// 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 (
"internal/bytealg"
"unicode"
"unicode/utf8"
)
// Equal reports whether a and b
// are the same length and contain the same bytes.
// A nil argument is equivalent to an empty slice.
func Equal(a, b []byte) bool {
// Neither cmd/compile nor gccgo allocates for these string conversions.
return string(a) == string(b)
}
// Compare returns an integer comparing two byte slices lexicographically.
// The result will be 0 if a==b, -1 if a < b, and +1 if a > b.
// A nil argument is equivalent to an empty slice.
func Compare(a, b []byte) int {
return bytealg.Compare(a, b)
}
// 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: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 UTF-8-encoded code points in s.
func Count(s, sep []byte) int {
// special case
if len(sep) == 0 {
return utf8.RuneCount(s) + 1
}
if len(sep) == 1 {
return bytealg.Count(s, sep[0])
}
n := 0
for {
i := Index(s, sep)
if i == -1 {
return n
}
n++
s = s[i+len(sep):]
}
}
// Contains reports whether subslice is within b.
func Contains(b, subslice []byte) bool {
return Index(b, subslice) != -1
}
// ContainsAny reports whether any of the UTF-8-encoded code points in chars are within b.
func ContainsAny(b []byte, chars string) bool {
return IndexAny(b, chars) >= 0
}
// ContainsRune reports whether the rune is contained in the UTF-8-encoded byte slice b.
func ContainsRune(b []byte, r rune) bool {
return IndexRune(b, r) >= 0
}
// IndexByte returns the index of the first instance of c in b, or -1 if c is not present in b.
func IndexByte(b []byte, c byte) int {
return bytealg.IndexByte(b, c)
}
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)
switch {
case n == 0:
return len(s)
case n == 1:
return LastIndexByte(s, sep[0])
case n == len(s):
if Equal(s, sep) {
return 0
}
return -1
case n > len(s):
return -1
}
// Rabin-Karp search from the end of the string
hashss, pow := hashStrRev(sep)
last := len(s) - n
var h uint32
for i := len(s) - 1; i >= last; i-- {
h = h*primeRK + uint32(s[i])
}
if h == hashss && Equal(s[last:], sep) {
return last
}
for i := last - 1; i >= 0; i-- {
h *= primeRK
h += uint32(s[i])
h -= pow * uint32(s[i+n])
if h == hashss && 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 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.
// If r is utf8.RuneError, it returns the first instance of any
// invalid UTF-8 byte sequence.
func IndexRune(s []byte, r rune) int {
switch {
case 0 <= r && r < utf8.RuneSelf:
return IndexByte(s, byte(r))
case r == utf8.RuneError:
for i := 0; i < len(s); {
r1, n := utf8.DecodeRune(s[i:])
if r1 == utf8.RuneError {
return i
}
i += n
}
return -1
case !utf8.ValidRune(r):
return -1
default:
var b [utf8.UTFMax]byte
n := utf8.EncodeRune(b[:], r)
return Index(s, b[:n])
}
}
// 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 chars == "" {
// Avoid scanning all of s.
return -1
}
if len(s) > 8 {
if as, isASCII := makeASCIISet(chars); isASCII {
for i, c := range s {
if as.contains(c) {
return i
}
}
return -1
}
}
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 chars == "" {
// Avoid scanning all of s.
return -1
}
if len(s) > 8 {
if as, isASCII := makeASCIISet(chars); isASCII {
for i := len(s) - 1; i >= 0; i-- {
if as.contains(s[i]) {
return i
}
}
return -1
}
}
for i := len(s); i > 0; {
r, size := utf8.DecodeLastRune(s[:i])
i -= size
for _, c := range chars {
if r == c {
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
}
a := make([][]byte, n)
n--
i := 0
for i < n {
m := Index(s, sep)
if m < 0 {
break
}
a[i] = s[: m+sepSave : m+sepSave]
s = s[m+len(sep):]
i++
}
a[i] = s
return a[:i+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)
}
var asciiSpace = [256]uint8{'\t': 1, '\n': 1, '\v': 1, '\f': 1, '\r': 1, ' ': 1}
// Fields interprets s as a sequence of UTF-8-encoded code points.
