Source file src/pkg/bytes/bytes.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 bytes implements functions for the manipulation of byte slices.
     6	// It is analogous to the facilities of the strings package.
     7	package bytes
     8	
     9	import (
    10		"unicode"
    11		"unicode/utf8"
    12	)
    13	
    14	// Compare returns an integer comparing two byte slices lexicographically.
    15	// The result will be 0 if a==b, -1 if a < b, and +1 if a > b.
    16	// A nil argument is equivalent to an empty slice.
    17	func Compare(a, b []byte) int {
    18		m := len(a)
    19		if m > len(b) {
    20			m = len(b)
    21		}
    22		for i, ac := range a[0:m] {
    23			bc := b[i]
    24			switch {
    25			case ac > bc:
    26				return 1
    27			case ac < bc:
    28				return -1
    29			}
    30		}
    31		switch {
    32		case len(a) < len(b):
    33			return -1
    34		case len(a) > len(b):
    35			return 1
    36		}
    37		return 0
    38	}
    39	
    40	func equalPortable(a, b []byte) bool {
    41		if len(a) != len(b) {
    42			return false
    43		}
    44		for i, c := range a {
    45			if c != b[i] {
    46				return false
    47			}
    48		}
    49		return true
    50	}
    51	
    52	// explode splits s into a slice of UTF-8 sequences, one per Unicode character (still slices of bytes),
    53	// up to a maximum of n byte slices. Invalid UTF-8 sequences are chopped into individual bytes.
    54	func explode(s []byte, n int) [][]byte {
    55		if n <= 0 {
    56			n = len(s)
    57		}
    58		a := make([][]byte, n)
    59		var size int
    60		na := 0
    61		for len(s) > 0 {
    62			if na+1 >= n {
    63				a[na] = s
    64				na++
    65				break
    66			}
    67			_, size = utf8.DecodeRune(s)
    68			a[na] = s[0:size]
    69			s = s[size:]
    70			na++
    71		}
    72		return a[0:na]
    73	}
    74	
    75	// Count counts the number of non-overlapping instances of sep in s.
    76	func Count(s, sep []byte) int {
    77		n := len(sep)
    78		if n == 0 {
    79			return utf8.RuneCount(s) + 1
    80		}
    81		if n > len(s) {
    82			return 0
    83		}
    84		count := 0
    85		c := sep[0]
    86		i := 0
    87		t := s[:len(s)-n+1]
    88		for i < len(t) {
    89			if t[i] != c {
    90				o := IndexByte(t[i:], c)
    91				if o < 0 {
    92					break
    93				}
    94				i += o
    95			}
    96			if n == 1 || Equal(s[i:i+n], sep) {
    97				count++
    98				i += n
    99				continue
   100			}
   101			i++
   102		}
   103		return count
   104	}
   105	
   106	// Contains returns whether subslice is within b.
   107	func Contains(b, subslice []byte) bool {
   108		return Index(b, subslice) != -1
   109	}
   110	
   111	// Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
   112	func Index(s, sep []byte) int {
   113		n := len(sep)
   114		if n == 0 {
   115			return 0
   116		}
   117		if n > len(s) {
   118			return -1
   119		}
   120		c := sep[0]
   121		if n == 1 {
   122			return IndexByte(s, c)
   123		}
   124		i := 0
   125		t := s[:len(s)-n+1]
   126		for i < len(t) {
   127			if t[i] != c {
   128				o := IndexByte(t[i:], c)
   129				if o < 0 {
   130					break
   131				}
   132				i += o
   133			}
   134			if Equal(s[i:i+n], sep) {
   135				return i
   136			}
   137			i++
   138		}
   139		return -1
   140	}
   141	
   142	func indexBytePortable(s []byte, c byte) int {
   143		for i, b := range s {
   144			if b == c {
   145				return i
   146			}
   147		}
   148		return -1
   149	}
   150	
   151	// LastIndex returns the index of the last instance of sep in s, or -1 if sep is not present in s.
   152	func LastIndex(s, sep []byte) int {
   153		n := len(sep)
   154		if n == 0 {
   155			return len(s)
   156		}
   157		c := sep[0]
   158		for i := len(s) - n; i >= 0; i-- {
   159			if s[i] == c && (n == 1 || Equal(s[i:i+n], sep)) {
   160				return i
   161			}
   162		}
   163		return -1
   164	}
   165	
   166	// IndexRune interprets s as a sequence of UTF-8-encoded Unicode code points.
