src/bytes/bytes.go - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // Package bytes implements functions for the manipulation of byte slices.
 // It is analogous to the facilities of the strings package.
 package bytes

 import (
 	"unicode"
 	"unicode/utf8"
 )

 func equalPortable(a, b []byte) bool {
 	if len(a) != len(b) {
 		return false
 	}
 	for i, c := range a {
 		if c != b[i] {
 			return false
 		}
 	}
 	return true
 }

 // explode splits s into a slice of UTF-8 sequences, one per Unicode code point (still slices of bytes),
 // up to a maximum of n byte slices. Invalid UTF-8 sequences are chopped into individual bytes.
 func explode(s []byte, n int) [][]byte {
 	if n <= 0 {
 		n = len(s)
 	}
 	a := make([][]byte, n)
 	var size int
 	na := 0
 	for len(s) > 0 {
 		if na+1 >= n {
 			a[na] = s
 			na++
 			break
 		}
 		_, size = utf8.DecodeRune(s)
 		a[na] = s[0:size]
 		s = s[size:]
 		na++
 	}
 	return a[0:na]
 }

 // Count counts the number of non-overlapping instances of sep in s.
 // If sep is an empty slice, Count returns 1 + the number of Unicode code points in s.
 func Count(s, sep []byte) int {
 	n := len(sep)
 	if n == 0 {
 		return utf8.RuneCount(s) + 1
 	}
 	if n > len(s) {
 		return 0
 	}
 	count := 0
 	c := sep[0]
 	i := 0
 	t := s[:len(s)-n+1]
 	for i < len(t) {
 		if t[i] != c {
 			o := IndexByte(t[i:], c)
 			if o < 0 {
 				break
 			}
 			i += o
 		}
 		if n == 1 || Equal(s[i:i+n], sep) {
 			count++
 			i += n
 			continue
 		}
 		i++
 	}
 	return count
 }

 // Contains reports whether subslice is within b.
 func Contains(b, subslice []byte) bool {
 	return Index(b, subslice) != -1
 }

 // Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
 func Index(s, sep []byte) int {
 	n := len(sep)
 	if n == 0 {
 		return 0
 	}
 	if n > len(s) {
 		return -1
 	}
 	c := sep[0]
 	if n == 1 {
 		return IndexByte(s, c)
 	}
 	i := 0
 	t := s[:len(s)-n+1]
 	for i < len(t) {
 		if t[i] != c {
 			o := IndexByte(t[i:], c)
 			if o < 0 {
 				break
 			}
 			i += o
 		}
 		if Equal(s[i:i+n], sep) {
 			return i
 		}
 		i++
 	}
 	return -1
 }

 func indexBytePortable(s []byte, c byte) int {
 	for i, b := range s {
 		if b == c {
 			return i
 		}
 	}
 	return -1
 }

 // LastIndex returns the index of the last instance of sep in s, or -1 if sep is not present in s.
 func LastIndex(s, sep []byte) int {
 	n := len(sep)
 	if n == 0 {
 		return len(s)
 	}
 	c := sep[0]
 	for i := len(s) - n; i >= 0; i-- {
 		if s[i] == c && (n == 1 || Equal(s[i:i+n], sep)) {
 			return i
 		}
 	}
 	return -1
 }

 // LastIndexByte returns the index of the last instance of c in s, or -1 if c is not present in s.
 func LastIndexByte(s []byte, c byte) int {
 	for i := len(s) - 1; i >= 0; i-- {
 		if s[i] == c {
 			return i
 		}
 	}
 	return -1
 }

 // IndexRune interprets s as a sequence of UTF-8-encoded Unicode code points.
 // It returns the byte index of the first occurrence in s of the given rune.
 // It returns -1 if rune is not present in s.
 func IndexRune(s []byte, r rune) int {
 	for i := 0; i < len(s); {
 		r1, size := utf8.DecodeRune(s[i:])
 		if r == r1 {
 			return i
 		}
 		i += size
 	}
 	return -1
 }

 // IndexAny interprets s as a sequence of UTF-8-encoded Unicode code points.
 // It returns the byte index of the first occurrence in s of any of the Unicode
 // code points in chars.  It returns -1 if chars is empty or if there is no code
 // point in common.
 func IndexAny(s []byte, chars string) int {
 	if len(chars) > 0 {
 		var r rune
 		var width int
 		for i := 0; i < len(s); i += width {
 			r = rune(s[i])
 			if r < utf8.RuneSelf {
 				width = 1
 			} else {
 				r, width = utf8.DecodeRune(s[i:])
 			}
 			for _, ch := range chars {
 				if r == ch {
 					return i
 				}
 			}
 		}
 	}
 	return -1
 }

 // LastIndexAny interprets s as a sequence of UTF-8-encoded Unicode code
 // points.  It returns the byte index of the last occurrence in s of any of
 // the Unicode code points in chars.  It returns -1 if chars is empty or if
 // there is no code point in common.
 func LastIndexAny(s []byte, chars string) int {
 	if len(chars) > 0 {
 		for i := len(s); i > 0; {
 			r, size := utf8.DecodeLastRune(s[0:i])
 			i -= size
 			for _, ch := range chars {
 				if r == ch {
 					return i
 				}
 			}
 		}
 	}
 	return -1
 }

