libgo/go/runtime/string.go - gofrontend - Git at Google

 // Copyright 2014 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 runtime

 import (
 	"internal/bytealg"
 	"unsafe"
 )

 // For gccgo, use go:linkname to export compiler-called functions.
 //
 //go:linkname concatstrings
 //go:linkname slicebytetostring
 //go:linkname slicebytetostringtmp
 //go:linkname stringtoslicebyte
 //go:linkname stringtoslicerune
 //go:linkname slicerunetostring
 //go:linkname intstring
 // Temporary for C code to call:
 //go:linkname gostringnocopy
 //go:linkname findnull

 // The constant is known to the compiler.
 // There is no fundamental theory behind this number.
 const tmpStringBufSize = 32

 type tmpBuf [tmpStringBufSize]byte

 // concatstrings implements a Go string concatenation x+y+z+...
 // The operands are passed in the slice a.
 // If buf != nil, the compiler has determined that the result does not
 // escape the calling function, so the string data can be stored in buf
 // if small enough.
 func concatstrings(buf *tmpBuf, p *string, n int) string {
 	var a []string
 	*(*slice)(unsafe.Pointer(&a)) = slice{unsafe.Pointer(p), n, n}
 	// idx := 0
 	l := 0
 	count := 0
 	for _, x := range a {
 		n := len(x)
 		if n == 0 {
 			continue
 		}
 		if l+n < l {
 			throw("string concatenation too long")
 		}
 		l += n
 		count++
 		// idx = i
 	}
 	if count == 0 {
 		return ""
 	}

 	// If there is just one string and either it is not on the stack
 	// or our result does not escape the calling frame (buf != nil),
 	// then we can return that string directly.
 	// Commented out for gccgo--no implementation of stringDataOnStack.
 	// if count == 1 && (buf != nil || !stringDataOnStack(a[idx])) {
 	// 	return a[idx]
 	// }
 	s, b := rawstringtmp(buf, l)
 	for _, x := range a {
 		copy(b, x)
 		b = b[len(x):]
 	}
 	return s
 }

 // slicebytetostring converts a byte slice to a string.
 // It is inserted by the compiler into generated code.
 // ptr is a pointer to the first element of the slice;
 // n is the length of the slice.
 // Buf is a fixed-size buffer for the result,
 // it is not nil if the result does not escape.
 func slicebytetostring(buf *tmpBuf, ptr *byte, n int) (str string) {
 	if n == 0 {
 		// Turns out to be a relatively common case.
 		// Consider that you want to parse out data between parens in "foo()bar",
 		// you find the indices and convert the subslice to string.
 		return ""
 	}
 	if raceenabled {
 		racereadrangepc(unsafe.Pointer(ptr),
 			uintptr(n),
 			getcallerpc(),
 			funcPC(slicebytetostring))
 	}
 	if msanenabled {
 		msanread(unsafe.Pointer(ptr), uintptr(n))
 	}
 	if n == 1 {
 		stringStructOf(&str).str = unsafe.Pointer(&staticbytes[*ptr])
 		stringStructOf(&str).len = 1
 		return
 	}

 	var p unsafe.Pointer
 	if buf != nil && n <= len(buf) {
 		p = unsafe.Pointer(buf)
 	} else {
 		p = mallocgc(uintptr(n), nil, false)
 	}
 	stringStructOf(&str).str = p
 	stringStructOf(&str).len = n
 	memmove(p, unsafe.Pointer(ptr), uintptr(n))
 	return
 }

 func rawstringtmp(buf *tmpBuf, l int) (s string, b []byte) {
 	if buf != nil && l <= len(buf) {
 		b = buf[:l]
 		s = slicebytetostringtmp(&b[0], len(b))
 	} else {
 		s, b = rawstring(l)
 	}
 	return
 }

 // slicebytetostringtmp returns a "string" referring to the actual []byte bytes.
 //
 // Callers need to ensure that the returned string will not be used after
 // the calling goroutine modifies the original slice or synchronizes with
 // another goroutine.
 //
 // The function is only called when instrumenting
 // and otherwise intrinsified by the compiler.
 //
 // Some internal compiler optimizations use this function.
 // - Used for m[T1{... Tn{..., string(k), ...} ...}] and m[string(k)]
 //   where k is []byte, T1 to Tn is a nesting of struct and array literals.
 // - Used for "<"+string(b)+">" concatenation where b is []byte.
 // - Used for string(b)=="foo" comparison where b is []byte.
 func slicebytetostringtmp(ptr *byte, n int) (str string) {
 	if raceenabled && n > 0 {
 		racereadrangepc(unsafe.Pointer(ptr),
 			uintptr(n),
 			getcallerpc(),
 			funcPC(slicebytetostringtmp))
 	}
 	if msanenabled && n > 0 {
 		msanread(unsafe.Pointer(ptr), uintptr(n))
 	}
 	stringStructOf(&str).str = unsafe.Pointer(ptr)
 	stringStructOf(&str).len = n
 	return
 }

