0
   127	}
   128	
   129	// ContainsAny reports whether any Unicode code points in chars are within s.
   130	func ContainsAny(s, chars string) bool {
   131		return IndexAny(s, chars) >= 0
   132	}
   133	
   134	// ContainsRune reports whether the Unicode code point r is within s.
   135	func ContainsRune(s string, r rune) bool {
   136		return IndexRune(s, r) >= 0
   137	}
   138	
   139	// LastIndex returns the index of the last instance of sep in s, or -1 if sep is not present in s.
   140	func LastIndex(s, sep string) int {
   141		n := len(sep)
   142		switch {
   143		case n == 0:
   144			return len(s)
   145		case n == 1:
   146			return LastIndexByte(s, sep[0])
   147		case n == len(s):
   148			if sep == s {
   149				return 0
   150			}
   151			return -1
   152		case n > len(s):
   153			return -1
   154		}
   155		// Rabin-Karp search from the end of the string
   156		hashsep, pow := hashStrRev(sep)
   157		last := len(s) - n
   158		var h uint32
   159		for i := len(s) - 1; i >= last; i-- {
   160			h = h*primeRK + uint32(s[i])
   161		}
   162		if h == hashsep && s[last:] == sep {
   163			return last
   164		}
   165		for i := last - 1; i >= 0; i-- {
   166			h *= primeRK
   167			h += uint32(s[i])
   168			h -= pow * uint32(s[i+n])
   169			if h == hashsep && s[i:i+n] == sep {
   170				return i
   171			}
   172		}
   173		return -1
   174	}
   175	
   176	// IndexRune returns the index of the first instance of the Unicode code point
   177	// r, or -1 if rune is not present in s.
   178	func IndexRune(s string, r rune) int {
   179		switch {
   180		case r < utf8.RuneSelf:
   181			return IndexByte(s, byte(r))
   182		default:
   183			for i, c := range s {
   184				if c == r {
   185					return i
   186				}
   187			}
   188		}
   189		return -1
   190	}
   191	
   192	// IndexAny returns the index of the first instance of any Unicode code point
   193	// from chars in s, or -1 if no Unicode code point from chars is present in s.
   194	func IndexAny(s, chars string) int {
   195		if len(chars) > 0 {
   196			for i, c := range s {
   197				for _, m := range chars {
   198					if c == m {
   199						return i
   200					}
   201				}
   202			}
   203		}
   204		return -1
   205	}
   206	
   207	// LastIndexAny returns the index of the last instance of any Unicode code
   208	// point from chars in s, or -1 if no Unicode code point from chars is
   209	// present in s.
   210	func LastIndexAny(s, chars string) int {
   211		if len(chars) > 0 {
   212			for i := len(s); i > 0; {
   213				rune, size := utf8.DecodeLastRuneInString(s[0:i])
   214				i -= size
   215				for _, m := range chars {
   216					if rune == m {
   217						return i
   218					}
   219				}
   220			}
   221		}
   222		return -1
   223	}
   224	
   225	// LastIndexByte returns the index of the last instance of c in s, or -1 if c is not present in s.
   226	func LastIndexByte(s string, c byte) int {
   227		for i := len(s) - 1; i >= 0; i-- {
   228			if s[i] == c {
   229				return i
   230			}
   231		}
   232		return -1
   233	}
   234	
   235	// Generic split: splits after each instance of sep,
   236	// including sepSave bytes of sep in the subarrays.
   237	func genSplit(s, sep string, sepSave, n int) []string {
   238		if n == 0 {
   239			return nil
   240		}
   241		if sep == "" {
   242			return explode(s, n)
   243		}
   244		if n < 0 {
   245			n = Count(s, sep) + 1
   246		}
   247		c := sep[0]
   248		start := 0
   249		a := make([]string, n)
   250		na := 0
   251		for i := 0; i+len(sep) <= len(s) && na+1 < n; i++ {
   252			if s[i] == c && (len(sep) == 1 || s[i:i+len(sep)] == sep) {
   253				a[na] = s[start : i+sepSave]
   254				na++
   255				start = i + len(sep)
   256				i += len(sep) - 1
   257			}
   258		}
   259		a[na] = s[start:]
   260		return a[0 : na+1]
   261	}
   262	
   263	// SplitN slices s into substrings separated by sep and returns a slice of
   264	// the substrings between those separators.