 // Generic split: splits after each instance of sep,
 // including sepSave bytes of sep in the subslices.
 func genSplit(s, sep []byte, sepSave, n int) [][]byte {
 	if n == 0 {
 		return nil
 	}
 	if len(sep) == 0 {
 		return explode(s, n)
 	}
 	if n < 0 {
 		n = Count(s, sep) + 1
 	}
 	c := sep[0]
 	start := 0
 	a := make([][]byte, n)
 	na := 0
 	for i := 0; i+len(sep) <= len(s) && na+1 < n; i++ {
 		if s[i] == c && (len(sep) == 1 || Equal(s[i:i+len(sep)], sep)) {
 			a[na] = s[start : i+sepSave]
 			na++
 			start = i + len(sep)
 			i += len(sep) - 1
 		}
 	}
 	a[na] = s[start:]
 	return a[0 : na+1]
 }

 // SplitN slices s into subslices separated by sep and returns a slice of
 // the subslices between those separators.
 // If sep is empty, SplitN splits after each UTF-8 sequence.
 // The count determines the number of subslices to return:
 //   n > 0: at most n subslices; the last subslice will be the unsplit remainder.
 //   n == 0: the result is nil (zero subslices)
 //   n < 0: all subslices
 func SplitN(s, sep []byte, n int) [][]byte { return genSplit(s, sep, 0, n) }

 // SplitAfterN slices s into subslices after each instance of sep and
 // returns a slice of those subslices.
 // If sep is empty, SplitAfterN splits after each UTF-8 sequence.
 // The count determines the number of subslices to return:
 //   n > 0: at most n subslices; the last subslice will be the unsplit remainder.
 //   n == 0: the result is nil (zero subslices)
 //   n < 0: all subslices
 func SplitAfterN(s, sep []byte, n int) [][]byte {
 	return genSplit(s, sep, len(sep), n)
 }

 // Split slices s into all subslices separated by sep and returns a slice of
 // the subslices between those separators.
 // If sep is empty, Split splits after each UTF-8 sequence.
 // It is equivalent to SplitN with a count of -1.
 func Split(s, sep []byte) [][]byte { return genSplit(s, sep, 0, -1) }

 // SplitAfter slices s into all subslices after each instance of sep and
 // returns a slice of those subslices.
 // If sep is empty, SplitAfter splits after each UTF-8 sequence.
 // It is equivalent to SplitAfterN with a count of -1.
 func SplitAfter(s, sep []byte) [][]byte {
 	return genSplit(s, sep, len(sep), -1)
 }

 // Fields splits the slice s around each instance of one or more consecutive white space
 // characters, returning a slice of subslices of s or an empty list if s contains only white space.
 func Fields(s []byte) [][]byte {
 	return FieldsFunc(s, unicode.IsSpace)
 }

 // FieldsFunc interprets s as a sequence of UTF-8-encoded Unicode code points.
 // It splits the slice s at each run of code points c satisfying f(c) and
 // returns a slice of subslices of s.  If all code points in s satisfy f(c), or
 // len(s) == 0, an empty slice is returned.
 // FieldsFunc makes no guarantees about the order in which it calls f(c).
 // If f does not return consistent results for a given c, FieldsFunc may crash.
 func FieldsFunc(s []byte, f func(rune) bool) [][]byte {
 	n := 0
 	inField := false
 	for i := 0; i < len(s); {
 		r, size := utf8.DecodeRune(s[i:])
 		wasInField := inField
 		inField = !f(r)
 		if inField && !wasInField {
 			n++
 		}
 		i += size
 	}

 	a := make([][]byte, n)
 	na := 0
 	fieldStart := -1
 	for i := 0; i <= len(s) && na < n; {
 		r, size := utf8.DecodeRune(s[i:])
 		if fieldStart < 0 && size > 0 && !f(r) {
 			fieldStart = i
 			i += size
 			continue
 		}
 		if fieldStart >= 0 && (size == 0 || f(r)) {
 			a[na] = s[fieldStart:i]
 			na++
 			fieldStart = -1
 		}
 		if size == 0 {
 			break
 		}
 		i += size
 	}
 	return a[0:na]
 }

 // Join concatenates the elements of s to create a new byte slice. The separator
 // sep is placed between elements in the resulting slice.
 func Join(s [][]byte, sep []byte) []byte {
 	if len(s) == 0 {
 		return []byte{}
 	}
 	if len(s) == 1 {
 		// Just return a copy.
 		return append([]byte(nil), s[0]...)
 	}
 	n := len(sep) * (len(s) - 1)
 	for _, v := range s {
 		n += len(v)
 	}

 	b := make([]byte, n)
 	bp := copy(b, s[0])
 	for _, v := range s[1:] {
 		bp += copy(b[bp:], sep)
 		bp += copy(b[bp:], v)
 	}
 	return b
 }

 // HasPrefix tests whether the byte slice s begins with prefix.
 func HasPrefix(s, prefix []byte) bool {
 	return len(s) >= len(prefix) && Equal(s[0:len(prefix)], prefix)
 }

 // HasSuffix tests whether the byte slice s ends with suffix.
 func HasSuffix(s, suffix []byte) bool {
 	return len(s) >= len(suffix) && Equal(s[len(s)-len(suffix):], suffix)
 }

