Ydb stable 22-4-4322.4.43

x-stable-origin-commit: 8d49d46cc834835bf3e50870516acd7376a63bcf

7 files changed, 2220 insertions, 0 deletions

diff --git a/contrib/go/_std_1.18/src/strings/builder.go b/contrib/go/_std_1.18/src/strings/builder.go
new file mode 100644
index 0000000000..ba4df618bf
--- /dev/null
+++ b/contrib/go/_std_1.18/src/strings/builder.go
@@ -0,0 +1,125 @@
+// Copyright 2017 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
+
+import (
+	"unicode/utf8"
+	"unsafe"
+)
+
+// A Builder is used to efficiently build a string using Write methods.
+// It minimizes memory copying. The zero value is ready to use.
+// Do not copy a non-zero Builder.
+type Builder struct {
+	addr *Builder // of receiver, to detect copies by value
+	buf  []byte
+}
+
+// noescape hides a pointer from escape analysis. It is the identity function
+// but escape analysis doesn't think the output depends on the input.
+// noescape is inlined and currently compiles down to zero instructions.
+// USE CAREFULLY!
+// This was copied from the runtime; see issues 23382 and 7921.
+//go:nosplit
+//go:nocheckptr
+func noescape(p unsafe.Pointer) unsafe.Pointer {
+	x := uintptr(p)
+	return unsafe.Pointer(x ^ 0)
+}
+
+func (b *Builder) copyCheck() {
+	if b.addr == nil {
+		// This hack works around a failing of Go's escape analysis
+		// that was causing b to escape and be heap allocated.
+		// See issue 23382.
+		// TODO: once issue 7921 is fixed, this should be reverted to
+		// just "b.addr = b".
+		b.addr = (*Builder)(noescape(unsafe.Pointer(b)))
+	} else if b.addr != b {
+		panic("strings: illegal use of non-zero Builder copied by value")
+	}
+}
+
+// String returns the accumulated string.
+func (b *Builder) String() string {
+	return *(*string)(unsafe.Pointer(&b.buf))
+}
+
+// Len returns the number of accumulated bytes; b.Len() == len(b.String()).
+func (b *Builder) Len() int { return len(b.buf) }
+
+// Cap returns the capacity of the builder's underlying byte slice. It is the
+// total space allocated for the string being built and includes any bytes
+// already written.
+func (b *Builder) Cap() int { return cap(b.buf) }
+
+// Reset resets the Builder to be empty.
+func (b *Builder) Reset() {
+	b.addr = nil
+	b.buf = nil
+}
+
+// grow copies the buffer to a new, larger buffer so that there are at least n
+// bytes of capacity beyond len(b.buf).
+func (b *Builder) grow(n int) {
+	buf := make([]byte, len(b.buf), 2*cap(b.buf)+n)
+	copy(buf, b.buf)
+	b.buf = buf
+}
+
+// Grow grows b's capacity, if necessary, to guarantee space for
+// another n bytes. After Grow(n), at least n bytes can be written to b
+// without another allocation. If n is negative, Grow panics.
+func (b *Builder) Grow(n int) {
+	b.copyCheck()
+	if n < 0 {
+		panic("strings.Builder.Grow: negative count")
+	}
+	if cap(b.buf)-len(b.buf) < n {
+		b.grow(n)
+	}
+}
+
+// Write appends the contents of p to b's buffer.
+// Write always returns len(p), nil.
+func (b *Builder) Write(p []byte) (int, error) {
+	b.copyCheck()
+	b.buf = append(b.buf, p...)
+	return len(p), nil
+}
+
+// WriteByte appends the byte c to b's buffer.
+// The returned error is always nil.
+func (b *Builder) WriteByte(c byte) error {
+	b.copyCheck()
+	b.buf = append(b.buf, c)
+	return nil
+}
+
+// WriteRune appends the UTF-8 encoding of Unicode code point r to b's buffer.
+// It returns the length of r and a nil error.
+func (b *Builder) WriteRune(r rune) (int, error) {
+	b.copyCheck()
+	// Compare as uint32 to correctly handle negative runes.
+	if uint32(r) < utf8.RuneSelf {
+		b.buf = append(b.buf, byte(r))
+		return 1, nil
+	}
+	l := len(b.buf)
+	if cap(b.buf)-l < utf8.UTFMax {
+		b.grow(utf8.UTFMax)
+	}
+	n := utf8.EncodeRune(b.buf[l:l+utf8.UTFMax], r)
+	b.buf = b.buf[:l+n]
+	return n, nil
+}
+
+// WriteString appends the contents of s to b's buffer.
+// It returns the length of s and a nil error.
+func (b *Builder) WriteString(s string) (int, error) {
+	b.copyCheck()
+	b.buf = append(b.buf, s...)
+	return len(s), nil
+}
diff --git a/contrib/go/_std_1.18/src/strings/clone.go b/contrib/go/_std_1.18/src/strings/clone.go
new file mode 100644
index 0000000000..edd1497d9e
--- /dev/null
+++ b/contrib/go/_std_1.18/src/strings/clone.go
@@ -0,0 +1,28 @@
+// Copyright 2021 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
+
+import (
+	"unsafe"
+)
+
+// Clone returns a fresh copy of s.
+// It guarantees to make a copy of s into a new allocation,
+// which can be important when retaining only a small substring
+// of a much larger string. Using Clone can help such programs
+// use less memory. Of course, since using Clone makes a copy,
+// overuse of Clone can make programs use more memory.
+// Clone should typically be used only rarely, and only when
+// profiling indicates that it is needed.
+// For strings of length zero the string "" will be returned
+// and no allocation is made.
+func Clone(s string) string {
+	if len(s) == 0 {
+		return ""
+	}
+	b := make([]byte, len(s))
+	copy(b, s)
+	return *(*string)(unsafe.Pointer(&b))
+}
diff --git a/contrib/go/_std_1.18/src/strings/compare.go b/contrib/go/_std_1.18/src/strings/compare.go
new file mode 100644
index 0000000000..2bd4a243db
--- /dev/null
+++ b/contrib/go/_std_1.18/src/strings/compare.go
@@ -0,0 +1,28 @@
+// Copyright 2015 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
+
+// Compare returns an integer comparing two strings lexicographically.
+// The result will be 0 if a == b, -1 if a < b, and +1 if a > b.
+//
+// Compare is included only for symmetry with package bytes.
+// It is usually clearer and always faster to use the built-in
+// string comparison operators ==, <, >, and so on.
+func Compare(a, b string) int {
+	// NOTE(rsc): This function does NOT call the runtime cmpstring function,
+	// because we do not want to provide any performance justification for
+	// using strings.Compare. Basically no one should use strings.Compare.
+	// As the comment above says, it is here only for symmetry with package bytes.
+	// If performance is important, the compiler should be changed to recognize
+	// the pattern so that all code doing three-way comparisons, not just code
+	// using strings.Compare, can benefit.