   265	// If sep is empty, SplitN splits after each UTF-8 sequence.
   266	// The count determines the number of substrings to return:
   267	//   n > 0: at most n substrings; the last substring will be the unsplit remainder.
   268	//   n == 0: the result is nil (zero substrings)
   269	//   n < 0: all substrings
   270	func SplitN(s, sep string, n int) []string { return genSplit(s, sep, 0, n) }
   271	
   272	// SplitAfterN slices s into substrings after each instance of sep and
   273	// returns a slice of those substrings.
   274	// If sep is empty, SplitAfterN splits after each UTF-8 sequence.
   275	// The count determines the number of substrings to return:
   276	//   n > 0: at most n substrings; the last substring will be the unsplit remainder.
   277	//   n == 0: the result is nil (zero substrings)
   278	//   n < 0: all substrings
   279	func SplitAfterN(s, sep string, n int) []string {
   280		return genSplit(s, sep, len(sep), n)
   281	}
   282	
   283	// Split slices s into all substrings separated by sep and returns a slice of
   284	// the substrings between those separators.
   285	// If sep is empty, Split splits after each UTF-8 sequence.
   286	// It is equivalent to SplitN with a count of -1.
   287	func Split(s, sep string) []string { return genSplit(s, sep, 0, -1) }
   288	
   289	// SplitAfter slices s into all substrings after each instance of sep and
   290	// returns a slice of those substrings.
   291	// If sep is empty, SplitAfter splits after each UTF-8 sequence.
   292	// It is equivalent to SplitAfterN with a count of -1.
   293	func SplitAfter(s, sep string) []string {
   294		return genSplit(s, sep, len(sep), -1)
   295	}
   296	
   297	// Fields splits the string s around each instance of one or more consecutive white space
   298	// characters, as defined by unicode.IsSpace, returning an array of substrings of s or an
   299	// empty list if s contains only white space.
   300	func Fields(s string) []string {
   301		return FieldsFunc(s, unicode.IsSpace)
   302	}
   303	
   304	// FieldsFunc splits the string s at each run of Unicode code points c satisfying f(c)
   305	// and returns an array of slices of s. If all code points in s satisfy f(c) or the
   306	// string is empty, an empty slice is returned.
   307	// FieldsFunc makes no guarantees about the order in which it calls f(c).
   308	// If f does not return consistent results for a given c, FieldsFunc may crash.
   309	func FieldsFunc(s string, f func(rune) bool) []string {
   310		// First count the fields.
   311		n := 0
   312		inField := false
   313		for _, rune := range s {
   314			wasInField := inField
   315			inField = !f(rune)
   316			if inField && !wasInField {
   317				n++
   318			}
   319		}
   320	
   321		// Now create them.
   322		a := make([]string, n)
   323		na := 0
   324		fieldStart := -1 // Set to -1 when looking for start of field.
   325		for i, rune := range s {
   326			if f(rune) {
   327				if fieldStart >= 0 {
   328					a[na] = s[fieldStart:i]
   329					na++
   330					fieldStart = -1
   331				}
   332			} else if fieldStart == -1 {
   333				fieldStart = i
   334			}
   335		}
   336		if fieldStart >= 0 { // Last field might end at EOF.
   337			a[na] = s[fieldStart:]
   338		}
   339		return a
   340	}
   341	
   342	// Join concatenates the elements of a to create a single string. The separator string
   343	// sep is placed between elements in the resulting string.
   344	func Join(a []string, sep string) string {
   345		if len(a) == 0 {
   346			return ""
   347		}
   348		if len(a) == 1 {
   349			return a[0]
   350		}
   351		n := len(sep) * (len(a) - 1)
   352		for i := 0; i < len(a); i++ {
   353			n += len(a[i])
   354		}
   355	
   356		b := make([]byte, n)
   357		bp := copy(b, a[0])
   358		for _, s := range a[1:] {
   359			bp += copy(b[bp:], sep)
   360			bp += copy(b[bp:], s)
   361		}
   362		return string(b)
   363	}
   364	
   365	// HasPrefix tests whether the string s begins with prefix.
   366	func HasPrefix(s, prefix string) bool {
   367		return len(s) >= len(prefix) && s[0:len(prefix)] == prefix
   368	}
   369	
   370	// HasSuffix tests whether the string s ends with suffix.