 // Map returns a copy of the byte slice s with all its characters modified
 // according to the mapping function. If mapping returns a negative value, the character is
 // dropped from the string with no replacement.  The characters in s and the
 // output are interpreted as UTF-8-encoded Unicode code points.
 func Map(mapping func(r rune) rune, s []byte) []byte {
 	// In the worst case, the slice can grow when mapped, making
 	// things unpleasant.  But it's so rare we barge in assuming it's
 	// fine.  It could also shrink but that falls out naturally.
 	maxbytes := len(s) // length of b
 	nbytes := 0        // number of bytes encoded in b
 	b := make([]byte, maxbytes)
 	for i := 0; i < len(s); {
 		wid := 1
 		r := rune(s[i])
 		if r >= utf8.RuneSelf {
 			r, wid = utf8.DecodeRune(s[i:])
 		}
 		r = mapping(r)
 		if r >= 0 {
 			rl := utf8.RuneLen(r)
 			if rl < 0 {
 				rl = len(string(utf8.RuneError))
 			}
 			if nbytes+rl > maxbytes {
 				// Grow the buffer.
 				maxbytes = maxbytes*2 + utf8.UTFMax
 				nb := make([]byte, maxbytes)
 				copy(nb, b[0:nbytes])
 				b = nb
 			}
 			nbytes += utf8.EncodeRune(b[nbytes:maxbytes], r)
 		}
 		i += wid
 	}
 	return b[0:nbytes]
 }

 // Repeat returns a new byte slice consisting of count copies of b.
 func Repeat(b []byte, count int) []byte {
 	nb := make([]byte, len(b)*count)
 	bp := copy(nb, b)
 	for bp < len(nb) {
 		copy(nb[bp:], nb[:bp])
 		bp *= 2
 	}
 	return nb
 }

 // ToUpper returns a copy of the byte slice s with all Unicode letters mapped to their upper case.
 func ToUpper(s []byte) []byte { return Map(unicode.ToUpper, s) }

 // ToLower returns a copy of the byte slice s with all Unicode letters mapped to their lower case.
 func ToLower(s []byte) []byte { return Map(unicode.ToLower, s) }

 // ToTitle returns a copy of the byte slice s with all Unicode letters mapped to their title case.
 func ToTitle(s []byte) []byte { return Map(unicode.ToTitle, s) }

 // ToUpperSpecial returns a copy of the byte slice s with all Unicode letters mapped to their
 // upper case, giving priority to the special casing rules.
 func ToUpperSpecial(_case unicode.SpecialCase, s []byte) []byte {
 	return Map(func(r rune) rune { return _case.ToUpper(r) }, s)
 }

 // ToLowerSpecial returns a copy of the byte slice s with all Unicode letters mapped to their
 // lower case, giving priority to the special casing rules.
 func ToLowerSpecial(_case unicode.SpecialCase, s []byte) []byte {
 	return Map(func(r rune) rune { return _case.ToLower(r) }, s)
 }

 // ToTitleSpecial returns a copy of the byte slice s with all Unicode letters mapped to their
 // title case, giving priority to the special casing rules.
 func ToTitleSpecial(_case unicode.SpecialCase, s []byte) []byte {
 	return Map(func(r rune) rune { return _case.ToTitle(r) }, s)
 }

 // isSeparator reports whether the rune could mark a word boundary.
 // TODO: update when package unicode captures more of the properties.
 func isSeparator(r rune) bool {
 	// ASCII alphanumerics and underscore are not separators
 	if r <= 0x7F {
 		switch {
 		case '0' <= r && r <= '9':
 			return false
 		case 'a' <= r && r <= 'z':
 			return false
 		case 'A' <= r && r <= 'Z':
 			return false
 		case r == '_':
 			return false
 		}
 		return true
 	}
 	// Letters and digits are not separators
 	if unicode.IsLetter(r) || unicode.IsDigit(r) {
 		return false
 	}
 	// Otherwise, all we can do for now is treat spaces as separators.
 	return unicode.IsSpace(r)
 }

 // Title returns a copy of s with all Unicode letters that begin words
 // mapped to their title case.
 //
 // BUG(rsc): The rule Title uses for word boundaries does not handle Unicode punctuation properly.
 func Title(s []byte) []byte {
 	// Use a closure here to remember state.
 	// Hackish but effective. Depends on Map scanning in order and calling
 	// the closure once per rune.
 	prev := ' '
 	return Map(
 		func(r rune) rune {
 			if isSeparator(prev) {
 				prev = r
 				return unicode.ToTitle(r)
 			}
 			prev = r
 			return r
 		},
 		s)
 }

 // TrimLeftFunc returns a subslice of s by slicing off all leading UTF-8-encoded
 // Unicode code points c that satisfy f(c).
 func TrimLeftFunc(s []byte, f func(r rune) bool) []byte {
 	i := indexFunc(s, f, false)
 	if i == -1 {
 		return nil
 	}
 	return s[i:]
 }

 // TrimRightFunc returns a subslice of s by slicing off all trailing UTF-8
 // encoded Unicode code points c that satisfy f(c).
 func TrimRightFunc(s []byte, f func(r rune) bool) []byte {
 	i := lastIndexFunc(s, f, false)
 	if i >= 0 && s[i] >= utf8.RuneSelf {
 		_, wid := utf8.DecodeRune(s[i:])
 		i += wid
 	} else {
 		i++
 	}
 	return s[0:i]
 }

 // TrimFunc returns a subslice of s by slicing off all leading and trailing
 // UTF-8-encoded Unicode code points c that satisfy f(c).
 func TrimFunc(s []byte, f func(r rune) bool) []byte {
 	return TrimRightFunc(TrimLeftFunc(s, f), f)
 }

 // TrimPrefix returns s without the provided leading prefix string.
 // If s doesn't start with prefix, s is returned unchanged.
 func TrimPrefix(s, prefix []byte) []byte {
 	if HasPrefix(s, prefix) {
 		return s[len(prefix):]
 	}
 	return s
 }

 // TrimSuffix returns s without the provided trailing suffix string.
 // If s doesn't end with suffix, s is returned unchanged.
 func TrimSuffix(s, suffix []byte) []byte {
 	if HasSuffix(s, suffix) {
 		return s[:len(s)-len(suffix)]
 	}
 	return s
 }

