summaryrefslogtreecommitdiff
path: root/src/strings/strings.go
diff options
context:
space:
mode:
Diffstat (limited to 'src/strings/strings.go')
-rw-r--r--src/strings/strings.go762
1 files changed, 762 insertions, 0 deletions
diff --git a/src/strings/strings.go b/src/strings/strings.go
new file mode 100644
index 000000000..27d384983
--- /dev/null
+++ b/src/strings/strings.go
@@ -0,0 +1,762 @@
+// 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 strings implements simple functions to manipulate strings.
+package strings
+
+import (
+ "unicode"
+ "unicode/utf8"
+)
+
+// explode splits s into an array of UTF-8 sequences, one per Unicode character (still strings) up to a maximum of n (n < 0 means no limit).
+// Invalid UTF-8 sequences become correct encodings of U+FFF8.
+func explode(s string, n int) []string {
+ if n == 0 {
+ return nil
+ }
+ l := utf8.RuneCountInString(s)
+ if n <= 0 || n > l {
+ n = l
+ }
+ a := make([]string, n)
+ var size int
+ var ch rune
+ i, cur := 0, 0
+ for ; i+1 < n; i++ {
+ ch, size = utf8.DecodeRuneInString(s[cur:])
+ if ch == utf8.RuneError {
+ a[i] = string(utf8.RuneError)
+ } else {
+ a[i] = s[cur : cur+size]
+ }
+ cur += size
+ }
+ // add the rest, if there is any
+ if cur < len(s) {
+ a[i] = s[cur:]
+ }
+ return a
+}
+
+// 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 string) (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 string) (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
+}
+
+// Count counts the number of non-overlapping instances of sep in s.
+func Count(s, sep string) int {
+ n := 0
+ // special cases
+ switch {
+ case len(sep) == 0:
+ return utf8.RuneCountInString(s) + 1
+ case len(sep) == 1:
+ // special case worth making fast
+ c := sep[0]
+ for i := 0; i < len(s); i++ {
+ if s[i] == c {
+ n++
+ }
+ }
+ return n
+ case len(sep) > len(s):
+ return 0
+ case len(sep) == len(s):
+ if sep == s {
+ return 1
+ }
+ return 0
+ }
+ // Rabin-Karp search
+ hashsep, pow := hashStr(sep)
+ h := uint32(0)
+ for i := 0; i < len(sep); i++ {
+ h = h*primeRK + uint32(s[i])
+ }
+ lastmatch := 0
+ if h == hashsep && s[:len(sep)] == sep {
+ n++
+ lastmatch = len(sep)
+ }
+ for i := len(sep); i < len(s); {
+ h *= primeRK
+ h += uint32(s[i])
+ h -= pow * uint32(s[i-len(sep)])
+ i++
+ if h == hashsep && lastmatch <= i-len(sep) && s[i-len(sep):i] == sep {
+ n++
+ lastmatch = i
+ }
+ }
+ return n
+}
+
+// Contains returns true if substr is within s.
+func Contains(s, substr string) bool {
+ return Index(s, substr) >= 0
+}
+
+// ContainsAny returns true if any Unicode code points in chars are within s.
+func ContainsAny(s, chars string) bool {
+ return IndexAny(s, chars) >= 0
+}
+
+// ContainsRune returns true if the Unicode code point r is within s.
+func ContainsRune(s string, r rune) bool {
+ return IndexRune(s, r) >= 0
+}
+
+// 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 string) int {
+ n := len(sep)
+ switch {
+ case n == 0:
+ return 0
+ case n == 1:
+ return IndexByte(s, sep[0])
+ case n == len(s):
+ if sep == s {
+ return 0
+ }
+ return -1
+ case n > len(s):
+ return -1
+ }
+ // Rabin-Karp search
+ hashsep, pow := hashStr(sep)
+ var h uint32
+ for i := 0; i < n; i++ {
+ h = h*primeRK + uint32(s[i])
+ }
+ if h == hashsep && 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 && s[i-n:i] == sep {
+ return i - n
+ }
+ }
+ 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 string) int {
+ n := len(sep)
+ switch {
+ case n == 0:
+ return len(s)
+ case n == 1:
+ // special case worth making fast
+ c := sep[0]
+ for i := len(s) - 1; i >= 0; i-- {
+ if s[i] == c {
+ return i
+ }
+ }
+ return -1
+ case n == len(s):
+ if sep == s {
+ return 0
+ }
+ return -1
+ case n > len(s):
+ return -1
+ }
+ // Rabin-Karp search from the end of the string
+ hashsep, 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 == hashsep && 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 == hashsep && s[i:i+n] == sep {
+ return i
+ }
+ }
+ return -1
+}
+
+// IndexRune returns the index of the first instance of the Unicode code point
+// r, or -1 if rune is not present in s.