   371	func HasSuffix(s, suffix string) bool {
   372		return len(s) >= len(suffix) && s[len(s)-len(suffix):] == suffix
   373	}
   374	
   375	// Map returns a copy of the string s with all its characters modified
   376	// according to the mapping function. If mapping returns a negative value, the character is
   377	// dropped from the string with no replacement.
   378	func Map(mapping func(rune) rune, s string) string {
   379		// In the worst case, the string can grow when mapped, making
   380		// things unpleasant. But it's so rare we barge in assuming it's
   381		// fine. It could also shrink but that falls out naturally.
   382		maxbytes := len(s) // length of b
   383		nbytes := 0        // number of bytes encoded in b
   384		// The output buffer b is initialized on demand, the first
   385		// time a character differs.
   386		var b []byte
   387	
   388		for i, c := range s {
   389			r := mapping(c)
   390			if b == nil {
   391				if r == c {
   392					continue
   393				}
   394				b = make([]byte, maxbytes)
   395				nbytes = copy(b, s[:i])
   396			}
   397			if r >= 0 {
   398				wid := 1
   399				if r >= utf8.RuneSelf {
   400					wid = utf8.RuneLen(r)
   401				}
   402				if nbytes+wid > maxbytes {
   403					// Grow the buffer.
   404					maxbytes = maxbytes*2 + utf8.UTFMax
   405					nb := make([]byte, maxbytes)
   406					copy(nb, b[0:nbytes])
   407					b = nb
   408				}
   409				nbytes += utf8.EncodeRune(b[nbytes:maxbytes], r)
   410			}
   411		}
   412		if b == nil {
   413			return s
   414		}
   415		return string(b[0:nbytes])
   416	}
   417	
   418	// Repeat returns a new string consisting of count copies of the string s.
   419	func Repeat(s string, count int) string {
   420		b := make([]byte, len(s)*count)
   421		bp := copy(b, s)
   422		for bp < len(b) {
   423			copy(b[bp:], b[:bp])
   424			bp *= 2
   425		}
   426		return string(b)
   427	}
   428	
   429	// ToUpper returns a copy of the string s with all Unicode letters mapped to their upper case.
   430	func ToUpper(s string) string { return Map(unicode.ToUpper, s) }
   431	
   432	// ToLower returns a copy of the string s with all Unicode letters mapped to their lower case.
   433	func ToLower(s string) string { return Map(unicode.ToLower, s) }
   434	
   435	// ToTitle returns a copy of the string s with all Unicode letters mapped to their title case.
   436	func ToTitle(s string) string { return Map(unicode.ToTitle, s) }
   437	
   438	// ToUpperSpecial returns a copy of the string s with all Unicode letters mapped to their
   439	// upper case, giving priority to the special casing rules.
   440	func ToUpperSpecial(_case unicode.SpecialCase, s string) string {
   441		return Map(func(r rune) rune { return _case.ToUpper(r) }, s)
   442	}
   443	
   444	// ToLowerSpecial returns a copy of the string s with all Unicode letters mapped to their
   445	// lower case, giving priority to the special casing rules.
   446	func ToLowerSpecial(_case unicode.SpecialCase, s string) string {
   447		return Map(func(r rune) rune { return _case.ToLower(r) }, s)
   448	}
   449	
   450	// ToTitleSpecial returns a copy of the string s with all Unicode letters mapped to their
   451	// title case, giving priority to the special casing rules.
   452	func ToTitleSpecial(_case unicode.SpecialCase, s string) string {
   453		return Map(func(r rune) rune { return _case.ToTitle(r) }, s)
   454	}
   455	
   456	// isSeparator reports whether the rune could mark a word boundary.
   457	// TODO: update when package unicode captures more of the properties.
   458	func isSeparator(r rune) bool {
   459		// ASCII alphanumerics and underscore are not separators
   460		if r <= 0x7F {
   461			switch {
   462			case '0' <= r && r <= '9':
   463				return false
   464			case 'a' <= r && r <= 'z':
   465				return false
   466			case 'A' <= r && r <= 'Z':
   467				return false
   468			case r == '_':
   469				return false
   470			}
   471			return true
   472		}
   473		// Letters and digits are not separators
   474		if unicode.IsLetter(r) || unicode.IsDigit(r) {
   475			return false
   476		}
   477		// Otherwise, all we can do for now is treat spaces as separators.