   167	// It returns the byte index of the first occurrence in s of the given rune.
   168	// It returns -1 if rune is not present in s.
   169	func IndexRune(s []byte, r rune) int {
   170		for i := 0; i < len(s); {
   171			r1, size := utf8.DecodeRune(s[i:])
   172			if r == r1 {
   173				return i
   174			}
   175			i += size
   176		}
   177		return -1
   178	}
   179	
   180	// IndexAny interprets s as a sequence of UTF-8-encoded Unicode code points.
   181	// It returns the byte index of the first occurrence in s of any of the Unicode
   182	// code points in chars.  It returns -1 if chars is empty or if there is no code
   183	// point in common.
   184	func IndexAny(s []byte, chars string) int {
   185		if len(chars) > 0 {
   186			var r rune
   187			var width int
   188			for i := 0; i < len(s); i += width {
   189				r = rune(s[i])
   190				if r < utf8.RuneSelf {
   191					width = 1
   192				} else {
   193					r, width = utf8.DecodeRune(s[i:])
   194				}
   195				for _, ch := range chars {
   196					if r == ch {
   197						return i
   198					}
   199				}
   200			}
   201		}
   202		return -1
   203	}
   204	
   205	// LastIndexAny interprets s as a sequence of UTF-8-encoded Unicode code
   206	// points.  It returns the byte index of the last occurrence in s of any of
   207	// the Unicode code points in chars.  It returns -1 if chars is empty or if
   208	// there is no code point in common.
   209	func LastIndexAny(s []byte, chars string) int {
   210		if len(chars) > 0 {
   211			for i := len(s); i > 0; {
   212				r, size := utf8.DecodeLastRune(s[0:i])
   213				i -= size
   214				for _, ch := range chars {
   215					if r == ch {
   216						return i
   217					}
   218				}
   219			}
   220		}
   221		return -1
   222	}
   223	
   224	// Generic split: splits after each instance of sep,
   225	// including sepSave bytes of sep in the subslices.
   226	func genSplit(s, sep []byte, sepSave, n int) [][]byte {
   227		if n == 0 {
   228			return nil
   229		}
   230		if len(sep) == 0 {
   231			return explode(s, n)
   232		}
   233		if n < 0 {
   234			n = Count(s, sep) + 1
   235		}
   236		c := sep[0]
   237		start := 0
   238		a := make([][]byte, n)
   239		na := 0
   240		for i := 0; i+len(sep) <= len(s) && na+1 < n; i++ {
   241			if s[i] == c && (len(sep) == 1 || Equal(s[i:i+len(sep)], sep)) {
   242				a[na] = s[start : i+sepSave]
   243				na++
   244				start = i + len(sep)
   245				i += len(sep) - 1
   246			}
   247		}
   248		a[na] = s[start:]
   249		return a[0 : na+1]
   250	}
   251	
   252	// SplitN slices s into subslices separated by sep and returns a slice of
   253	// the subslices between those separators.
   254	// If sep is empty, SplitN splits after each UTF-8 sequence.
   255	// The count determines the number of subslices to return:
   256	//   n > 0: at most n subslices; the last subslice will be the unsplit remainder.
   257	//   n == 0: the result is nil (zero subslices)
   258	//   n < 0: all subslices
   259	func SplitN(s, sep []byte, n int) [][]byte { return genSplit(s, sep, 0, n) }
   260	
   261	// SplitAfterN slices s into subslices after each instance of sep and
   262	// returns a slice of those subslices.
   263	// If sep is empty, SplitAfterN splits after each UTF-8 sequence.
   264	// The count determines the number of subslices to return:
   265	//   n > 0: at most n subslices; the last subslice will be the unsplit remainder.
   266	//   n == 0: the result is nil (zero subslices)
   267	//   n < 0: all subslices
   268	func SplitAfterN(s, sep []byte, n int) [][]byte {
   269		return genSplit(s, sep, len(sep), n)
   270	}
   271	
   272	// Split slices s into all subslices separated by sep and returns a slice of
   273	// the subslices between those separators.
   274	// If sep is empty, Split splits after each UTF-8 sequence.