 // IndexFunc interprets s as a sequence of UTF-8-encoded Unicode code points.
 // It returns the byte index in s of the first Unicode
 // code point satisfying f(c), or -1 if none do.
 func IndexFunc(s []byte, f func(r rune) bool) int {
 	return indexFunc(s, f, true)
 }

 // LastIndexFunc interprets s as a sequence of UTF-8-encoded Unicode code points.
 // It returns the byte index in s of the last Unicode
 // code point satisfying f(c), or -1 if none do.
 func LastIndexFunc(s []byte, f func(r rune) bool) int {
 	return lastIndexFunc(s, f, true)
 }

 // indexFunc is the same as IndexFunc except that if
 // truth==false, the sense of the predicate function is
 // inverted.
 func indexFunc(s []byte, f func(r rune) bool, truth bool) int {
 	start := 0
 	for start < len(s) {
 		wid := 1
 		r := rune(s[start])
 		if r >= utf8.RuneSelf {
 			r, wid = utf8.DecodeRune(s[start:])
 		}
 		if f(r) == truth {
 			return start
 		}
 		start += wid
 	}
 	return -1
 }

 // lastIndexFunc is the same as LastIndexFunc except that if
 // truth==false, the sense of the predicate function is
 // inverted.
 func lastIndexFunc(s []byte, f func(r rune) bool, truth bool) int {
 	for i := len(s); i > 0; {
 		r, size := rune(s[i-1]), 1
 		if r >= utf8.RuneSelf {
 			r, size = utf8.DecodeLastRune(s[0:i])
 		}
 		i -= size
 		if f(r) == truth {
 			return i
 		}
 	}
 	return -1
 }

 func makeCutsetFunc(cutset string) func(r rune) bool {
 	return func(r rune) bool {
 		for _, c := range cutset {
 			if c == r {
 				return true
 			}
 		}
 		return false
 	}
 }

 // Trim returns a subslice of s by slicing off all leading and
 // trailing UTF-8-encoded Unicode code points contained in cutset.
 func Trim(s []byte, cutset string) []byte {
 	return TrimFunc(s, makeCutsetFunc(cutset))
 }

 // TrimLeft returns a subslice of s by slicing off all leading
 // UTF-8-encoded Unicode code points contained in cutset.
 func TrimLeft(s []byte, cutset string) []byte {
 	return TrimLeftFunc(s, makeCutsetFunc(cutset))
 }

 // TrimRight returns a subslice of s by slicing off all trailing
 // UTF-8-encoded Unicode code points that are contained in cutset.
 func TrimRight(s []byte, cutset string) []byte {
 	return TrimRightFunc(s, makeCutsetFunc(cutset))
 }

 // TrimSpace returns a subslice of s by slicing off all leading and
 // trailing white space, as defined by Unicode.
 func TrimSpace(s []byte) []byte {
 	return TrimFunc(s, unicode.IsSpace)
 }

 // Runes returns a slice of runes (Unicode code points) equivalent to s.
 func Runes(s []byte) []rune {
 	t := make([]rune, utf8.RuneCount(s))
 	i := 0
 	for len(s) > 0 {
 		r, l := utf8.DecodeRune(s)
 		t[i] = r
 		i++
 		s = s[l:]
 	}
 	return t
 }

 // Replace returns a copy of the slice s with the first n
 // non-overlapping instances of old replaced by new.
 // If old is empty, it matches at the beginning of the slice
 // and after each UTF-8 sequence, yielding up to k+1 replacements
 // for a k-rune slice.
 // If n < 0, there is no limit on the number of replacements.
 func Replace(s, old, new []byte, n int) []byte {
 	m := 0
 	if n != 0 {
 		// Compute number of replacements.
 		m = Count(s, old)
 	}
 	if m == 0 {
 		// Just return a copy.
 		return append([]byte(nil), s...)
 	}
 	if n < 0 || m < n {
 		n = m
 	}

 	// Apply replacements to buffer.
 	t := make([]byte, len(s)+n*(len(new)-len(old)))
 	w := 0
 	start := 0
 	for i := 0; i < n; i++ {
 		j := start
 		if len(old) == 0 {
 			if i > 0 {
 				_, wid := utf8.DecodeRune(s[start:])
 				j += wid
 			}
 		} else {
 			j += Index(s[start:], old)
 		}
 		w += copy(t[w:], s[start:j])
 		w += copy(t[w:], new)
 		start = j + len(old)
 	}
 	w += copy(t[w:], s[start:])
 	return t[0:w]
 }

 // EqualFold reports whether s and t, interpreted as UTF-8 strings,
 // are equal under Unicode case-folding.
 func EqualFold(s, t []byte) bool {
 	for len(s) != 0 && len(t) != 0 {
 		// Extract first rune from each.
 		var sr, tr rune
 		if s[0] < utf8.RuneSelf {
 			sr, s = rune(s[0]), s[1:]
 		} else {
 			r, size := utf8.DecodeRune(s)
 			sr, s = r, s[size:]
 		}
 		if t[0] < utf8.RuneSelf {
 			tr, t = rune(t[0]), t[1:]
 		} else {
 			r, size := utf8.DecodeRune(t)
 			tr, t = r, t[size:]
 		}

 		// If they match, keep going; if not, return false.