+	if a == b {
+		return 0
+	}
+	if a < b {
+		return -1
+	}
+	return +1
+}
diff --git a/contrib/go/_std_1.18/src/strings/reader.go b/contrib/go/_std_1.18/src/strings/reader.go
new file mode 100644
index 0000000000..6f069a62ca
--- /dev/null
+++ b/contrib/go/_std_1.18/src/strings/reader.go
@@ -0,0 +1,160 @@
+// 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
+
+import (
+	"errors"
+	"io"
+	"unicode/utf8"
+)
+
+// A Reader implements the io.Reader, io.ReaderAt, io.ByteReader, io.ByteScanner,
+// io.RuneReader, io.RuneScanner, io.Seeker, and io.WriterTo interfaces by reading
+// from a string.
+// The zero value for Reader operates like a Reader of an empty string.
+type Reader struct {
+	s        string
+	i        int64 // current reading index
+	prevRune int   // index of previous rune; or < 0
+}
+
+// Len returns the number of bytes of the unread portion of the
+// string.
+func (r *Reader) Len() int {
+	if r.i >= int64(len(r.s)) {
+		return 0
+	}
+	return int(int64(len(r.s)) - r.i)
+}
+
+// Size returns the original length of the underlying string.
+// Size is the number of bytes available for reading via ReadAt.
+// The returned value is always the same and is not affected by calls
+// to any other method.
+func (r *Reader) Size() int64 { return int64(len(r.s)) }
+
+// Read implements the io.Reader interface.
+func (r *Reader) Read(b []byte) (n int, err error) {
+	if r.i >= int64(len(r.s)) {
+		return 0, io.EOF
+	}
+	r.prevRune = -1
+	n = copy(b, r.s[r.i:])
+	r.i += int64(n)
+	return
+}
+
+// ReadAt implements the io.ReaderAt interface.
+func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
+	// cannot modify state - see io.ReaderAt
+	if off < 0 {
+		return 0, errors.New("strings.Reader.ReadAt: negative offset")
+	}
+	if off >= int64(len(r.s)) {
+		return 0, io.EOF
+	}
+	n = copy(b, r.s[off:])
+	if n < len(b) {
+		err = io.EOF
+	}
+	return
+}
+
+// ReadByte implements the io.ByteReader interface.
+func (r *Reader) ReadByte() (byte, error) {
+	r.prevRune = -1
+	if r.i >= int64(len(r.s)) {
+		return 0, io.EOF
+	}
+	b := r.s[r.i]
+	r.i++
+	return b, nil
+}
+
+// UnreadByte implements the io.ByteScanner interface.
+func (r *Reader) UnreadByte() error {
+	if r.i <= 0 {
+		return errors.New("strings.Reader.UnreadByte: at beginning of string")
+	}
+	r.prevRune = -1
+	r.i--
+	return nil
+}
+
+// ReadRune implements the io.RuneReader interface.
+func (r *Reader) ReadRune() (ch rune, size int, err error) {
+	if r.i >= int64(len(r.s)) {
+		r.prevRune = -1
+		return 0, 0, io.EOF
+	}
+	r.prevRune = int(r.i)
+	if c := r.s[r.i]; c < utf8.RuneSelf {
+		r.i++
+		return rune(c), 1, nil
+	}
+	ch, size = utf8.DecodeRuneInString(r.s[r.i:])
+	r.i += int64(size)
+	return
+}
+
+// UnreadRune implements the io.RuneScanner interface.
+func (r *Reader) UnreadRune() error {
+	if r.i <= 0 {
+		return errors.New("strings.Reader.UnreadRune: at beginning of string")
+	}
+	if r.prevRune < 0 {
+		return errors.New("strings.Reader.UnreadRune: previous operation was not ReadRune")
+	}
+	r.i = int64(r.prevRune)
+	r.prevRune = -1
+	return nil
+}
+
+// Seek implements the io.Seeker interface.
+func (r *Reader) Seek(offset int64, whence int) (int64, error) {
+	r.prevRune = -1
+	var abs int64
+	switch whence {
+	case io.SeekStart:
+		abs = offset
+	case io.SeekCurrent:
+		abs = r.i + offset
+	case io.SeekEnd:
+		abs = int64(len(r.s)) + offset
+	default:
+		return 0, errors.New("strings.Reader.Seek: invalid whence")
+	}
+	if abs < 0 {
+		return 0, errors.New("strings.Reader.Seek: negative position")
+	}
+	r.i = abs
+	return abs, nil
+}
+
+// WriteTo implements the io.WriterTo interface.
+func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
+	r.prevRune = -1
+	if r.i >= int64(len(r.s)) {
+		return 0, nil
+	}
+	s := r.s[r.i:]
+	m, err := io.WriteString(w, s)
+	if m > len(s) {
+		panic("strings.Reader.WriteTo: invalid WriteString count")
+	}
+	r.i += int64(m)
+	n = int64(m)
+	if m != len(s) && err == nil {
+		err = io.ErrShortWrite
+	}
+	return
+}
+
+// Reset resets the Reader to be reading from s.
+func (r *Reader) Reset(s string) { *r = Reader{s, 0, -1} }
+
+// NewReader returns a new Reader reading from s.
+// It is similar to bytes.NewBufferString but more efficient and read-only.
+func NewReader(s string) *Reader { return &Reader{s, 0, -1} }
diff --git a/contrib/go/_std_1.18/src/strings/replace.go b/contrib/go/_std_1.18/src/strings/replace.go
new file mode 100644
index 0000000000..ee728bb22b
--- /dev/null
+++ b/contrib/go/_std_1.18/src/strings/replace.go
@@ -0,0 +1,569 @@
+// Copyright 2011 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
+
+import (
+	"io"
+	"sync"
+)
+
+// Replacer replaces a list of strings with replacements.
+// It is safe for concurrent use by multiple goroutines.
+type Replacer struct {
+	once   sync.Once // guards buildOnce method
+	r      replacer
+	oldnew []string
+}
+
+// replacer is the interface that a replacement algorithm needs to implement.
+type replacer interface {
+	Replace(s string) string
+	WriteString(w io.Writer, s string) (n int, err error)
+}
+
+// NewReplacer returns a new Replacer from a list of old, new string
+// pairs. Replacements are performed in the order they appear in the
+// target string, without overlapping matches. The old string
+// comparisons are done in argument order.
+//
+// NewReplacer panics if given an odd number of arguments.
+func NewReplacer(oldnew ...string) *Replacer {
+	if len(oldnew)%2 == 1 {
+		panic("strings.NewReplacer: odd argument count")
+	}
+	return &Replacer{oldnew: append([]string(nil), oldnew...)}
+}
+
+func (r *Replacer) buildOnce() {
+	r.r = r.build()
+	r.oldnew = nil
+}
+
+func (b *Replacer) build() replacer {
+	oldnew := b.oldnew
+	if len(oldnew) == 2 && len(oldnew[0]) > 1 {
+		return makeSingleStringReplacer(oldnew[0], oldnew[1])
+	}
+
+	allNewBytes := true
+	for i := 0; i < len(oldnew); i += 2 {
+		if len(oldnew[i]) != 1 {
+			return makeGenericReplacer(oldnew)
+		}
+		if len(oldnew[i+1]) != 1 {
+			allNewBytes = false
+		}
+	}
+
+	if allNewBytes {
+		r := byteReplacer{}
+		for i := range r {
+			r[i] = byte(i)
+		}
+		// The first occurrence of old->new map takes precedence
+		// over the others with the same old string.