+func IndexRune(s string, r rune) int {
+ switch {
+ case r < utf8.RuneSelf:
+ return IndexByte(s, byte(r))
+ default:
+ for i, c := range s {
+ if c == r {
+ return i
+ }
+ }
+ }
+ return -1
+}
+
+// IndexAny returns the index of the first instance of any Unicode code point
+// from chars in s, or -1 if no Unicode code point from chars is present in s.
+func IndexAny(s, chars string) int {
+ if len(chars) > 0 {
+ for i, c := range s {
+ for _, m := range chars {
+ if c == m {
+ return i
+ }
+ }
+ }
+ }
+ return -1
+}
+
+// LastIndexAny returns the index of the last instance of any Unicode code
+// point from chars in s, or -1 if no Unicode code point from chars is
+// present in s.
+func LastIndexAny(s, chars string) int {
+ if len(chars) > 0 {
+ for i := len(s); i > 0; {
+ rune, size := utf8.DecodeLastRuneInString(s[0:i])
+ i -= size
+ for _, m := range chars {
+ if rune == m {
+ return i
+ }
+ }
+ }
+ }
+ return -1
+}
+
+// Generic split: splits after each instance of sep,
+// including sepSave bytes of sep in the subarrays.
+func genSplit(s, sep string, sepSave, n int) []string {
+ if n == 0 {
+ return nil
+ }
+ if sep == "" {
+ return explode(s, n)
+ }
+ if n < 0 {
+ n = Count(s, sep) + 1
+ }
+ c := sep[0]
+ start := 0
+ a := make([]string, n)
+ na := 0
+ for i := 0; i+len(sep) <= len(s) && na+1 < n; i++ {
+ if s[i] == c && (len(sep) == 1 || 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 substrings separated by sep and returns a slice of
+// the substrings between those separators.
+// If sep is empty, SplitN splits after each UTF-8 sequence.
+// The count determines the number of substrings to return:
+// n > 0: at most n substrings; the last substring will be the unsplit remainder.
+// n == 0: the result is nil (zero substrings)
+// n < 0: all substrings
+func SplitN(s, sep string, n int) []string { return genSplit(s, sep, 0, n) }
+
+// SplitAfterN slices s into substrings after each instance of sep and
+// returns a slice of those substrings.
+// If sep is empty, SplitAfterN splits after each UTF-8 sequence.
+// The count determines the number of substrings to return:
+// n > 0: at most n substrings; the last substring will be the unsplit remainder.
+// n == 0: the result is nil (zero substrings)
+// n < 0: all substrings
+func SplitAfterN(s, sep string, n int) []string {
+ return genSplit(s, sep, len(sep), n)
+}
+
+// Split slices s into all substrings separated by sep and returns a slice of
+// the substrings 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 string) []string { return genSplit(s, sep, 0, -1) }
+
+// SplitAfter slices s into all substrings after each instance of sep and
+// returns a slice of those substrings.
+// 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 string) []string {
+ return genSplit(s, sep, len(sep), -1)
+}
+
+// Fields splits the string s around each instance of one or more consecutive white space
+// characters, as defined by unicode.IsSpace, returning an array of substrings of s or an
+// empty list if s contains only white space.
+func Fields(s string) []string {
+ return FieldsFunc(s, unicode.IsSpace)
+}
+
+// FieldsFunc splits the string s at each run of Unicode code points c satisfying f(c)
+// and returns an array of slices of s. If all code points in s satisfy f(c) or the
+// string is empty, 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 string, f func(rune) bool) []string {
+ // First count the fields.
+ n := 0
+ inField := false
+ for _, rune := range s {
+ wasInField := inField
+ inField = !f(rune)
+ if inField && !wasInField {
+ n++
+ }
+ }
+
+ // Now create them.
+ a := make([]string, n)
+ na := 0
+ fieldStart := -1 // Set to -1 when looking for start of field.