   275	// It is equivalent to SplitN with a count of -1.
   276	func Split(s, sep []byte) [][]byte { return genSplit(s, sep, 0, -1) }
   277	
   278	// SplitAfter slices s into all subslices after each instance of sep and
   279	// returns a slice of those subslices.
   280	// If sep is empty, SplitAfter splits after each UTF-8 sequence.
   281	// It is equivalent to SplitAfterN with a count of -1.
   282	func SplitAfter(s, sep []byte) [][]byte {
   283		return genSplit(s, sep, len(sep), -1)
   284	}
   285	
   286	// Fields splits the slice s around each instance of one or more consecutive white space
   287	// characters, returning a slice of subslices of s or an empty list if s contains only white space.
   288	func Fields(s []byte) [][]byte {
   289		return FieldsFunc(s, unicode.IsSpace)
   290	}
   291	
   292	// FieldsFunc interprets s as a sequence of UTF-8-encoded Unicode code points.
   293	// It splits the slice s at each run of code points c satisfying f(c) and
   294	// returns a slice of subslices of s.  If no code points in s satisfy f(c), an
   295	// empty slice is returned.
   296	func FieldsFunc(s []byte, f func(rune) bool) [][]byte {
   297		n := 0
   298		inField := false
   299		for i := 0; i < len(s); {
   300			r, size := utf8.DecodeRune(s[i:])
   301			wasInField := inField
   302			inField = !f(r)
   303			if inField && !wasInField {
   304				n++
   305			}
   306			i += size
   307		}
   308	
   309		a := make([][]byte, n)
   310		na := 0
   311		fieldStart := -1
   312		for i := 0; i <= len(s) && na < n; {
   313			r, size := utf8.DecodeRune(s[i:])
   314			if fieldStart < 0 && size > 0 && !f(r) {
   315				fieldStart = i
   316				i += size
   317				continue
   318			}
   319			if fieldStart >= 0 && (size == 0 || f(r)) {
   320				a[na] = s[fieldStart:i]
   321				na++
   322				fieldStart = -1
   323			}
   324			if size == 0 {
   325				break
   326			}
   327			i += size
   328		}
   329		return a[0:na]
   330	}
   331	
   332	// Join concatenates the elements of s to create a new byte slice. The separator
   333	// sep is placed between elements in the resulting slice.
   334	func Join(s [][]byte, sep []byte) []byte {
   335		if len(s) == 0 {
   336			return []byte{}
   337		}
   338		if len(s) == 1 {
   339			// Just return a copy.
   340			return append([]byte(nil), s[0]...)
   341		}
   342		n := len(sep) * (len(s) - 1)
   343		for _, v := range s {
   344			n += len(v)
   345		}
   346	
   347		b := make([]byte, n)
   348		bp := copy(b, s[0])
   349		for _, v := range s[1:] {
   350			bp += copy(b[bp:], sep)
   351			bp += copy(b[bp:], v)
   352		}
   353		return b
   354	}
   355	
   356	// HasPrefix tests whether the byte slice s begins with prefix.
   357	func HasPrefix(s, prefix []byte) bool {
   358		return len(s) >= len(prefix) && Equal(s[0:len(prefix)], prefix)
   359	}
   360	
   361	// HasSuffix tests whether the byte slice s ends with suffix.
   362	func HasSuffix(s, suffix []byte) bool {
   363		return len(s) >= len(suffix) && Equal(s[len(s)-len(suffix):], suffix)
   364	}
   365	
   366	// Map returns a copy of the byte slice s with all its characters modified
   367	// according to the mapping function. If mapping returns a negative value, the character is
   368	// dropped from the string with no replacement.  The characters in s and the
   369	// output are interpreted as UTF-8-encoded Unicode code points.
   370	func Map(mapping func(r rune) rune, s []byte) []byte {
   371		// In the worst case, the slice can grow when mapped, making
   372		// things unpleasant.  But it's so rare we barge in assuming it's
   373		// fine.  It could also shrink but that falls out naturally.
   374		maxbytes := len(s) // length of b
   375		nbytes := 0        // number of bytes encoded in b
   376		b := make([]byte, maxbytes)
   377		for i := 0; i < len(s); {
   378			wid := 1
   379			r := rune(s[i])
   380			if r >= utf8.RuneSelf {
   381				r, wid = utf8.DecodeRune(s[i:])
   382			}
   383			r = mapping(r)
   384			if r >= 0 {
   385				if nbytes+utf8.RuneLen(r) > maxbytes {
   386					// Grow the buffer.