+		for i := len(oldnew) - 2; i >= 0; i -= 2 {
+			o := oldnew[i][0]
+			n := oldnew[i+1][0]
+			r[o] = n
+		}
+		return &r
+	}
+
+	r := byteStringReplacer{toReplace: make([]string, 0, len(oldnew)/2)}
+	// The first occurrence of old->new map takes precedence
+	// over the others with the same old string.
+	for i := len(oldnew) - 2; i >= 0; i -= 2 {
+		o := oldnew[i][0]
+		n := oldnew[i+1]
+		// To avoid counting repetitions multiple times.
+		if r.replacements[o] == nil {
+			// We need to use string([]byte{o}) instead of string(o),
+			// to avoid utf8 encoding of o.
+			// E. g. byte(150) produces string of length 2.
+			r.toReplace = append(r.toReplace, string([]byte{o}))
+		}
+		r.replacements[o] = []byte(n)
+
+	}
+	return &r
+}
+
+// Replace returns a copy of s with all replacements performed.
+func (r *Replacer) Replace(s string) string {
+	r.once.Do(r.buildOnce)
+	return r.r.Replace(s)
+}
+
+// WriteString writes s to w with all replacements performed.
+func (r *Replacer) WriteString(w io.Writer, s string) (n int, err error) {
+	r.once.Do(r.buildOnce)
+	return r.r.WriteString(w, s)
+}
+
+// trieNode is a node in a lookup trie for prioritized key/value pairs. Keys
+// and values may be empty. For example, the trie containing keys "ax", "ay",
+// "bcbc", "x" and "xy" could have eight nodes:
+//
+//  n0  -
+//  n1  a-
+//  n2  .x+
+//  n3  .y+
+//  n4  b-
+//  n5  .cbc+
+//  n6  x+
+//  n7  .y+
+//
+// n0 is the root node, and its children are n1, n4 and n6; n1's children are
+// n2 and n3; n4's child is n5; n6's child is n7. Nodes n0, n1 and n4 (marked
+// with a trailing "-") are partial keys, and nodes n2, n3, n5, n6 and n7
+// (marked with a trailing "+") are complete keys.
+type trieNode struct {
+	// value is the value of the trie node's key/value pair. It is empty if
+	// this node is not a complete key.
+	value string
+	// priority is the priority (higher is more important) of the trie node's
+	// key/value pair; keys are not necessarily matched shortest- or longest-
+	// first. Priority is positive if this node is a complete key, and zero
+	// otherwise. In the example above, positive/zero priorities are marked
+	// with a trailing "+" or "-".
+	priority int
+
+	// A trie node may have zero, one or more child nodes:
+	//  * if the remaining fields are zero, there are no children.
+	//  * if prefix and next are non-zero, there is one child in next.
+	//  * if table is non-zero, it defines all the children.
+	//
+	// Prefixes are preferred over tables when there is one child, but the
+	// root node always uses a table for lookup efficiency.
+
+	// prefix is the difference in keys between this trie node and the next.
+	// In the example above, node n4 has prefix "cbc" and n4's next node is n5.
+	// Node n5 has no children and so has zero prefix, next and table fields.
+	prefix string
+	next   *trieNode
+
+	// table is a lookup table indexed by the next byte in the key, after
+	// remapping that byte through genericReplacer.mapping to create a dense
+	// index. In the example above, the keys only use 'a', 'b', 'c', 'x' and
+	// 'y', which remap to 0, 1, 2, 3 and 4. All other bytes remap to 5, and
+	// genericReplacer.tableSize will be 5. Node n0's table will be
+	// []*trieNode{ 0:n1, 1:n4, 3:n6 }, where the 0, 1 and 3 are the remapped
+	// 'a', 'b' and 'x'.
+	table []*trieNode
+}
+
+func (t *trieNode) add(key, val string, priority int, r *genericReplacer) {
+	if key == "" {
+		if t.priority == 0 {
+			t.value = val
+			t.priority = priority
+		}
+		return
+	}
+
+	if t.prefix != "" {
+		// Need to split the prefix among multiple nodes.
+		var n int // length of the longest common prefix
+		for ; n < len(t.prefix) && n < len(key); n++ {
+			if t.prefix[n] != key[n] {
+				break
+			}
+		}
+		if n == len(t.prefix) {
+			t.next.add(key[n:], val, priority, r)
+		} else if n == 0 {
+			// First byte differs, start a new lookup table here. Looking up
+			// what is currently t.prefix[0] will lead to prefixNode, and
+			// looking up key[0] will lead to keyNode.
+			var prefixNode *trieNode
+			if len(t.prefix) == 1 {
+				prefixNode = t.next
+			} else {
+				prefixNode = &trieNode{
+					prefix: t.prefix[1:],
+					next:   t.next,
+				}
+			}
+			keyNode := new(trieNode)
+			t.table = make([]*trieNode, r.tableSize)
+			t.table[r.mapping[t.prefix[0]]] = prefixNode
+			t.table[r.mapping[key[0]]] = keyNode
+			t.prefix = ""
+			t.next = nil
+			keyNode.add(key[1:], val, priority, r)
+		} else {
+			// Insert new node after the common section of the prefix.
+			next := &trieNode{
+				prefix: t.prefix[n:],
+				next:   t.next,
+			}
+			t.prefix = t.prefix[:n]
+			t.next = next
+			next.add(key[n:], val, priority, r)
+		}
+	} else if t.table != nil {
+		// Insert into existing table.
+		m := r.mapping[key[0]]
+		if t.table[m] == nil {
+			t.table[m] = new(trieNode)
+		}
+		t.table[m].add(key[1:], val, priority, r)
+	} else {
+		t.prefix = key
+		t.next = new(trieNode)
+		t.next.add("", val, priority, r)
+	}
+}
+
+func (r *genericReplacer) lookup(s string, ignoreRoot bool) (val string, keylen int, found bool) {
+	// Iterate down the trie to the end, and grab the value and keylen with
+	// the highest priority.
+	bestPriority := 0
+	node := &r.root
+	n := 0
+	for node != nil {
+		if node.priority > bestPriority && !(ignoreRoot && node == &r.root) {
+			bestPriority = node.priority
+			val = node.value
+			keylen = n
+			found = true
+		}
+
+		if s == "" {
+			break
+		}
+		if node.table != nil {
+			index := r.mapping[s[0]]
+			if int(index) == r.tableSize {
+				break
+			}
+			node = node.table[index]
+			s = s[1:]
+			n++
+		} else if node.prefix != "" && HasPrefix(s, node.prefix) {
+			n += len(node.prefix)
+			s = s[len(node.prefix):]
+			node = node.next
+		} else {
+			break
+		}
+	}
+	return
+}
+
+// genericReplacer is the fully generic algorithm.
+// It's used as a fallback when nothing faster can be used.
+type genericReplacer struct {
+	root trieNode
+	// tableSize is the size of a trie node's lookup table. It is the number
+	// of unique key bytes.