+ for i, rune := range s {
+ if f(rune) {
+ if fieldStart >= 0 {
+ a[na] = s[fieldStart:i]
+ na++
+ fieldStart = -1
+ }
+ } else if fieldStart == -1 {
+ fieldStart = i
+ }
+ }
+ if fieldStart >= 0 { // Last field might end at EOF.
+ a[na] = s[fieldStart:]
+ }
+ return a
+}
+
+// Join concatenates the elements of a to create a single string. The separator string
+// sep is placed between elements in the resulting string.
+func Join(a []string, sep string) string {
+ if len(a) == 0 {
+ return ""
+ }
+ if len(a) == 1 {
+ return a[0]
+ }
+ n := len(sep) * (len(a) - 1)
+ for i := 0; i < len(a); i++ {
+ n += len(a[i])
+ }
+
+ b := make([]byte, n)
+ bp := copy(b, a[0])
+ for _, s := range a[1:] {
+ bp += copy(b[bp:], sep)
+ bp += copy(b[bp:], s)
+ }
+ return string(b)
+}
+
+// HasPrefix tests whether the string s begins with prefix.
+func HasPrefix(s, prefix string) bool {
+ return len(s) >= len(prefix) && s[0:len(prefix)] == prefix
+}
+
+// HasSuffix tests whether the string s ends with suffix.
+func HasSuffix(s, suffix string) bool {
+ return len(s) >= len(suffix) && s[len(s)-len(suffix):] == suffix
+}
+
+// Map returns a copy of the string 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.
+func Map(mapping func(rune) rune, s string) string {
+ // In the worst case, the string 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
+ // The output buffer b is initialized on demand, the first
+ // time a character differs.
+ var b []byte
+
+ for i, c := range s {
+ r := mapping(c)
+ if b == nil {
+ if r == c {
+ continue
+ }
+ b = make([]byte, maxbytes)
+ nbytes = copy(b, s[:i])
+ }
+ if r >= 0 {
+ wid := 1
+ if r >= utf8.RuneSelf {
+ wid = utf8.RuneLen(r)
+ }
+ if nbytes+wid > 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)
+ }
+ }
+ if b == nil {
+ return s
+ }
+ return string(b[0:nbytes])
+}
+
+// Repeat returns a new string consisting of count copies of the string s.
+func Repeat(s string, count int) string {
+ b := make([]byte, len(s)*count)
+ bp := copy(b, s)
+ for bp < len(b) {
+ copy(b[bp:], b[:bp])
+ bp *= 2
+ }
+ return string(b)
+}
+
+// ToUpper returns a copy of the string s with all Unicode letters mapped to their upper case.
+func ToUpper(s string) string { return Map(unicode.ToUpper, s) }
+
+// ToLower returns a copy of the string s with all Unicode letters mapped to their lower case.
+func ToLower(s string) string { return Map(unicode.ToLower, s) }
+
+// ToTitle returns a copy of the string s with all Unicode letters mapped to their title case.
+func ToTitle(s string) string { return Map(unicode.ToTitle, s) }
+
+// ToUpperSpecial returns a copy of the string s with all Unicode letters mapped to their
+// upper case, giving priority to the special casing rules.
+func ToUpperSpecial(_case unicode.SpecialCase, s string) string {
+ return Map(func(r rune) rune { return _case.ToUpper(r) }, s)
+}
+
+// ToLowerSpecial returns a copy of the string s with all Unicode letters mapped to their
+// lower case, giving priority to the special casing rules.
+func ToLowerSpecial(_case unicode.SpecialCase, s string) string {
+ return Map(func(r rune) rune { return _case.ToLower(r) }, s)
+}
+
+// ToTitleSpecial returns a copy of the string s with all Unicode letters mapped to their
+// title case, giving priority to the special casing rules.
+func ToTitleSpecial(_case unicode.SpecialCase, s string) string {
+ 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 the string s with all Unicode letters that begin words
+// mapped to their title case.
+//
+// BUG: The rule Title uses for word boundaries does not handle Unicode punctuation properly.
+func Title(s string) string {
+ // 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 slice of the string s with all leading
+// Unicode code points c satisfying f(c) removed.
+func TrimLeftFunc(s string, f func(rune) bool) string {
+ i := indexFunc(s, f, false)
+ if i == -1 {
+ return ""
+ }
+ return s[i:]
+}
+
+// TrimRightFunc returns a slice of the string s with all trailing
+// Unicode code points c satisfying f(c) removed.