 		// Easy case.
 		if tr == sr {
 			continue
 		}

 		// Make sr < tr to simplify what follows.
 		if tr < sr {
 			tr, sr = sr, tr
 		}
 		// Fast check for ASCII.
 		if tr < utf8.RuneSelf && 'A' <= sr && sr <= 'Z' {
 			// ASCII, and sr is upper case.  tr must be lower case.
 			if tr == sr+'a'-'A' {
 				continue
 			}
 			return false
 		}

 		// General case.  SimpleFold(x) returns the next equivalent rune > x
 		// or wraps around to smaller values.
 		r := unicode.SimpleFold(sr)
 		for r != sr && r < tr {
 			r = unicode.SimpleFold(r)
 		}
 		if r == tr {
 			continue
 		}
 		return false
 	}

 	// One string is empty.  Are both?
 	return len(s) == len(t)
 }
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// Package bytes implements functions for the manipulation of byte slices.
	// It is analogous to the facilities of the strings package.
	package bytes

	import (
	"unicode"
	"unicode/utf8"
	)

	func equalPortable(a, b []byte) bool {
	if len(a) != len(b) {
	return false
	}
	for i, c := range a {
	if c != b[i] {
	return false
	}
	}
	return true
	}

	// explode splits s into a slice of UTF-8 sequences, one per Unicode code point (still slices of bytes),
	// up to a maximum of n byte slices. Invalid UTF-8 sequences are chopped into individual bytes.
	func explode(s []byte, n int) [][]byte {
	if n <= 0 {
	n = len(s)
	}
	a := make([][]byte, n)
	var size int
	na := 0
	for len(s) > 0 {
	if na+1 >= n {
	a[na] = s
	na++
	break
	}
	_, size = utf8.DecodeRune(s)
	a[na] = s[0:size]
	s = s[size:]
	na++
	}
	return a[0:na]
	}

	// Count counts the number of non-overlapping instances of sep in s.
	// If sep is an empty slice, Count returns 1 + the number of Unicode code points in s.
	func Count(s, sep []byte) int {
	n := len(sep)
	if n == 0 {
	return utf8.RuneCount(s) + 1
	}
	if n > len(s) {
	return 0
	}
	count := 0
	c := sep[0]
	i := 0
	t := s[:len(s)-n+1]
	for i < len(t) {
	if t[i] != c {
	o := IndexByte(t[i:], c)
	if o < 0 {
	break
	}
	i += o
	}
	if n == 1 \|\| Equal(s[i:i+n], sep) {
	count++
	i += n
	continue
	}
	i++
	}
	return count
	}

	// Contains reports whether subslice is within b.
	func Contains(b, subslice []byte) bool {
	return Index(b, subslice) != -1
	}

	// Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
	func Index(s, sep []byte) int {
	n := len(sep)
	if n == 0 {
	return 0
	}
	if n > len(s) {
	return -1
	}
	c := sep[0]
	if n == 1 {
	return IndexByte(s, c)
	}
	i := 0
	t := s[:len(s)-n+1]
	for i < len(t) {
	if t[i] != c {
	o := IndexByte(t[i:], c)
	if o < 0 {
	break
	}
	i += o
	}
	if Equal(s[i:i+n], sep) {
	return i
	}
	i++
	}
	return -1
	}

	func indexBytePortable(s []byte, c byte) int {
	for i, b := range s {
	if b == c {
	return i
	}
	}
	return -1
	}

	// LastIndex returns the index of the last instance of sep in s, or -1 if sep is not present in s.
	func LastIndex(s, sep []byte) int {
	n := len(sep)
	if n == 0 {
	return len(s)
	}
	c := sep[0]
	for i := len(s) - n; i >= 0; i-- {
	if s[i] == c && (n == 1 \|\| Equal(s[i:i+n], sep)) {
	return i
	}
	}
	return -1
	}

	// LastIndexByte returns the index of the last instance of c in s, or -1 if c is not present in s.
	func LastIndexByte(s []byte, c byte) int {
	for i := len(s) - 1; i >= 0; i-- {
	if s[i] == c {
	return i
	}
	}
	return -1
	}

	// IndexRune interprets s as a sequence of UTF-8-encoded Unicode code points.
	// It returns the byte index of the first occurrence in s of the given rune.
	// It returns -1 if rune is not present in s.
	func IndexRune(s []byte, r rune) int {
	for i := 0; i < len(s); {
	r1, size := utf8.DecodeRune(s[i:])
	if r == r1 {
	return i
	}
	i += size
	}
	return -1
	}

	// IndexAny interprets s as a sequence of UTF-8-encoded Unicode code points.
	// It returns the byte index of the first occurrence in s of any of the Unicode
	// code points in chars. It returns -1 if chars is empty or if there is no code
	// point in common.
	func IndexAny(s []byte, chars string) int {
	if len(chars) > 0 {
	var r rune
	var width int
	for i := 0; i < len(s); i += width {
	r = rune(s[i])
	if r < utf8.RuneSelf {
	width = 1
	} else {
	r, width = utf8.DecodeRune(s[i:])
	}
	for _, ch := range chars {
	if r == ch {
	return i
	}
	}
	}
	}
	return -1
	}

	// LastIndexAny interprets s as a sequence of UTF-8-encoded Unicode code
	// points. It returns the byte index of the last occurrence in s of any of
	// the Unicode code points in chars. It returns -1 if chars is empty or if
	// there is no code point in common.
	func LastIndexAny(s []byte, chars string) int {
	if len(chars) > 0 {
	for i := len(s); i > 0; {
	r, size := utf8.DecodeLastRune(s[0:i])
	i -= size
	for _, ch := range chars {
	if r == ch {
	return i
	}
	}
	}
	}
	return -1
	}