+	tableSize int
+	// mapping maps from key bytes to a dense index for trieNode.table.
+	mapping [256]byte
+}
+
+func makeGenericReplacer(oldnew []string) *genericReplacer {
+	r := new(genericReplacer)
+	// Find each byte used, then assign them each an index.
+	for i := 0; i < len(oldnew); i += 2 {
+		key := oldnew[i]
+		for j := 0; j < len(key); j++ {
+			r.mapping[key[j]] = 1
+		}
+	}
+
+	for _, b := range r.mapping {
+		r.tableSize += int(b)
+	}
+
+	var index byte
+	for i, b := range r.mapping {
+		if b == 0 {
+			r.mapping[i] = byte(r.tableSize)
+		} else {
+			r.mapping[i] = index
+			index++
+		}
+	}
+	// Ensure root node uses a lookup table (for performance).
+	r.root.table = make([]*trieNode, r.tableSize)
+
+	for i := 0; i < len(oldnew); i += 2 {
+		r.root.add(oldnew[i], oldnew[i+1], len(oldnew)-i, r)
+	}
+	return r
+}
+
+type appendSliceWriter []byte
+
+// Write writes to the buffer to satisfy io.Writer.
+func (w *appendSliceWriter) Write(p []byte) (int, error) {
+	*w = append(*w, p...)
+	return len(p), nil
+}
+
+// WriteString writes to the buffer without string->[]byte->string allocations.
+func (w *appendSliceWriter) WriteString(s string) (int, error) {
+	*w = append(*w, s...)
+	return len(s), nil
+}
+
+type stringWriter struct {
+	w io.Writer
+}
+
+func (w stringWriter) WriteString(s string) (int, error) {
+	return w.w.Write([]byte(s))
+}
+
+func getStringWriter(w io.Writer) io.StringWriter {
+	sw, ok := w.(io.StringWriter)
+	if !ok {
+		sw = stringWriter{w}
+	}
+	return sw
+}
+
+func (r *genericReplacer) Replace(s string) string {
+	buf := make(appendSliceWriter, 0, len(s))
+	r.WriteString(&buf, s)
+	return string(buf)
+}
+
+func (r *genericReplacer) WriteString(w io.Writer, s string) (n int, err error) {
+	sw := getStringWriter(w)
+	var last, wn int
+	var prevMatchEmpty bool
+	for i := 0; i <= len(s); {
+		// Fast path: s[i] is not a prefix of any pattern.
+		if i != len(s) && r.root.priority == 0 {
+			index := int(r.mapping[s[i]])
+			if index == r.tableSize || r.root.table[index] == nil {
+				i++
+				continue
+			}
+		}
+
+		// Ignore the empty match iff the previous loop found the empty match.
+		val, keylen, match := r.lookup(s[i:], prevMatchEmpty)
+		prevMatchEmpty = match && keylen == 0
+		if match {
+			wn, err = sw.WriteString(s[last:i])
+			n += wn
+			if err != nil {
+				return
+			}
+			wn, err = sw.WriteString(val)
+			n += wn
+			if err != nil {
+				return
+			}
+			i += keylen
+			last = i
+			continue
+		}
+		i++
+	}
+	if last != len(s) {
+		wn, err = sw.WriteString(s[last:])
+		n += wn
+	}
+	return
+}
+
+// singleStringReplacer is the implementation that's used when there is only
+// one string to replace (and that string has more than one byte).
+type singleStringReplacer struct {
+	finder *stringFinder
+	// value is the new string that replaces that pattern when it's found.
+	value string
+}
+
+func makeSingleStringReplacer(pattern string, value string) *singleStringReplacer {
+	return &singleStringReplacer{finder: makeStringFinder(pattern), value: value}
+}
+
+func (r *singleStringReplacer) Replace(s string) string {
+	var buf Builder
+	i, matched := 0, false
+	for {
+		match := r.finder.next(s[i:])
+		if match == -1 {
+			break
+		}
+		matched = true
+		buf.Grow(match + len(r.value))
+		buf.WriteString(s[i : i+match])
+		buf.WriteString(r.value)
+		i += match + len(r.finder.pattern)
+	}
+	if !matched {
+		return s
+	}
+	buf.WriteString(s[i:])
+	return buf.String()
+}
+
+func (r *singleStringReplacer) WriteString(w io.Writer, s string) (n int, err error) {
+	sw := getStringWriter(w)
+	var i, wn int
+	for {
+		match := r.finder.next(s[i:])
+		if match == -1 {
+			break
+		}
+		wn, err = sw.WriteString(s[i : i+match])
+		n += wn
+		if err != nil {
+			return
+		}
+		wn, err = sw.WriteString(r.value)
+		n += wn
+		if err != nil {
+			return
+		}
+		i += match + len(r.finder.pattern)
+	}
+	wn, err = sw.WriteString(s[i:])
+	n += wn
+	return
+}
+
+// byteReplacer is the implementation that's used when all the "old"
+// and "new" values are single ASCII bytes.
+// The array contains replacement bytes indexed by old byte.
+type byteReplacer [256]byte
+
+func (r *byteReplacer) Replace(s string) string {
+	var buf []byte // lazily allocated
+	for i := 0; i < len(s); i++ {
+		b := s[i]
+		if r[b] != b {
+			if buf == nil {
+				buf = []byte(s)
+			}
+			buf[i] = r[b]
+		}
+	}
+	if buf == nil {
+		return s
+	}
+	return string(buf)
+}
+
+func (r *byteReplacer) WriteString(w io.Writer, s string) (n int, err error) {
+	// TODO(bradfitz): use io.WriteString with slices of s, avoiding allocation.
+	bufsize := 32 << 10
+	if len(s) < bufsize {
+		bufsize = len(s)
+	}
+	buf := make([]byte, bufsize)
+
+	for len(s) > 0 {
+		ncopy := copy(buf, s)
+		s = s[ncopy:]
+		for i, b := range buf[:ncopy] {
+			buf[i] = r[b]
+		}
+		wn, err := w.Write(buf[:ncopy])
+		n += wn
+		if err != nil {
+			return n, err
+		}
+	}
+	return n, nil
+}
+
+// byteStringReplacer is the implementation that's used when all the
+// "old" values are single ASCII bytes but the "new" values vary in size.
+type byteStringReplacer struct {
+	// replacements contains replacement byte slices indexed by old byte.
+	// A nil []byte means that the old byte should not be replaced.
+	replacements [256][]byte
+	// toReplace keeps a list of bytes to replace. Depending on length of toReplace
+	// and length of target string it may be faster to use Count, or a plain loop.
+	// We store single byte as a string, because Count takes a string.
+	toReplace []string
+}
+
+// countCutOff controls the ratio of a string length to a number of replacements
+// at which (*byteStringReplacer).Replace switches algorithms.
+// For strings with higher ration of length to replacements than that value,
+// we call Count, for each replacement from toReplace.
+// For strings, with a lower ratio we use simple loop, because of Count overhead.
+// countCutOff is an empirically determined overhead multiplier.
+// TODO(tocarip) revisit once we have register-based abi/mid-stack inlining.