   387					maxbytes = maxbytes*2 + utf8.UTFMax
   388					nb := make([]byte, maxbytes)
   389					copy(nb, b[0:nbytes])
   390					b = nb
   391				}
   392				nbytes += utf8.EncodeRune(b[nbytes:maxbytes], r)
   393			}
   394			i += wid
   395		}
   396		return b[0:nbytes]
   397	}
   398	
   399	// Repeat returns a new byte slice consisting of count copies of b.
   400	func Repeat(b []byte, count int) []byte {
   401		nb := make([]byte, len(b)*count)
   402		bp := 0
   403		for i := 0; i < count; i++ {
   404			for j := 0; j < len(b); j++ {
   405				nb[bp] = b[j]
   406				bp++
   407			}
   408		}
   409		return nb
   410	}
   411	
   412	// ToUpper returns a copy of the byte slice s with all Unicode letters mapped to their upper case.
   413	func ToUpper(s []byte) []byte { return Map(unicode.ToUpper, s) }
   414	
   415	// ToLower returns a copy of the byte slice s with all Unicode letters mapped to their lower case.
   416	func ToLower(s []byte) []byte { return Map(unicode.ToLower, s) }
   417	
   418	// ToTitle returns a copy of the byte slice s with all Unicode letters mapped to their title case.
   419	func ToTitle(s []byte) []byte { return Map(unicode.ToTitle, s) }
   420	
   421	// ToUpperSpecial returns a copy of the byte slice s with all Unicode letters mapped to their
   422	// upper case, giving priority to the special casing rules.
   423	func ToUpperSpecial(_case unicode.SpecialCase, s []byte) []byte {
   424		return Map(func(r rune) rune { return _case.ToUpper(r) }, s)
   425	}
   426	
   427	// ToLowerSpecial returns a copy of the byte slice s with all Unicode letters mapped to their
   428	// lower case, giving priority to the special casing rules.
   429	func ToLowerSpecial(_case unicode.SpecialCase, s []byte) []byte {
   430		return Map(func(r rune) rune { return _case.ToLower(r) }, s)
   431	}
   432	
   433	// ToTitleSpecial returns a copy of the byte slice s with all Unicode letters mapped to their
   434	// title case, giving priority to the special casing rules.
   435	func ToTitleSpecial(_case unicode.SpecialCase, s []byte) []byte {
   436		return Map(func(r rune) rune { return _case.ToTitle(r) }, s)
   437	}
   438	
   439	// isSeparator reports whether the rune could mark a word boundary.
   440	// TODO: update when package unicode captures more of the properties.
   441	func isSeparator(r rune) bool {
   442		// ASCII alphanumerics and underscore are not separators
   443		if r <= 0x7F {
   444			switch {
   445			case '0' <= r && r <= '9':
   446				return false
   447			case 'a' <= r && r <= 'z':
   448				return false
   449			case 'A' <= r && r <= 'Z':
   450				return false
   451			case r == '_':
   452				return false
   453			}
   454			return true
   455		}
   456		// Letters and digits are not separators
   457		if unicode.IsLetter(r) || unicode.IsDigit(r) {
   458			return false
   459		}
   460		// Otherwise, all we can do for now is treat spaces as separators.
   461		return unicode.IsSpace(r)
   462	}
   463	
   464	// Title returns a copy of s with all Unicode letters that begin words
   465	// mapped to their title case.
   466	//
   467	// BUG: The rule Title uses for word boundaries does not handle Unicode punctuation properly.
   468	func Title(s []byte) []byte {
   469		// Use a closure here to remember state.
   470		// Hackish but effective. Depends on Map scanning in order and calling
   471		// the closure once per rune.
   472		prev := ' '
   473		return Map(
   474			func(r rune) rune {
   475				if isSeparator(prev) {
   476					prev = r
   477					return unicode.ToTitle(r)
   478				}
   479				prev = r
   480				return r
   481			},
   482			s)
   483	}
   484	
   485	// TrimLeftFunc returns a subslice of s by slicing off all leading UTF-8-encoded
   486	// Unicode code points c that satisfy f(c).