   478		return unicode.IsSpace(r)
   479	}
   480	
   481	// Title returns a copy of the string s with all Unicode letters that begin words
   482	// mapped to their title case.
   483	//
   484	// BUG(rsc): The rule Title uses for word boundaries does not handle Unicode punctuation properly.
   485	func Title(s string) string {
   486		// Use a closure here to remember state.
   487		// Hackish but effective. Depends on Map scanning in order and calling
   488		// the closure once per rune.
   489		prev := ' '
   490		return Map(
   491			func(r rune) rune {
   492				if isSeparator(prev) {
   493					prev = r
   494					return unicode.ToTitle(r)
   495				}
   496				prev = r
   497				return r
   498			},
   499			s)
   500	}
   501	
   502	// TrimLeftFunc returns a slice of the string s with all leading
   503	// Unicode code points c satisfying f(c) removed.
   504	func TrimLeftFunc(s string, f func(rune) bool) string {
   505		i := indexFunc(s, f, false)
   506		if i == -1 {
   507			return ""
   508		}
   509		return s[i:]
   510	}
   511	
   512	// TrimRightFunc returns a slice of the string s with all trailing
   513	// Unicode code points c satisfying f(c) removed.
   514	func TrimRightFunc(s string, f func(rune) bool) string {
   515		i := lastIndexFunc(s, f, false)
   516		if i >= 0 && s[i] >= utf8.RuneSelf {
   517			_, wid := utf8.DecodeRuneInString(s[i:])
   518			i += wid
   519		} else {
   520			i++
   521		}
   522		return s[0:i]
   523	}
   524	
   525	// TrimFunc returns a slice of the string s with all leading
   526	// and trailing Unicode code points c satisfying f(c) removed.
   527	func TrimFunc(s string, f func(rune) bool) string {
   528		return TrimRightFunc(TrimLeftFunc(s, f), f)
   529	}
   530	
   531	// IndexFunc returns the index into s of the first Unicode
   532	// code point satisfying f(c), or -1 if none do.
   533	func IndexFunc(s string, f func(rune) bool) int {
   534		return indexFunc(s, f, true)
   535	}
   536	
   537	// LastIndexFunc returns the index into s of the last
   538	// Unicode code point satisfying f(c), or -1 if none do.
   539	func LastIndexFunc(s string, f func(rune) bool) int {
   540		return lastIndexFunc(s, f, true)
   541	}
   542	
   543	// indexFunc is the same as IndexFunc except that if
   544	// truth==false, the sense of the predicate function is
   545	// inverted.
   546	func indexFunc(s string, f func(rune) bool, truth bool) int {
   547		start := 0
   548		for start < len(s) {
   549			wid := 1
   550			r := rune(s[start])
   551			if r >= utf8.RuneSelf {
   552				r, wid = utf8.DecodeRuneInString(s[start:])
   553			}
   554			if f(r) == truth {
   555				return start
   556			}
   557			start += wid
   558		}
   559		return -1
   560	}
   561	
   562	// lastIndexFunc is the same as LastIndexFunc except that if
   563	// truth==false, the sense of the predicate function is
   564	// inverted.
   565	func lastIndexFunc(s string, f func(rune) bool, truth bool) int {
   566		for i := len(s); i > 0; {
   567			r, size := utf8.DecodeLastRuneInString(s[0:i])
   568			i -= size
   569			if f(r) == truth {
   570				return i
   571			}
   572		}
   573		return -1
   574	}
   575	
   576	func makeCutsetFunc(cutset string) func(rune) bool {
   577		return func(r rune) bool { return IndexRune(cutset, r) >= 0 }
   578	}
   579	
   580	// Trim returns a slice of the string s with all leading and
   581	// trailing Unicode code points contained in cutset removed.
   582	func Trim(s string, cutset string) string {
   583		if s == "" || cutset == "" {
   584			return s
   585		}
   586		return TrimFunc(s, makeCutsetFunc(cutset))
   587	}
   588	
   589	// TrimLeft returns a slice of the string s with all leading
   590	// Unicode code points contained in cutset removed.
   591	func TrimLeft(s string, cutset string) string {
   592		if s == "" || cutset == "" {
   593			return s
   594		}
   595		return TrimLeftFunc(s, makeCutsetFunc(cutset))
   596	}
   597	
   598	// TrimRight returns a slice of the string s, with all trailing
   599	// Unicode code points contained in cutset removed.