	// Generic split: splits after each instance of sep,
	// including sepSave bytes of sep in the subslices.
	func genSplit(s, sep []byte, sepSave, n int) [][]byte {
	if n == 0 {
	return nil
	}
	if len(sep) == 0 {
	return explode(s, n)
	}
	if n < 0 {
	n = Count(s, sep) + 1
	}
	c := sep[0]
	start := 0
	a := make([][]byte, n)
	na := 0
	for i := 0; i+len(sep) <= len(s) && na+1 < n; i++ {
	if s[i] == c && (len(sep) == 1 \|\| Equal(s[i:i+len(sep)], sep)) {
	a[na] = s[start : i+sepSave]
	na++
	start = i + len(sep)
	i += len(sep) - 1
	}
	}
	a[na] = s[start:]
	return a[0 : na+1]
	}

	// SplitN slices s into subslices separated by sep and returns a slice of
	// the subslices between those separators.
	// If sep is empty, SplitN splits after each UTF-8 sequence.
	// The count determines the number of subslices to return:
	// n > 0: at most n subslices; the last subslice will be the unsplit remainder.
	// n == 0: the result is nil (zero subslices)
	// n < 0: all subslices
	func SplitN(s, sep []byte, n int) [][]byte { return genSplit(s, sep, 0, n) }

	// SplitAfterN slices s into subslices after each instance of sep and
	// returns a slice of those subslices.
	// If sep is empty, SplitAfterN splits after each UTF-8 sequence.
	// The count determines the number of subslices to return:
	// n > 0: at most n subslices; the last subslice will be the unsplit remainder.
	// n == 0: the result is nil (zero subslices)
	// n < 0: all subslices
	func SplitAfterN(s, sep []byte, n int) [][]byte {
	return genSplit(s, sep, len(sep), n)
	}

	// Split slices s into all subslices separated by sep and returns a slice of
	// the subslices between those separators.
	// If sep is empty, Split splits after each UTF-8 sequence.
	// It is equivalent to SplitN with a count of -1.
	func Split(s, sep []byte) [][]byte { return genSplit(s, sep, 0, -1) }

	// SplitAfter slices s into all subslices after each instance of sep and
	// returns a slice of those subslices.
	// If sep is empty, SplitAfter splits after each UTF-8 sequence.
	// It is equivalent to SplitAfterN with a count of -1.
	func SplitAfter(s, sep []byte) [][]byte {
	return genSplit(s, sep, len(sep), -1)
	}

	// Fields splits the slice s around each instance of one or more consecutive white space
	// characters, returning a slice of subslices of s or an empty list if s contains only white space.
	func Fields(s []byte) [][]byte {
	return FieldsFunc(s, unicode.IsSpace)
	}

	// FieldsFunc interprets s as a sequence of UTF-8-encoded Unicode code points.
	// It splits the slice s at each run of code points c satisfying f(c) and
	// returns a slice of subslices of s. If all code points in s satisfy f(c), or
	// len(s) == 0, an empty slice is returned.
	// FieldsFunc makes no guarantees about the order in which it calls f(c).
	// If f does not return consistent results for a given c, FieldsFunc may crash.
	func FieldsFunc(s []byte, f func(rune) bool) [][]byte {
	n := 0
	inField := false
	for i := 0; i < len(s); {
	r, size := utf8.DecodeRune(s[i:])
	wasInField := inField
	inField = !f(r)
	if inField && !wasInField {
	n++
	}
	i += size
	}

	a := make([][]byte, n)
	na := 0
	fieldStart := -1
	for i := 0; i <= len(s) && na < n; {
	r, size := utf8.DecodeRune(s[i:])
	if fieldStart < 0 && size > 0 && !f(r) {
	fieldStart = i
	i += size
	continue
	}
	if fieldStart >= 0 && (size == 0 \|\| f(r)) {
	a[na] = s[fieldStart:i]
	na++
	fieldStart = -1
	}
	if size == 0 {
	break
	}
	i += size
	}
	return a[0:na]
	}

	// Join concatenates the elements of s to create a new byte slice. The separator
	// sep is placed between elements in the resulting slice.
	func Join(s [][]byte, sep []byte) []byte {
	if len(s) == 0 {
	return []byte{}
	}
	if len(s) == 1 {
	// Just return a copy.
	return append([]byte(nil), s[0]...)
	}
	n := len(sep) * (len(s) - 1)
	for _, v := range s {
	n += len(v)
	}

	b := make([]byte, n)
	bp := copy(b, s[0])
	for _, v := range s[1:] {
	bp += copy(b[bp:], sep)
	bp += copy(b[bp:], v)
	}
	return b
	}

	// HasPrefix tests whether the byte slice s begins with prefix.
	func HasPrefix(s, prefix []byte) bool {
	return len(s) >= len(prefix) && Equal(s[0:len(prefix)], prefix)
	}

	// HasSuffix tests whether the byte slice s ends with suffix.
	func HasSuffix(s, suffix []byte) bool {
	return len(s) >= len(suffix) && Equal(s[len(s)-len(suffix):], suffix)
	}

	// Map returns a copy of the byte slice s with all its characters modified
	// according to the mapping function. If mapping returns a negative value, the character is
	// dropped from the string with no replacement. The characters in s and the
	// output are interpreted as UTF-8-encoded Unicode code points.
	func Map(mapping func(r rune) rune, s []byte) []byte {
	// In the worst case, the slice can grow when mapped, making
	// things unpleasant. But it's so rare we barge in assuming it's
	// fine. It could also shrink but that falls out naturally.
	maxbytes := len(s) // length of b
	nbytes := 0 // number of bytes encoded in b
	b := make([]byte, maxbytes)
	for i := 0; i < len(s); {
	wid := 1
	r := rune(s[i])
	if r >= utf8.RuneSelf {
	r, wid = utf8.DecodeRune(s[i:])
	}
	r = mapping(r)
	if r >= 0 {
	rl := utf8.RuneLen(r)
	if rl < 0 {
	rl = len(string(utf8.RuneError))
	}
	if nbytes+rl > maxbytes {
	// Grow the buffer.
	maxbytes = maxbytes*2 + utf8.UTFMax
	nb := make([]byte, maxbytes)
	copy(nb, b[0:nbytes])
	b = nb
	}
	nbytes += utf8.EncodeRune(b[nbytes:maxbytes], r)
	}
	i += wid
	}
	return b[0:nbytes]
	}