+const countCutOff = 8
+
+func (r *byteStringReplacer) Replace(s string) string {
+	newSize := len(s)
+	anyChanges := false
+	// Is it faster to use Count?
+	if len(r.toReplace)*countCutOff <= len(s) {
+		for _, x := range r.toReplace {
+			if c := Count(s, x); c != 0 {
+				// The -1 is because we are replacing 1 byte with len(replacements[b]) bytes.
+				newSize += c * (len(r.replacements[x[0]]) - 1)
+				anyChanges = true
+			}
+
+		}
+	} else {
+		for i := 0; i < len(s); i++ {
+			b := s[i]
+			if r.replacements[b] != nil {
+				// See above for explanation of -1
+				newSize += len(r.replacements[b]) - 1
+				anyChanges = true
+			}
+		}
+	}
+	if !anyChanges {
+		return s
+	}
+	buf := make([]byte, newSize)
+	j := 0
+	for i := 0; i < len(s); i++ {
+		b := s[i]
+		if r.replacements[b] != nil {
+			j += copy(buf[j:], r.replacements[b])
+		} else {
+			buf[j] = b
+			j++
+		}
+	}
+	return string(buf)
+}
+
+func (r *byteStringReplacer) WriteString(w io.Writer, s string) (n int, err error) {
+	sw := getStringWriter(w)
+	last := 0
+	for i := 0; i < len(s); i++ {
+		b := s[i]
+		if r.replacements[b] == nil {
+			continue
+		}
+		if last != i {
+			nw, err := sw.WriteString(s[last:i])
+			n += nw
+			if err != nil {
+				return n, err
+			}
+		}
+		last = i + 1
+		nw, err := w.Write(r.replacements[b])
+		n += nw
+		if err != nil {
+			return n, err
+		}
+	}
+	if last != len(s) {
+		var nw int
+		nw, err = sw.WriteString(s[last:])
+		n += nw
+	}
+	return
+}
diff --git a/contrib/go/_std_1.18/src/strings/search.go b/contrib/go/_std_1.18/src/strings/search.go
new file mode 100644
index 0000000000..e5bffbbfe8
--- /dev/null
+++ b/contrib/go/_std_1.18/src/strings/search.go
@@ -0,0 +1,124 @@
+// Copyright 2012 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
+
+// stringFinder efficiently finds strings in a source text. It's implemented
+// using the Boyer-Moore string search algorithm:
+// https://en.wikipedia.org/wiki/Boyer-Moore_string_search_algorithm
+// https://www.cs.utexas.edu/~moore/publications/fstrpos.pdf (note: this aged
+// document uses 1-based indexing)
+type stringFinder struct {
+	// pattern is the string that we are searching for in the text.
+	pattern string
+
+	// badCharSkip[b] contains the distance between the last byte of pattern
+	// and the rightmost occurrence of b in pattern. If b is not in pattern,
+	// badCharSkip[b] is len(pattern).
+	//
+	// Whenever a mismatch is found with byte b in the text, we can safely
+	// shift the matching frame at least badCharSkip[b] until the next time
+	// the matching char could be in alignment.
+	badCharSkip [256]int
+
+	// goodSuffixSkip[i] defines how far we can shift the matching frame given
+	// that the suffix pattern[i+1:] matches, but the byte pattern[i] does
+	// not. There are two cases to consider:
+	//
+	// 1. The matched suffix occurs elsewhere in pattern (with a different
+	// byte preceding it that we might possibly match). In this case, we can
+	// shift the matching frame to align with the next suffix chunk. For
+	// example, the pattern "mississi" has the suffix "issi" next occurring
+	// (in right-to-left order) at index 1, so goodSuffixSkip[3] ==
+	// shift+len(suffix) == 3+4 == 7.
+	//
+	// 2. If the matched suffix does not occur elsewhere in pattern, then the
+	// matching frame may share part of its prefix with the end of the
+	// matching suffix. In this case, goodSuffixSkip[i] will contain how far
+	// to shift the frame to align this portion of the prefix to the
+	// suffix. For example, in the pattern "abcxxxabc", when the first
+	// mismatch from the back is found to be in position 3, the matching
+	// suffix "xxabc" is not found elsewhere in the pattern. However, its
+	// rightmost "abc" (at position 6) is a prefix of the whole pattern, so
+	// goodSuffixSkip[3] == shift+len(suffix) == 6+5 == 11.
+	goodSuffixSkip []int
+}
+
+func makeStringFinder(pattern string) *stringFinder {
+	f := &stringFinder{
+		pattern:        pattern,
+		goodSuffixSkip: make([]int, len(pattern)),
+	}
+	// last is the index of the last character in the pattern.
+	last := len(pattern) - 1
+
+	// Build bad character table.
+	// Bytes not in the pattern can skip one pattern's length.
+	for i := range f.badCharSkip {
+		f.badCharSkip[i] = len(pattern)
+	}
+	// The loop condition is < instead of <= so that the last byte does not
+	// have a zero distance to itself. Finding this byte out of place implies
+	// that it is not in the last position.
+	for i := 0; i < last; i++ {
+		f.badCharSkip[pattern[i]] = last - i
+	}
+
+	// Build good suffix table.
+	// First pass: set each value to the next index which starts a prefix of
+	// pattern.
+	lastPrefix := last
+	for i := last; i >= 0; i-- {
+		if HasPrefix(pattern, pattern[i+1:]) {
+			lastPrefix = i + 1
+		}
+		// lastPrefix is the shift, and (last-i) is len(suffix).
+		f.goodSuffixSkip[i] = lastPrefix + last - i
+	}
+	// Second pass: find repeats of pattern's suffix starting from the front.
+	for i := 0; i < last; i++ {
+		lenSuffix := longestCommonSuffix(pattern, pattern[1:i+1])
+		if pattern[i-lenSuffix] != pattern[last-lenSuffix] {
+			// (last-i) is the shift, and lenSuffix is len(suffix).
+			f.goodSuffixSkip[last-lenSuffix] = lenSuffix + last - i
+		}
+	}
+
+	return f
+}
+
+func longestCommonSuffix(a, b string) (i int) {
+	for ; i < len(a) && i < len(b); i++ {
+		if a[len(a)-1-i] != b[len(b)-1-i] {
+			break
+		}
+	}
+	return
+}
+
+// next returns the index in text of the first occurrence of the pattern. If
+// the pattern is not found, it returns -1.
+func (f *stringFinder) next(text string) int {
+	i := len(f.pattern) - 1
+	for i < len(text) {
+		// Compare backwards from the end until the first unmatching character.
+		j := len(f.pattern) - 1
+		for j >= 0 && text[i] == f.pattern[j] {
+			i--
+			j--
+		}
+		if j < 0 {
+			return i + 1 // match
+		}
+		i += max(f.badCharSkip[text[i]], f.goodSuffixSkip[j])
+	}
+	return -1
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
diff --git a/contrib/go/_std_1.18/src/strings/strings.go b/contrib/go/_std_1.18/src/strings/strings.go
new file mode 100644
index 0000000000..5793d9e26f
--- /dev/null
+++ b/contrib/go/_std_1.18/src/strings/strings.go
@@ -0,0 +1,1186 @@
+// 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 UTF-8 encoded strings.