   487	func TrimLeftFunc(s []byte, f func(r rune) bool) []byte {
   488		i := indexFunc(s, f, false)
   489		if i == -1 {
   490			return nil
   491		}
   492		return s[i:]
   493	}
   494	
   495	// TrimRightFunc returns a subslice of s by slicing off all trailing UTF-8
   496	// encoded Unicode code points c that satisfy f(c).
   497	func TrimRightFunc(s []byte, f func(r rune) bool) []byte {
   498		i := lastIndexFunc(s, f, false)
   499		if i >= 0 && s[i] >= utf8.RuneSelf {
   500			_, wid := utf8.DecodeRune(s[i:])
   501			i += wid
   502		} else {
   503			i++
   504		}
   505		return s[0:i]
   506	}
   507	
   508	// TrimFunc returns a subslice of s by slicing off all leading and trailing
   509	// UTF-8-encoded Unicode code points c that satisfy f(c).
   510	func TrimFunc(s []byte, f func(r rune) bool) []byte {
   511		return TrimRightFunc(TrimLeftFunc(s, f), f)
   512	}
   513	
   514	// TrimPrefix returns s without the provided leading prefix string.
   515	// If s doesn't start with prefix, s is returned unchanged.
   516	func TrimPrefix(s, prefix []byte) []byte {
   517		if HasPrefix(s, prefix) {
   518			return s[len(prefix):]
   519		}
   520		return s
   521	}
   522	
   523	// TrimSuffix returns s without the provided trailing suffix string.
   524	// If s doesn't end with suffix, s is returned unchanged.
   525	func TrimSuffix(s, suffix []byte) []byte {
   526		if HasSuffix(s, suffix) {
   527			return s[:len(s)-len(suffix)]
   528		}
   529		return s
   530	}
   531	
   532	// IndexFunc interprets s as a sequence of UTF-8-encoded Unicode code points.
   533	// It returns the byte index in s of the first Unicode
   534	// code point satisfying f(c), or -1 if none do.
   535	func IndexFunc(s []byte, f func(r rune) bool) int {
   536		return indexFunc(s, f, true)
   537	}
   538	
   539	// LastIndexFunc interprets s as a sequence of UTF-8-encoded Unicode code points.
   540	// It returns the byte index in s of the last Unicode
   541	// code point satisfying f(c), or -1 if none do.
   542	func LastIndexFunc(s []byte, f func(r rune) bool) int {
   543		return lastIndexFunc(s, f, true)
   544	}
   545	
   546	// indexFunc is the same as IndexFunc except that if
   547	// truth==false, the sense of the predicate function is
   548	// inverted.
   549	func indexFunc(s []byte, f func(r rune) bool, truth bool) int {
   550		start := 0
   551		for start < len(s) {
   552			wid := 1
   553			r := rune(s[start])
   554			if r >= utf8.RuneSelf {
   555				r, wid = utf8.DecodeRune(s[start:])
   556			}
   557			if f(r) == truth {
   558				return start
   559			}
   560			start += wid
   561		}
   562		return -1
   563	}
   564	
   565	// lastIndexFunc is the same as LastIndexFunc except that if
   566	// truth==false, the sense of the predicate function is
   567	// inverted.
   568	func lastIndexFunc(s []byte, f func(r rune) bool, truth bool) int {
   569		for i := len(s); i > 0; {
   570			r, size := rune(s[i-1]), 1
   571			if r >= utf8.RuneSelf {
   572				r, size = utf8.DecodeLastRune(s[0:i])
   573			}
   574			i -= size
   575			if f(r) == truth {
   576				return i
   577			}
   578		}
   579		return -1
   580	}
   581	
   582	func makeCutsetFunc(cutset string) func(r rune) bool {
   583		return func(r rune) bool {
   584			for _, c := range cutset {
   585				if c == r {
   586					return true
   587				}
   588			}
   589			return false
   590		}
   591	}
   592	
   593	// Trim returns a subslice of s by slicing off all leading and
   594	// trailing UTF-8-encoded Unicode code points contained in cutset.
   595	func Trim(s []byte, cutset string) []byte {
   596		return TrimFunc(s, makeCutsetFunc(cutset))
   597	}
   598	
   599	// TrimLeft returns a subslice of s by slicing off all leading
   600	// UTF-8-encoded Unicode code points contained in cutset.