+func TrimRightFunc(s string, f func(rune) bool) string {
+ i := lastIndexFunc(s, f, false)
+ if i >= 0 && s[i] >= utf8.RuneSelf {
+ _, wid := utf8.DecodeRuneInString(s[i:])
+ i += wid
+ } else {
+ i++
+ }
+ return s[0:i]
+}
+
+// TrimFunc returns a slice of the string s with all leading
+// and trailing Unicode code points c satisfying f(c) removed.
+func TrimFunc(s string, f func(rune) bool) string {
+ return TrimRightFunc(TrimLeftFunc(s, f), f)
+}
+
+// IndexFunc returns the index into s of the first Unicode
+// code point satisfying f(c), or -1 if none do.
+func IndexFunc(s string, f func(rune) bool) int {
+ return indexFunc(s, f, true)
+}
+
+// LastIndexFunc returns the index into s of the last
+// Unicode code point satisfying f(c), or -1 if none do.
+func LastIndexFunc(s string, f func(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 string, f func(rune) bool, truth bool) int {
+ start := 0
+ for start < len(s) {
+ wid := 1
+ r := rune(s[start])
+ if r >= utf8.RuneSelf {
+ r, wid = utf8.DecodeRuneInString(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 string, f func(rune) bool, truth bool) int {
+ for i := len(s); i > 0; {
+ r, size := utf8.DecodeLastRuneInString(s[0:i])
+ i -= size
+ if f(r) == truth {
+ return i
+ }
+ }
+ return -1
+}
+
+func makeCutsetFunc(cutset string) func(rune) bool {
+ return func(r rune) bool { return IndexRune(cutset, r) >= 0 }
+}
+
+// Trim returns a slice of the string s with all leading and
+// trailing Unicode code points contained in cutset removed.
+func Trim(s string, cutset string) string {
+ if s == "" || cutset == "" {
+ return s
+ }
+ return TrimFunc(s, makeCutsetFunc(cutset))
+}
+
+// TrimLeft returns a slice of the string s with all leading
+// Unicode code points contained in cutset removed.
+func TrimLeft(s string, cutset string) string {
+ if s == "" || cutset == "" {
+ return s
+ }
+ return TrimLeftFunc(s, makeCutsetFunc(cutset))
+}
+
+// TrimRight returns a slice of the string s, with all trailing
+// Unicode code points contained in cutset removed.
+func TrimRight(s string, cutset string) string {
+ if s == "" || cutset == "" {
+ return s
+ }
+ return TrimRightFunc(s, makeCutsetFunc(cutset))
+}
+
+// TrimSpace returns a slice of the string s, with all leading
+// and trailing white space removed, as defined by Unicode.
+func TrimSpace(s string) string {
+ return TrimFunc(s, unicode.IsSpace)
+}
+
+// TrimPrefix returns s without the provided leading prefix string.
+// If s doesn't start with prefix, s is returned unchanged.
+func TrimPrefix(s, prefix string) string {
+ 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 string) string {
+ if HasSuffix(s, suffix) {
+ return s[:len(s)-len(suffix)]
+ }
+ return s
+}
+
+// Replace returns a copy of the string s with the first n
+// non-overlapping instances of old replaced by new.
+// If old is empty, it matches at the beginning of the string
+// and after each UTF-8 sequence, yielding up to k+1 replacements
+// for a k-rune string.
+// If n < 0, there is no limit on the number of replacements.
+func Replace(s, old, new string, n int) string {
+ if old == new || n == 0 {
+ return s // avoid allocation
+ }
+
+ // Compute number of replacements.
+ if m := Count(s, old); m == 0 {
+ return s // avoid allocation
+ } else 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.DecodeRuneInString(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 string(t[0:w])
+}
+
+// EqualFold reports whether s and t, interpreted as UTF-8 strings,
+// are equal under Unicode case-folding.
+func EqualFold(s, t string) bool {
+ for s != "" && t != "" {
+ // Extract first rune from each string.
+ var sr, tr rune
+ if s[0] < utf8.RuneSelf {
+ sr, s = rune(s[0]), s[1:]
+ } else {
+ r, size := utf8.DecodeRuneInString(s)
+ sr, s = r, s[size:]
+ }
+ if t[0] < utf8.RuneSelf {
+ tr, t = rune(t[0]), t[1:]
+ } else {
+ r, size := utf8.DecodeRuneInString(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 s == t
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-06-14 01:10:22 +0000