+//
+// For information about UTF-8 strings in Go, see https://blog.golang.org/strings.
+package strings
+
+import (
+	"internal/bytealg"
+	"unicode"
+	"unicode/utf8"
+)
+
+// explode splits s into a slice of UTF-8 strings,
+// one string per Unicode character up to a maximum of n (n < 0 means no limit).
+// Invalid UTF-8 sequences become correct encodings of U+FFFD.
+func explode(s string, n int) []string {
+	l := utf8.RuneCountInString(s)
+	if n < 0 || n > l {
+		n = l
+	}
+	a := make([]string, n)
+	for i := 0; i < n-1; i++ {
+		ch, size := utf8.DecodeRuneInString(s)
+		a[i] = s[:size]
+		s = s[size:]
+		if ch == utf8.RuneError {
+			a[i] = string(utf8.RuneError)
+		}
+	}
+	if n > 0 {
+		a[n-1] = s
+	}
+	return a
+}
+
+// Count counts the number of non-overlapping instances of substr in s.
+// If substr is an empty string, Count returns 1 + the number of Unicode code points in s.
+func Count(s, substr string) int {
+	// special case
+	if len(substr) == 0 {
+		return utf8.RuneCountInString(s) + 1
+	}
+	if len(substr) == 1 {
+		return bytealg.CountString(s, substr[0])
+	}
+	n := 0
+	for {
+		i := Index(s, substr)
+		if i == -1 {
+			return n
+		}
+		n++
+		s = s[i+len(substr):]
+	}
+}
+
+// Contains reports whether substr is within s.
+func Contains(s, substr string) bool {
+	return Index(s, substr) >= 0
+}
+
+// ContainsAny reports whether any Unicode code points in chars are within s.
+func ContainsAny(s, chars string) bool {
+	return IndexAny(s, chars) >= 0
+}
+
+// ContainsRune reports whether the Unicode code point r is within s.
+func ContainsRune(s string, r rune) bool {
+	return IndexRune(s, r) >= 0
+}
+
+// LastIndex returns the index of the last instance of substr in s, or -1 if substr is not present in s.
+func LastIndex(s, substr string) int {
+	n := len(substr)
+	switch {
+	case n == 0:
+		return len(s)
+	case n == 1:
+		return LastIndexByte(s, substr[0])
+	case n == len(s):
+		if substr == s {
+			return 0
+		}
+		return -1
+	case n > len(s):
+		return -1
+	}
+	// Rabin-Karp search from the end of the string
+	hashss, pow := bytealg.HashStrRev(substr)
+	last := len(s) - n
+	var h uint32
+	for i := len(s) - 1; i >= last; i-- {
+		h = h*bytealg.PrimeRK + uint32(s[i])
+	}
+	if h == hashss && s[last:] == substr {
+		return last
+	}
+	for i := last - 1; i >= 0; i-- {
+		h *= bytealg.PrimeRK
+		h += uint32(s[i])
+		h -= pow * uint32(s[i+n])
+		if h == hashss && s[i:i+n] == substr {
+			return i
+		}
+	}
+	return -1
+}
+
+// IndexByte returns the index of the first instance of c in s, or -1 if c is not present in s.
+func IndexByte(s string, c byte) int {
+	return bytealg.IndexByteString(s, c)
+}
+
+// IndexRune returns the index of the first instance of the Unicode code point
+// r, or -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 string, r rune) int {
+	switch {
+	case 0 <= r && r < utf8.RuneSelf:
+		return IndexByte(s, byte(r))
+	case r == utf8.RuneError:
+		for i, r := range s {
+			if r == utf8.RuneError {
+				return i
+			}
+		}
+		return -1
+	case !utf8.ValidRune(r):
+		return -1
+	default:
+		return Index(s, string(r))
+	}
+}
+
+// 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 chars == "" {
+		// Avoid scanning all of s.
+		return -1
+	}
+	if len(chars) == 1 {
+		// Avoid scanning all of s.
+		r := rune(chars[0])
+		if r >= utf8.RuneSelf {
+			r = utf8.RuneError
+		}
+		return IndexRune(s, r)
+	}
+	if len(s) > 8 {
+		if as, isASCII := makeASCIISet(chars); isASCII {
+			for i := 0; i < len(s); i++ {
+				if as.contains(s[i]) {
+					return i
+				}
+			}
+			return -1
+		}
+	}
+	for i, c := range s {
+		if IndexRune(chars, c) >= 0 {
+			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 chars == "" {
+		// Avoid scanning all of s.
+		return -1
+	}
+	if len(s) == 1 {
+		rc := rune(s[0])
+		if rc >= utf8.RuneSelf {
+			rc = utf8.RuneError
+		}
+		if IndexRune(chars, rc) >= 0 {
+			return 0
+		}
+		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
+		}
+	}
+	if len(chars) == 1 {
+		rc := rune(chars[0])
+		if rc >= utf8.RuneSelf {
+			rc = utf8.RuneError
+		}
+		for i := len(s); i > 0; {
+			r, size := utf8.DecodeLastRuneInString(s[:i])
+			i -= size
+			if rc == r {
+				return i
+			}
+		}
+		return -1
+	}
+	for i := len(s); i > 0; {
+		r, size := utf8.DecodeLastRuneInString(s[:i])
+		i -= size
+		if IndexRune(chars, r) >= 0 {
+			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 string, c byte) int {
+	for i := len(s) - 1; i >= 0; i-- {
+		if s[i] == c {
+			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
+	}
+
+	a := make([]string, n)
+	n--
+	i := 0
+	for i < n {
+		m := Index(s, sep)
+		if m < 0 {
+			break
+		}
+		a[i] = s[:m+sepSave]
+		s = s[m+len(sep):]
+		i++
+	}
+	a[i] = s
+	return a[:i+1]
+}
+
+// SplitN slices s into substrings separated by sep and returns a slice of
+// the substrings between those separators.
+//
+// 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
+//
+// Edge cases for s and sep (for example, empty strings) are handled
+// as described in the documentation for Split.
+//
+// To split around the first instance of a separator, see Cut.
+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.
+//
+// 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
+//
+// Edge cases for s and sep (for example, empty strings) are handled
+// as described in the documentation for SplitAfter.
+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 s does not contain sep and sep is not empty, Split returns a
+// slice of length 1 whose only element is s.
+//
+// If sep is empty, Split splits after each UTF-8 sequence. If both s
+// and sep are empty, Split returns an empty slice.
+//
+// It is equivalent to SplitN with a count of -1.
+//
+// To split around the first instance of a separator, see Cut.
+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 s does not contain sep and sep is not empty, SplitAfter returns
+// a slice of length 1 whose only element is s.
+//
+// If sep is empty, SplitAfter splits after each UTF-8 sequence. If
+// both s and sep are empty, SplitAfter returns an empty slice.
+//
+// It is equivalent to SplitAfterN with a count of -1.