// It splits the slice s around each instance of one or more consecutive white space
// characters, as defined by unicode.IsSpace, returning a slice of subslices of s or an
// empty slice if s contains only white space.
func Fields(s []byte) [][]byte {
// First count the fields.
// This is an exact count if s is ASCII, otherwise it is an approximation.
n := 0
wasSpace := 1
// setBits is used to track which bits are set in the bytes of s.
setBits := uint8(0)
for i := 0; i < len(s); i++ {
r := s[i]
setBits |= r
isSpace := int(asciiSpace[r])
n += wasSpace & ^isSpace
wasSpace = isSpace
}
if setBits >= utf8.RuneSelf {
// Some runes in the input slice are not ASCII.
return FieldsFunc(s, unicode.IsSpace)
}
// ASCII fast path
a := make([][]byte, n)
na := 0
fieldStart := 0
i := 0
// Skip spaces in the front of the input.
for i < len(s) && asciiSpace[s[i]] != 0 {
i++
}
fieldStart = i
for i < len(s) {
if asciiSpace[s[i]] == 0 {
i++
continue
}
a[na] = s[fieldStart:i:i]
na++
i++
// Skip spaces in between fields.
for i < len(s) && asciiSpace[s[i]] != 0 {
i++
}
fieldStart = i
}
if fieldStart < len(s) { // Last field might end at EOF.
a[na] = s[fieldStart:len(s):len(s)]
}
return a
}
// FieldsFunc interprets s as a sequence of UTF-8-encoded 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 {
// A span is used to record a slice of s of the form s[start:end].
// The start index is inclusive and the end index is exclusive.
type span struct {
start int
end int
}
spans := make([]span, 0, 32)
// Find the field start and end indices.
wasField := false
fromIndex := 0
for i := 0; i < len(s); {
size := 1
r := rune(s[i])
if r >= utf8.RuneSelf {
r, size = utf8.DecodeRune(s[i:])
}
if f(r) {
if wasField {
spans = append(spans, span{start: fromIndex, end: i})
wasField = false
}
} else {
if !wasField {
fromIndex = i
wasField = true
}
}
i += size
}
// Last field might end at EOF.
if wasField {
spans = append(spans, span{fromIndex, len(s)})
}
// Create subslices from recorded field indices.
a := make([][]byte, len(spans))
for i, span := range spans {
a[i] = s[span.start:span.end:span.end]
}
return a
}
// 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 byte slice with no replacement. The characters in s and the
// output are interpreted as UTF-8-encoded 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.
//
// It panics if count is negative or if
// the result of (len(b) * count) overflows.
func Repeat(b []byte, count int) []byte {
if count == 0 {
return []byte{}
}
// Since we cannot return an error on overflow,
// we should panic if the repeat will generate
// an overflow.
// See Issue golang.org/issue/16237.
if count < 0 {
panic("bytes: negative Repeat count")
} else if len(b)*count/count != len(b) {
panic("bytes: Repeat count causes overflow")
}
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 {
isASCII, hasLower := true, false
for i := 0; i < len(s); i++ {
c := s[i]
if c >= utf8.RuneSelf {
isASCII = false
break
}
hasLower = hasLower || ('a' <= c && c <= 'z')
}
if isASCII { // optimize for ASCII-only byte slices.
if !hasLower {
// Just return a copy.
return append([]byte(""), s...)
}
b := make([]byte, len(s))
for i := 0; i < len(s); i++ {
c := s[i]
if 'a' <= c && c <= 'z' {
c -= 'a' - 'A'
}
b[i] = c
}
return b
}
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 {
isASCII, hasUpper := true, false
for i := 0; i < len(s); i++ {
c := s[i]
if c >= utf8.RuneSelf {
isASCII = false
break
}
hasUpper = hasUpper || ('A' <= c && c <= 'Z')
}
if isASCII { // optimize for ASCII-only byte slices.
if !hasUpper {
return append([]byte(""), s...)