	// Repeat returns a new byte slice consisting of count copies of b.
	func Repeat(b []byte, count int) []byte {
	nb := make([]byte, len(b)*count)
	bp := copy(nb, b)
	for bp < len(nb) {
	copy(nb[bp:], nb[:bp])
	bp *= 2
	}
	return nb
	}

	// ToUpper returns a copy of the byte slice s with all Unicode letters mapped to their upper case.
	func ToUpper(s []byte) []byte { return Map(unicode.ToUpper, s) }

	// ToLower returns a copy of the byte slice s with all Unicode letters mapped to their lower case.
	func ToLower(s []byte) []byte { return Map(unicode.ToLower, s) }

	// ToTitle returns a copy of the byte slice s with all Unicode letters mapped to their title case.
	func ToTitle(s []byte) []byte { return Map(unicode.ToTitle, s) }

	// ToUpperSpecial returns a copy of the byte slice s with all Unicode letters mapped to their
	// upper case, giving priority to the special casing rules.
	func ToUpperSpecial(_case unicode.SpecialCase, s []byte) []byte {
	return Map(func(r rune) rune { return _case.ToUpper(r) }, s)
	}

	// ToLowerSpecial returns a copy of the byte slice s with all Unicode letters mapped to their
	// lower case, giving priority to the special casing rules.
	func ToLowerSpecial(_case unicode.SpecialCase, s []byte) []byte {
	return Map(func(r rune) rune { return _case.ToLower(r) }, s)
	}

	// ToTitleSpecial returns a copy of the byte slice s with all Unicode letters mapped to their
	// title case, giving priority to the special casing rules.
	func ToTitleSpecial(_case unicode.SpecialCase, s []byte) []byte {
	return Map(func(r rune) rune { return _case.ToTitle(r) }, s)
	}

	// isSeparator reports whether the rune could mark a word boundary.
	// TODO: update when package unicode captures more of the properties.
	func isSeparator(r rune) bool {
	// ASCII alphanumerics and underscore are not separators
	if r <= 0x7F {
	switch {
	case '0' <= r && r <= '9':
	return false
	case 'a' <= r && r <= 'z':
	return false
	case 'A' <= r && r <= 'Z':
	return false
	case r == '_':
	return false
	}
	return true
	}
	// Letters and digits are not separators
	if unicode.IsLetter(r) \|\| unicode.IsDigit(r) {
	return false
	}
	// Otherwise, all we can do for now is treat spaces as separators.
	return unicode.IsSpace(r)
	}

	// Title returns a copy of s with all Unicode letters that begin words
	// mapped to their title case.
	//
	// BUG(rsc): The rule Title uses for word boundaries does not handle Unicode punctuation properly.
	func Title(s []byte) []byte {
	// Use a closure here to remember state.
	// Hackish but effective. Depends on Map scanning in order and calling
	// the closure once per rune.
	prev := ' '
	return Map(
	func(r rune) rune {
	if isSeparator(prev) {
	prev = r
	return unicode.ToTitle(r)
	}
	prev = r
	return r
	},
	s)
	}

	// TrimLeftFunc returns a subslice of s by slicing off all leading UTF-8-encoded
	// Unicode code points c that satisfy f(c).
	func TrimLeftFunc(s []byte, f func(r rune) bool) []byte {
	i := indexFunc(s, f, false)
	if i == -1 {
	return nil
	}
	return s[i:]
	}

	// TrimRightFunc returns a subslice of s by slicing off all trailing UTF-8
	// encoded Unicode code points c that satisfy f(c).
	func TrimRightFunc(s []byte, f func(r rune) bool) []byte {
	i := lastIndexFunc(s, f, false)
	if i >= 0 && s[i] >= utf8.RuneSelf {
	_, wid := utf8.DecodeRune(s[i:])
	i += wid
	} else {
	i++
	}
	return s[0:i]
	}

	// TrimFunc returns a subslice of s by slicing off all leading and trailing
	// UTF-8-encoded Unicode code points c that satisfy f(c).
	func TrimFunc(s []byte, f func(r rune) bool) []byte {
	return TrimRightFunc(TrimLeftFunc(s, f), f)
	}

	// TrimPrefix returns s without the provided leading prefix string.
	// If s doesn't start with prefix, s is returned unchanged.
	func TrimPrefix(s, prefix []byte) []byte {
	if HasPrefix(s, prefix) {
	return s[len(prefix):]
	}
	return s
	}

	// TrimSuffix returns s without the provided trailing suffix string.
	// If s doesn't end with suffix, s is returned unchanged.
	func TrimSuffix(s, suffix []byte) []byte {
	if HasSuffix(s, suffix) {
	return s[:len(s)-len(suffix)]
	}
	return s
	}

	// IndexFunc interprets s as a sequence of UTF-8-encoded Unicode code points.
	// It returns the byte index in s of the first Unicode
	// code point satisfying f(c), or -1 if none do.
	func IndexFunc(s []byte, f func(r rune) bool) int {
	return indexFunc(s, f, true)
	}