+func SplitAfter(s, sep string) []string {
+	return genSplit(s, sep, len(sep), -1)
+}
+
+var asciiSpace = [256]uint8{'\t': 1, '\n': 1, '\v': 1, '\f': 1, '\r': 1, ' ': 1}
+
+// Fields splits the string s around each instance of one or more consecutive white space
+// characters, as defined by unicode.IsSpace, returning a slice of substrings of s or an
+// empty slice if s contains only white space.
+func Fields(s string) []string {
+	// 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 string are not ASCII.
+		return FieldsFunc(s, unicode.IsSpace)
+	}
+	// ASCII fast path
+	a := make([]string, 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]
+		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:]
+	}
+	return a
+}
+
+// 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)
+// and assumes that f always returns the same value for a given c.
+func FieldsFunc(s string, f func(rune) bool) []string {
+	// 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.
+	// Doing this in a separate pass (rather than slicing the string s
+	// and collecting the result substrings right away) is significantly
+	// more efficient, possibly due to cache effects.
+	start := -1 // valid span start if >= 0
+	for end, rune := range s {
+		if f(rune) {
+			if start >= 0 {
+				spans = append(spans, span{start, end})
+				// Set start to a negative value.
+				// Note: using -1 here consistently and reproducibly
+				// slows down this code by a several percent on amd64.
+				start = ^start
+			}
+		} else {
+			if start < 0 {
+				start = end
+			}
+		}
+	}
+
+	// Last field might end at EOF.
+	if start >= 0 {
+		spans = append(spans, span{start, len(s)})
+	}
+
+	// Create strings from recorded field indices.
+	a := make([]string, len(spans))
+	for i, span := range spans {
+		a[i] = s[span.start:span.end]
+	}
+
+	return a
+}
+
+// Join concatenates the elements of its first argument to create a single string. The separator
+// string sep is placed between elements in the resulting string.
+func Join(elems []string, sep string) string {
+	switch len(elems) {
+	case 0:
+		return ""
+	case 1:
+		return elems[0]
+	}
+	n := len(sep) * (len(elems) - 1)
+	for i := 0; i < len(elems); i++ {
+		n += len(elems[i])
+	}
+
+	var b Builder
+	b.Grow(n)
+	b.WriteString(elems[0])
+	for _, s := range elems[1:] {
+		b.WriteString(sep)
+		b.WriteString(s)
+	}
+	return b.String()
+}
+
+// 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.
+
+	// The output buffer b is initialized on demand, the first
+	// time a character differs.
+	var b Builder
+
+	for i, c := range s {
+		r := mapping(c)
+		if r == c && c != utf8.RuneError {
+			continue
+		}
+
+		var width int
+		if c == utf8.RuneError {
+			c, width = utf8.DecodeRuneInString(s[i:])
+			if width != 1 && r == c {
+				continue
+			}
+		} else {
+			width = utf8.RuneLen(c)
+		}
+
+		b.Grow(len(s) + utf8.UTFMax)
+		b.WriteString(s[:i])
+		if r >= 0 {
+			b.WriteRune(r)
+		}
+
+		s = s[i+width:]
+		break
+	}
+
+	// Fast path for unchanged input
+	if b.Cap() == 0 { // didn't call b.Grow above
+		return s
+	}
+
+	for _, c := range s {
+		r := mapping(c)
+
+		if r >= 0 {
+			// common case
+			// Due to inlining, it is more performant to determine if WriteByte should be
+			// invoked rather than always call WriteRune
+			if r < utf8.RuneSelf {
+				b.WriteByte(byte(r))
+			} else {
+				// r is not a ASCII rune.
+				b.WriteRune(r)
+			}
+		}
+	}
+
+	return b.String()
+}
+
+// Repeat returns a new string consisting of count copies of the string s.
+//
+// It panics if count is negative or if
+// the result of (len(s) * count) overflows.
+func Repeat(s string, count int) string {
+	if count == 0 {
+		return ""
+	}
+
+	// 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("strings: negative Repeat count")
+	} else if len(s)*count/count != len(s) {
+		panic("strings: Repeat count causes overflow")
+	}
+
+	n := len(s) * count
+	var b Builder
+	b.Grow(n)
+	b.WriteString(s)
+	for b.Len() < n {
+		if b.Len() <= n/2 {
+			b.WriteString(b.String())
+		} else {
+			b.WriteString(b.String()[:n-b.Len()])
+			break
+		}
+	}
+	return b.String()
+}
+
+// ToUpper returns s with all Unicode letters mapped to their upper case.
+func ToUpper(s string) string {
+	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 strings.
+		if !hasLower {
+			return s
+		}
+		var b Builder
+		b.Grow(len(s))
+		for i := 0; i < len(s); i++ {
+			c := s[i]
+			if 'a' <= c && c <= 'z' {
+				c -= 'a' - 'A'
+			}
+			b.WriteByte(c)
+		}
+		return b.String()
+	}
+	return Map(unicode.ToUpper, s)
+}
+
+// ToLower returns s with all Unicode letters mapped to their lower case.
+func ToLower(s string) string {
+	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 strings.
+		if !hasUpper {
+			return s
+		}
+		var b Builder
+		b.Grow(len(s))
+		for i := 0; i < len(s); i++ {
+			c := s[i]
+			if 'A' <= c && c <= 'Z' {
+				c += 'a' - 'A'
+			}
+			b.WriteByte(c)
+		}
+		return b.String()
+	}
+	return Map(unicode.ToLower, s)
+}
+
+// ToTitle returns a copy of the string s with all Unicode letters mapped to
+// their Unicode 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 using the case mapping specified by c.
+func ToUpperSpecial(c unicode.SpecialCase, s string) string {
+	return Map(c.ToUpper, s)
+}
+
+// ToLowerSpecial returns a copy of the string s with all Unicode letters mapped to their
+// lower case using the case mapping specified by c.
+func ToLowerSpecial(c unicode.SpecialCase, s string) string {
+	return Map(c.ToLower, s)
+}
+
+// ToTitleSpecial returns a copy of the string s with all Unicode letters mapped to their
+// Unicode title case, giving priority to the special casing rules.
+func ToTitleSpecial(c unicode.SpecialCase, s string) string {
+	return Map(c.ToTitle, s)
+}
+
+// ToValidUTF8 returns a copy of the string s with each run of invalid UTF-8 byte sequences
+// replaced by the replacement string, which may be empty.
+func ToValidUTF8(s, replacement string) string {
+	var b Builder
+
+	for i, c := range s {
+		if c != utf8.RuneError {
+			continue
+		}
+
+		_, wid := utf8.DecodeRuneInString(s[i:])
+		if wid == 1 {
+			b.Grow(len(s) + len(replacement))
+			b.WriteString(s[:i])
+			s = s[i:]
+			break
+		}
+	}
+
+	// Fast path for unchanged input
+	if b.Cap() == 0 { // didn't call b.Grow above
+		return s
+	}
+
+	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.WriteByte(c)
+			continue
+		}
+		_, wid := utf8.DecodeRuneInString(s[i:])
+		if wid == 1 {
+			i++
+			if !invalid {
+				invalid = true
+				b.WriteString(replacement)
+			}
+			continue
+		}
+		invalid = false
+		b.WriteString(s[i : i+wid])
+		i += wid
+	}
+
+	return b.String()
+}
+
+// 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 Unicode title case.