}
b := make([]byte, len(s))
for i := 0; i < len(s); i++ {
c := s[i]
if 'A' <= c && c <= 'Z' {
c += 'a' - 'A'
}
b[i] = c
}
return b
}
return Map(unicode.ToLower, s)
}
// ToTitle treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters mapped to their title case.
func ToTitle(s []byte) []byte { return Map(unicode.ToTitle, s) }
// ToUpperSpecial treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters mapped to their
// upper case, giving priority to the special casing rules.
func ToUpperSpecial(c unicode.SpecialCase, s []byte) []byte {
return Map(c.ToUpper, s)
}
// ToLowerSpecial treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters mapped to their
// lower case, giving priority to the special casing rules.
func ToLowerSpecial(c unicode.SpecialCase, s []byte) []byte {
return Map(c.ToLower, s)
}
// ToTitleSpecial treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters mapped to their
// title case, giving priority to the special casing rules.
func ToTitleSpecial(c unicode.SpecialCase, s []byte) []byte {
return Map(c.ToTitle, s)
}
// ToValidUTF8 treats s as UTF-8-encoded bytes and returns a copy with each run of bytes
// representing invalid UTF-8 replaced with the bytes in replacement, which may be empty.
func ToValidUTF8(s, replacement []byte) []byte {
b := make([]byte, 0, len(s)+len(replacement))
invalid := false // previous byte was from an invalid UTF-8 sequence
for i := 0; i < len(s); {
c := s[i]
if c < utf8.RuneSelf {
i++
invalid = false
b = append(b, byte(c))
continue
}
_, wid := utf8.DecodeRune(s[i:])
if wid == 1 {
i++
if !invalid {
invalid = true
b = append(b, replacement...)
}
continue
}
invalid = false
b = append(b, s[i:i+wid]...)
i += wid
}
return b
}
// 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 treats s as UTF-8-encoded bytes and returns a copy 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 treats s as UTF-8-encoded bytes and returns a subslice of s by slicing off
// all leading UTF-8-encoded 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 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 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 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 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
}
// asciiSet is a 32-byte value, where each bit represents the presence of a
// given ASCII character in the set. The 128-bits of the lower 16 bytes,
// starting with the least-significant bit of the lowest word to the
// most-significant bit of the highest word, map to the full range of all
// 128 ASCII characters. The 128-bits of the upper 16 bytes will be zeroed,
// ensuring that any non-ASCII character will be reported as not in the set.
type asciiSet [8]uint32
// makeASCIISet creates a set of ASCII characters and reports whether all
// characters in chars are ASCII.
func makeASCIISet(chars string) (as asciiSet, ok bool) {
for i := 0; i < len(chars); i++ {
c := chars[i]
if c >= utf8.RuneSelf {
return as, false
}
as[c>>5] |= 1 << uint(c&31)
}
return as, true
}
// contains reports whether c is inside the set.
func (as *asciiSet) contains(c byte) bool {
return (as[c>>5] & (1 << uint(c&31))) != 0
}
func makeCutsetFunc(cutset string) func(r rune) bool {
if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
return func(r rune) bool {
return r == rune(cutset[0])
}
}
if as, isASCII := makeASCIISet(cutset); isASCII {
return func(r rune) bool {
return r < utf8.RuneSelf && as.contains(byte(r))
}
}
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 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 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 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 {
// Fast path for ASCII: look for the first ASCII non-space byte
start := 0
for ; start < len(s); start++ {
c := s[start]
if c >= utf8.RuneSelf {
// If we run into a non-ASCII byte, fall back to the
// slower unicode-aware method on the remaining bytes
return TrimFunc(s[start:], unicode.IsSpace)
}
if asciiSpace[c] == 0 {
break
}
}
// Now look for the first ASCII non-space byte from the end
stop := len(s)
for ; stop > start; stop-- {
c := s[stop-1]
if c >= utf8.RuneSelf {
return TrimFunc(s[start:stop], unicode.IsSpace)
}
if asciiSpace[c] == 0 {
break
}
}
// At this point s[start:stop] starts and ends with an ASCII
// non-space bytes, so we're done. Non-ASCII cases have already
// been handled above.
if start == stop {
// Special case to preserve previous TrimLeftFunc behavior,
// returning nil instead of empty slice if all spaces.
return nil
}
return s[start:stop]
}
// Runes interprets s as a sequence of UTF-8-encoded code points.