   601	func TrimLeft(s []byte, cutset string) []byte {
   602		return TrimLeftFunc(s, makeCutsetFunc(cutset))
   603	}
   604	
   605	// TrimRight returns a subslice of s by slicing off all trailing
   606	// UTF-8-encoded Unicode code points that are contained in cutset.
   607	func TrimRight(s []byte, cutset string) []byte {
   608		return TrimRightFunc(s, makeCutsetFunc(cutset))
   609	}
   610	
   611	// TrimSpace returns a subslice of s by slicing off all leading and
   612	// trailing white space, as defined by Unicode.
   613	func TrimSpace(s []byte) []byte {
   614		return TrimFunc(s, unicode.IsSpace)
   615	}
   616	
   617	// Runes returns a slice of runes (Unicode code points) equivalent to s.
   618	func Runes(s []byte) []rune {
   619		t := make([]rune, utf8.RuneCount(s))
   620		i := 0
   621		for len(s) > 0 {
   622			r, l := utf8.DecodeRune(s)
   623			t[i] = r
   624			i++
   625			s = s[l:]
   626		}
   627		return t
   628	}
   629	
   630	// Replace returns a copy of the slice s with the first n
   631	// non-overlapping instances of old replaced by new.
   632	// If n < 0, there is no limit on the number of replacements.
   633	func Replace(s, old, new []byte, n int) []byte {
   634		m := 0
   635		if n != 0 {
   636			// Compute number of replacements.
   637			m = Count(s, old)
   638		}
   639		if m == 0 {
   640			// Just return a copy.
   641			return append([]byte(nil), s...)
   642		}
   643		if n < 0 || m < n {
   644			n = m
   645		}
   646	
   647		// Apply replacements to buffer.
   648		t := make([]byte, len(s)+n*(len(new)-len(old)))
   649		w := 0
   650		start := 0
   651		for i := 0; i < n; i++ {
   652			j := start
   653			if len(old) == 0 {
   654				if i > 0 {
   655					_, wid := utf8.DecodeRune(s[start:])
   656					j += wid
   657				}
   658			} else {
   659				j += Index(s[start:], old)
   660			}
   661			w += copy(t[w:], s[start:j])
   662			w += copy(t[w:], new)
   663			start = j + len(old)
   664		}
   665		w += copy(t[w:], s[start:])
   666		return t[0:w]
   667	}
   668	
   669	// EqualFold reports whether s and t, interpreted as UTF-8 strings,
   670	// are equal under Unicode case-folding.
   671	func EqualFold(s, t []byte) bool {
   672		for len(s) != 0 && len(t) != 0 {
   673			// Extract first rune from each.
   674			var sr, tr rune
   675			if s[0] < utf8.RuneSelf {
   676				sr, s = rune(s[0]), s[1:]
   677			} else {
   678				r, size := utf8.DecodeRune(s)
   679				sr, s = r, s[size:]
   680			}
   681			if t[0] < utf8.RuneSelf {
   682				tr, t = rune(t[0]), t[1:]
   683			} else {
   684				r, size := utf8.DecodeRune(t)
   685				tr, t = r, t[size:]
   686			}
   687	
   688			// If they match, keep going; if not, return false.
   689	
   690			// Easy case.
   691			if tr == sr {
   692				continue
   693			}
   694	
   695			// Make sr < tr to simplify what follows.
   696			if tr < sr {
   697				tr, sr = sr, tr
   698			}
   699			// Fast check for ASCII.
   700			if tr < utf8.RuneSelf && 'A' <= sr && sr <= 'Z' {
   701				// ASCII, and sr is upper case.  tr must be lower case.
   702				if tr == sr+'a'-'A' {
   703					continue
   704				}
   705				return false
   706			}
   707	
   708			// General case.  SimpleFold(x) returns the next equivalent rune > x
   709			// or wraps around to smaller values.
   710			r := unicode.SimpleFold(sr)
   711			for r != sr && r < tr {
   712				r = unicode.SimpleFold(r)
   713			}
   714			if r == tr {
   715				continue
   716			}
   717			return false
   718		}
   719	
   720		// One string is empty.  Are both?
   721		return len(s) == len(t)
   722	}

View as plain text