   600	func TrimRight(s string, cutset string) string {
   601		if s == "" || cutset == "" {
   602			return s
   603		}
   604		return TrimRightFunc(s, makeCutsetFunc(cutset))
   605	}
   606	
   607	// TrimSpace returns a slice of the string s, with all leading
   608	// and trailing white space removed, as defined by Unicode.
   609	func TrimSpace(s string) string {
   610		return TrimFunc(s, unicode.IsSpace)
   611	}
   612	
   613	// TrimPrefix returns s without the provided leading prefix string.
   614	// If s doesn't start with prefix, s is returned unchanged.
   615	func TrimPrefix(s, prefix string) string {
   616		if HasPrefix(s, prefix) {
   617			return s[len(prefix):]
   618		}
   619		return s
   620	}
   621	
   622	// TrimSuffix returns s without the provided trailing suffix string.
   623	// If s doesn't end with suffix, s is returned unchanged.
   624	func TrimSuffix(s, suffix string) string {
   625		if HasSuffix(s, suffix) {
   626			return s[:len(s)-len(suffix)]
   627		}
   628		return s
   629	}
   630	
   631	// Replace returns a copy of the string s with the first n
   632	// non-overlapping instances of old replaced by new.
   633	// If old is empty, it matches at the beginning of the string
   634	// and after each UTF-8 sequence, yielding up to k+1 replacements
   635	// for a k-rune string.
   636	// If n < 0, there is no limit on the number of replacements.
   637	func Replace(s, old, new string, n int) string {
   638		if old == new || n == 0 {
   639			return s // avoid allocation
   640		}
   641	
   642		// Compute number of replacements.
   643		if m := Count(s, old); m == 0 {
   644			return s // avoid allocation
   645		} else if n < 0 || m < n {
   646			n = m
   647		}
   648	
   649		// Apply replacements to buffer.
   650		t := make([]byte, len(s)+n*(len(new)-len(old)))
   651		w := 0
   652		start := 0
   653		for i := 0; i < n; i++ {
   654			j := start
   655			if len(old) == 0 {
   656				if i > 0 {
   657					_, wid := utf8.DecodeRuneInString(s[start:])
   658					j += wid
   659				}
   660			} else {
   661				j += Index(s[start:], old)
   662			}
   663			w += copy(t[w:], s[start:j])
   664			w += copy(t[w:], new)
   665			start = j + len(old)
   666		}
   667		w += copy(t[w:], s[start:])
   668		return string(t[0:w])
   669	}
   670	
   671	// EqualFold reports whether s and t, interpreted as UTF-8 strings,
   672	// are equal under Unicode case-folding.
   673	func EqualFold(s, t string) bool {
   674		for s != "" && t != "" {
   675			// Extract first rune from each string.
   676			var sr, tr rune
   677			if s[0] < utf8.RuneSelf {
   678				sr, s = rune(s[0]), s[1:]
   679			} else {
   680				r, size := utf8.DecodeRuneInString(s)
   681				sr, s = r, s[size:]
   682			}
   683			if t[0] < utf8.RuneSelf {
   684				tr, t = rune(t[0]), t[1:]
   685			} else {
   686				r, size := utf8.DecodeRuneInString(t)
   687				tr, t = r, t[size:]
   688			}
   689	
   690			// If they match, keep going; if not, return false.
   691	
   692			// Easy case.
   693			if tr == sr {
   694				continue
   695			}
   696	
   697			// Make sr < tr to simplify what follows.
   698			if tr < sr {
   699				tr, sr = sr, tr
   700			}
   701			// Fast check for ASCII.
   702			if tr < utf8.RuneSelf && 'A' <= sr && sr <= 'Z' {
   703				// ASCII, and sr is upper case.  tr must be lower case.
   704				if tr == sr+'a'-'A' {
   705					continue
   706				}
   707				return false
   708			}
   709	
   710			// General case. SimpleFold(x) returns the next equivalent rune > x
   711			// or wraps around to smaller values.
   712			r := unicode.SimpleFold(sr)
   713			for r != sr && r < tr {
   714				r = unicode.SimpleFold(r)
   715			}
   716			if r == tr {
   717				continue
   718			}
   719			return false
   720		}
   721	
   722		// One string is empty. Are both?
   723		return s == t
   724	}
   725	

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