// It 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]
}
// ReplaceAll returns a copy of the slice s with all
// 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.
func ReplaceAll(s, old, new []byte) []byte {
return Replace(s, old, new, -1)
}
// 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 {
// ASCII only, sr/tr must be upper/lower case
if 'A' <= sr && sr <= 'Z' && 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)
}
// 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)
switch {
case n == 0:
return 0
case n == 1:
return IndexByte(s, sep[0])
case n == len(s):
if Equal(sep, s) {
return 0
}
return -1
case n > len(s):
return -1
case n <= bytealg.MaxLen:
// Use brute force when s and sep both are small
if len(s) <= bytealg.MaxBruteForce {
return bytealg.Index(s, sep)
}
c0 := sep[0]
c1 := sep[1]
i := 0
t := len(s) - n + 1
fails := 0
for i < t {
if s[i] != c0 {
// IndexByte is faster than bytealg.Index, so use it as long as
// we're not getting lots of false positives.
o := IndexByte(s[i:t], c0)
if o < 0 {
return -1
}
i += o
}
if s[i+1] == c1 && Equal(s[i:i+n], sep) {
return i
}
fails++
i++
// Switch to bytealg.Index when IndexByte produces too many false positives.
if fails > bytealg.Cutover(i) {
r := bytealg.Index(s[i:], sep)
if r >= 0 {
return r + i
}
return -1
}
}
return -1
}
c0 := sep[0]
c1 := sep[1]
i := 0
fails := 0
t := len(s) - n + 1
for i < t {
if s[i] != c0 {
o := IndexByte(s[i:t], c0)
if o < 0 {
break
}
i += o
}
if s[i+1] == c1 && Equal(s[i:i+n], sep) {
return i
}
i++
fails++
if fails >= 4+i>>4 && i < t {
// Give up on IndexByte, it isn't skipping ahead
// far enough to be better than Rabin-Karp.
// Experiments (using IndexPeriodic) suggest
// the cutover is about 16 byte skips.
// TODO: if large prefixes of sep are matching
// we should cutover at even larger average skips,
// because Equal becomes that much more expensive.
// This code does not take that effect into account.
j := indexRabinKarp(s[i:], sep)
if j < 0 {
return -1
}
return i + j
}
}
return -1
}
func indexRabinKarp(s, sep []byte) int {
// Rabin-Karp search
hashsep, pow := hashStr(sep)
n := len(sep)
var h uint32
for i := 0; i < n; i++ {
h = h*primeRK + uint32(s[i])
}
if h == hashsep && Equal(s[:n], sep) {
return 0
}
for i := n; i < len(s); {
h *= primeRK
h += uint32(s[i])
h -= pow * uint32(s[i-n])
i++
if h == hashsep && Equal(s[i-n:i], sep) {
return i - n
}
}
return -1
}
// primeRK is the prime base used in Rabin-Karp algorithm.
const primeRK = 16777619
// hashStr returns the hash and the appropriate multiplicative
// factor for use in Rabin-Karp algorithm.
func hashStr(sep []byte) (uint32, uint32) {
hash := uint32(0)
for i := 0; i < len(sep); i++ {
hash = hash*primeRK + uint32(sep[i])
}
var pow, sq uint32 = 1, primeRK
for i := len(sep); i > 0; i >>= 1 {
if i&1 != 0 {
pow *= sq
}
sq *= sq
}
return hash, pow
}
// hashStrRev returns the hash of the reverse of sep and the
// appropriate multiplicative factor for use in Rabin-Karp algorithm.
func hashStrRev(sep []byte) (uint32, uint32) {
hash := uint32(0)
for i := len(sep) - 1; i >= 0; i-- {
hash = hash*primeRK + uint32(sep[i])
}
var pow, sq uint32 = 1, primeRK
for i := len(sep); i > 0; i >>= 1 {
if i&1 != 0 {
pow *= sq
}
sq *= sq
}
return hash, pow
}
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