	// LastIndexFunc interprets s as a sequence of UTF-8-encoded Unicode code points.
	// It returns the byte index in s of the last Unicode
	// code point satisfying f(c), or -1 if none do.
	func LastIndexFunc(s []byte, f func(r rune) bool) int {
	return lastIndexFunc(s, f, true)
	}

	// indexFunc is the same as IndexFunc except that if
	// truth==false, the sense of the predicate function is
	// inverted.
	func indexFunc(s []byte, f func(r rune) bool, truth bool) int {
	start := 0
	for start < len(s) {
	wid := 1
	r := rune(s[start])
	if r >= utf8.RuneSelf {
	r, wid = utf8.DecodeRune(s[start:])
	}
	if f(r) == truth {
	return start
	}
	start += wid
	}
	return -1
	}

	// lastIndexFunc is the same as LastIndexFunc except that if
	// truth==false, the sense of the predicate function is
	// inverted.
	func lastIndexFunc(s []byte, f func(r rune) bool, truth bool) int {
	for i := len(s); i > 0; {
	r, size := rune(s[i-1]), 1
	if r >= utf8.RuneSelf {
	r, size = utf8.DecodeLastRune(s[0:i])
	}
	i -= size
	if f(r) == truth {
	return i
	}
	}
	return -1
	}

	func makeCutsetFunc(cutset string) func(r rune) bool {
	return func(r rune) bool {
	for _, c := range cutset {
	if c == r {
	return true
	}
	}
	return false
	}
	}

	// Trim returns a subslice of s by slicing off all leading and
	// trailing UTF-8-encoded Unicode code points contained in cutset.
	func Trim(s []byte, cutset string) []byte {
	return TrimFunc(s, makeCutsetFunc(cutset))
	}

	// TrimLeft returns a subslice of s by slicing off all leading
	// UTF-8-encoded Unicode code points contained in cutset.
	func TrimLeft(s []byte, cutset string) []byte {
	return TrimLeftFunc(s, makeCutsetFunc(cutset))
	}

	// TrimRight returns a subslice of s by slicing off all trailing
	// UTF-8-encoded Unicode code points that are contained in cutset.
	func TrimRight(s []byte, cutset string) []byte {
	return TrimRightFunc(s, makeCutsetFunc(cutset))
	}

	// TrimSpace returns a subslice of s by slicing off all leading and
	// trailing white space, as defined by Unicode.
	func TrimSpace(s []byte) []byte {
	return TrimFunc(s, unicode.IsSpace)
	}

	// Runes returns a slice of runes (Unicode code points) equivalent to s.
	func Runes(s []byte) []rune {
	t := make([]rune, utf8.RuneCount(s))
	i := 0
	for len(s) > 0 {
	r, l := utf8.DecodeRune(s)
	t[i] = r
	i++
	s = s[l:]
	}
	return t
	}

	// Replace returns a copy of the slice s with the first n
	// non-overlapping instances of old replaced by new.
	// If old is empty, it matches at the beginning of the slice
	// and after each UTF-8 sequence, yielding up to k+1 replacements
	// for a k-rune slice.
	// If n < 0, there is no limit on the number of replacements.
	func Replace(s, old, new []byte, n int) []byte {
	m := 0
	if n != 0 {
	// Compute number of replacements.
	m = Count(s, old)
	}
	if m == 0 {
	// Just return a copy.
	return append([]byte(nil), s...)
	}
	if n < 0 \|\| m < n {
	n = m
	}

	// Apply replacements to buffer.
	t := make([]byte, len(s)+n*(len(new)-len(old)))
	w := 0
	start := 0
	for i := 0; i < n; i++ {
	j := start
	if len(old) == 0 {
	if i > 0 {
	_, wid := utf8.DecodeRune(s[start:])
	j += wid
	}
	} else {
	j += Index(s[start:], old)
	}
	w += copy(t[w:], s[start:j])
	w += copy(t[w:], new)
	start = j + len(old)
	}
	w += copy(t[w:], s[start:])
	return t[0:w]
	}

	// EqualFold reports whether s and t, interpreted as UTF-8 strings,
	// are equal under Unicode case-folding.
	func EqualFold(s, t []byte) bool {
	for len(s) != 0 && len(t) != 0 {
	// Extract first rune from each.
	var sr, tr rune
	if s[0] < utf8.RuneSelf {
	sr, s = rune(s[0]), s[1:]
	} else {
	r, size := utf8.DecodeRune(s)
	sr, s = r, s[size:]
	}
	if t[0] < utf8.RuneSelf {
	tr, t = rune(t[0]), t[1:]
	} else {
	r, size := utf8.DecodeRune(t)
	tr, t = r, t[size:]
	}

	// If they match, keep going; if not, return false.

	// Easy case.
	if tr == sr {
	continue
	}

	// Make sr < tr to simplify what follows.
	if tr < sr {
	tr, sr = sr, tr
	}
	// Fast check for ASCII.
	if tr < utf8.RuneSelf && 'A' <= sr && sr <= 'Z' {
	// ASCII, and sr is upper case. tr must be lower case.
	if tr == sr+'a'-'A' {
	continue
	}
	return false
	}

	// General case. SimpleFold(x) returns the next equivalent rune > x
	// or wraps around to smaller values.
	r := unicode.SimpleFold(sr)
	for r != sr && r < tr {
	r = unicode.SimpleFold(r)
	}
	if r == tr {
	continue
	}
	return false
	}

	// One string is empty. Are both?
	return len(s) == len(t)
	}