+//
+// Deprecated: The rule Title uses for word boundaries does not handle Unicode
+// punctuation properly. Use golang.org/x/text/cases instead.
+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 {
+	for i, r := range s {
+		if f(r) == truth {
+			return i
+		}
+	}
+	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
+}
+
+// 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.
+// This allocates a total of 32 bytes even though the upper half
+// is unused to avoid bounds checks in asciiSet.contains.
+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/32] |= 1 << (c % 32)
+	}
+	return as, true
+}
+
+// contains reports whether c is inside the set.
+func (as *asciiSet) contains(c byte) bool {
+	return (as[c/32] & (1 << (c % 32))) != 0
+}
+
+// Trim returns a slice of the string s with all leading and
+// trailing Unicode code points contained in cutset removed.
+func Trim(s, cutset string) string {
+	if s == "" || cutset == "" {
+		return s
+	}
+	if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
+		return trimLeftByte(trimRightByte(s, cutset[0]), cutset[0])
+	}
+	if as, ok := makeASCIISet(cutset); ok {
+		return trimLeftASCII(trimRightASCII(s, &as), &as)
+	}
+	return trimLeftUnicode(trimRightUnicode(s, cutset), cutset)
+}
+
+// TrimLeft returns a slice of the string s with all leading
+// Unicode code points contained in cutset removed.
+//
+// To remove a prefix, use TrimPrefix instead.
+func TrimLeft(s, cutset string) string {
+	if s == "" || cutset == "" {
+		return s
+	}
+	if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
+		return trimLeftByte(s, cutset[0])
+	}
+	if as, ok := makeASCIISet(cutset); ok {
+		return trimLeftASCII(s, &as)
+	}
+	return trimLeftUnicode(s, cutset)
+}
+
+func trimLeftByte(s string, c byte) string {
+	for len(s) > 0 && s[0] == c {
+		s = s[1:]
+	}
+	return s
+}
+
+func trimLeftASCII(s string, as *asciiSet) string {
+	for len(s) > 0 {
+		if !as.contains(s[0]) {
+			break
+		}
+		s = s[1:]
+	}
+	return s
+}
+
+func trimLeftUnicode(s, cutset string) string {
+	for len(s) > 0 {
+		r, n := rune(s[0]), 1
+		if r >= utf8.RuneSelf {
+			r, n = utf8.DecodeRuneInString(s)
+		}
+		if !ContainsRune(cutset, r) {
+			break
+		}
+		s = s[n:]
+	}
+	return s
+}
+
+// TrimRight returns a slice of the string s, with all trailing
+// Unicode code points contained in cutset removed.
+//
+// To remove a suffix, use TrimSuffix instead.
+func TrimRight(s, cutset string) string {
+	if s == "" || cutset == "" {
+		return s
+	}
+	if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
+		return trimRightByte(s, cutset[0])
+	}
+	if as, ok := makeASCIISet(cutset); ok {
+		return trimRightASCII(s, &as)
+	}
+	return trimRightUnicode(s, cutset)
+}
+
+func trimRightByte(s string, c byte) string {
+	for len(s) > 0 && s[len(s)-1] == c {
+		s = s[:len(s)-1]
+	}
+	return s
+}
+
+func trimRightASCII(s string, as *asciiSet) string {
+	for len(s) > 0 {
+		if !as.contains(s[len(s)-1]) {
+			break
+		}
+		s = s[:len(s)-1]
+	}
+	return s
+}
+
+func trimRightUnicode(s, cutset string) string {
+	for len(s) > 0 {
+		r, n := rune(s[len(s)-1]), 1
+		if r >= utf8.RuneSelf {
+			r, n = utf8.DecodeLastRuneInString(s)
+		}
+		if !ContainsRune(cutset, r) {
+			break
+		}
+		s = s[:len(s)-n]
+	}
+	return s
+}
+
+// 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 {
+	// 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.
+	return s[start:stop]
+}
+
+// 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.
+	var b Builder
+	b.Grow(len(s) + n*(len(new)-len(old)))
+	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)
+		}
+		b.WriteString(s[start:j])
+		b.WriteString(new)
+		start = j + len(old)
+	}
+	b.WriteString(s[start:])
+	return b.String()
+}
+
+// ReplaceAll returns a copy of the string s with all
+// 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.
+func ReplaceAll(s, old, new string) string {
+	return Replace(s, old, new, -1)
+}
+
+// EqualFold reports whether s and t, interpreted as UTF-8 strings,
+// are equal under Unicode case-folding, which is a more general
+// form of case-insensitivity.
+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 {
+			// 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 s == t
+}
+
+// Index returns the index of the first instance of substr in s, or -1 if substr is not present in s.
+func Index(s, substr string) int {
+	n := len(substr)
+	switch {
+	case n == 0:
+		return 0
+	case n == 1:
+		return IndexByte(s, substr[0])
+	case n == len(s):
+		if substr == s {
+			return 0
+		}
+		return -1
+	case n > len(s):
+		return -1
+	case n <= bytealg.MaxLen:
+		// Use brute force when s and substr both are small
+		if len(s) <= bytealg.MaxBruteForce {
+			return bytealg.IndexString(s, substr)
+		}
+		c0 := substr[0]
+		c1 := substr[1]
+		i := 0
+		t := len(s) - n + 1
+		fails := 0
+		for i < t {
+			if s[i] != c0 {
+				// IndexByte is faster than bytealg.IndexString, so use it as long as
+				// we're not getting lots of false positives.
+				o := IndexByte(s[i+1:t], c0)
+				if o < 0 {
+					return -1
+				}
+				i += o + 1
+			}
+			if s[i+1] == c1 && s[i:i+n] == substr {
+				return i
+			}
+			fails++
+			i++
+			// Switch to bytealg.IndexString when IndexByte produces too many false positives.
+			if fails > bytealg.Cutover(i) {
+				r := bytealg.IndexString(s[i:], substr)
+				if r >= 0 {
+					return r + i
+				}
+				return -1
+			}
+		}
+		return -1
+	}
+	c0 := substr[0]
+	c1 := substr[1]
+	i := 0
+	t := len(s) - n + 1
+	fails := 0
+	for i < t {
+		if s[i] != c0 {
+			o := IndexByte(s[i+1:t], c0)
+			if o < 0 {
+				return -1
+			}
+			i += o + 1
+		}
+		if s[i+1] == c1 && s[i:i+n] == substr {
+			return i
+		}
+		i++
+		fails++
+		if fails >= 4+i>>4 && i < t {
+			// See comment in ../bytes/bytes.go.
+			j := bytealg.IndexRabinKarp(s[i:], substr)
+			if j < 0 {
+				return -1
+			}
+			return i + j
+		}
+	}
+	return -1
+}
+
+// Cut slices s around the first instance of sep,
+// returning the text before and after sep.
+// The found result reports whether sep appears in s.
+// If sep does not appear in s, cut returns s, "", false.
+func Cut(s, sep string) (before, after string, found bool) {
+	if i := Index(s, sep); i >= 0 {
+		return s[:i], s[i+len(sep):], true
+	}
+	return s, "", false
+}