 func stringtoslicebyte(buf *tmpBuf, s string) []byte {
 	var b []byte
 	if buf != nil && len(s) <= len(buf) {
 		*buf = tmpBuf{}
 		b = buf[:len(s)]
 	} else {
 		b = rawbyteslice(len(s))
 	}
 	copy(b, s)
 	return b
 }

 func stringtoslicerune(buf *[tmpStringBufSize]rune, s string) []rune {
 	// two passes.
 	// unlike slicerunetostring, no race because strings are immutable.
 	n := 0
 	for range s {
 		n++
 	}

 	var a []rune
 	if buf != nil && n <= len(buf) {
 		*buf = [tmpStringBufSize]rune{}
 		a = buf[:n]
 	} else {
 		a = rawruneslice(n)
 	}

 	n = 0
 	for _, r := range s {
 		a[n] = r
 		n++
 	}
 	return a
 }

 func slicerunetostring(buf *tmpBuf, a []rune) string {
 	if raceenabled && len(a) > 0 {
 		racereadrangepc(unsafe.Pointer(&a[0]),
 			uintptr(len(a))*unsafe.Sizeof(a[0]),
 			getcallerpc(),
 			funcPC(slicerunetostring))
 	}
 	if msanenabled && len(a) > 0 {
 		msanread(unsafe.Pointer(&a[0]), uintptr(len(a))*unsafe.Sizeof(a[0]))
 	}
 	var dum [4]byte
 	size1 := 0
 	for _, r := range a {
 		size1 += encoderune(dum[:], r)
 	}
 	s, b := rawstringtmp(buf, size1+3)
 	size2 := 0
 	for _, r := range a {
 		// check for race
 		if size2 >= size1 {
 			break
 		}
 		size2 += encoderune(b[size2:], r)
 	}
 	return s[:size2]
 }

 type stringStruct struct {
 	str unsafe.Pointer
 	len int
 }

 // Variant with *byte pointer type for DWARF debugging.
 type stringStructDWARF struct {
 	str *byte
 	len int
 }

 func stringStructOf(sp *string) *stringStruct {
 	return (*stringStruct)(unsafe.Pointer(sp))
 }

 func intstring(buf *[4]byte, v int64) (s string) {
 	if v >= 0 && v < runeSelf {
 		stringStructOf(&s).str = unsafe.Pointer(&staticbytes[v])
 		stringStructOf(&s).len = 1
 		return
 	}

 	var b []byte
 	if buf != nil {
 		b = buf[:]
 		s = slicebytetostringtmp(&b[0], len(b))
 	} else {
 		s, b = rawstring(4)
 	}
 	if int64(rune(v)) != v {
 		v = runeError
 	}
 	n := encoderune(b, rune(v))
 	return s[:n]
 }

 // rawstring allocates storage for a new string. The returned
 // string and byte slice both refer to the same storage.
 // The storage is not zeroed. Callers should use
 // b to set the string contents and then drop b.
 func rawstring(size int) (s string, b []byte) {
 	p := mallocgc(uintptr(size), nil, false)

 	stringStructOf(&s).str = p
 	stringStructOf(&s).len = size

 	*(*slice)(unsafe.Pointer(&b)) = slice{p, size, size}

 	return
 }

 // rawbyteslice allocates a new byte slice. The byte slice is not zeroed.
 func rawbyteslice(size int) (b []byte) {
 	cap := roundupsize(uintptr(size))
 	p := mallocgc(cap, nil, false)
 	if cap != uintptr(size) {
 		memclrNoHeapPointers(add(p, uintptr(size)), cap-uintptr(size))
 	}

 	*(*slice)(unsafe.Pointer(&b)) = slice{p, size, int(cap)}
 	return
 }

 // rawruneslice allocates a new rune slice. The rune slice is not zeroed.
 func rawruneslice(size int) (b []rune) {
 	if uintptr(size) > maxAlloc/4 {
 		throw("out of memory")
 	}
 	mem := roundupsize(uintptr(size) * 4)
 	p := mallocgc(mem, nil, false)
 	if mem != uintptr(size)*4 {
 		memclrNoHeapPointers(add(p, uintptr(size)*4), mem-uintptr(size)*4)
 	}

 	*(*slice)(unsafe.Pointer(&b)) = slice{p, size, int(mem / 4)}
 	return
 }

 // used by cmd/cgo
 func gobytes(p *byte, n int) (b []byte) {
 	if n == 0 {
 		return make([]byte, 0)
 	}

 	if n < 0 || uintptr(n) > maxAlloc {
 		panic(errorString("gobytes: length out of range"))
 	}

 	bp := mallocgc(uintptr(n), nil, false)
 	memmove(bp, unsafe.Pointer(p), uintptr(n))

 	*(*slice)(unsafe.Pointer(&b)) = slice{bp, n, n}
 	return
 }

 // This is exported via linkname to assembly in syscall (for Plan9).
 //go:linkname gostring
 func gostring(p *byte) string {
 	l := findnull(p)
 	if l == 0 {
 		return ""
 	}
 	s, b := rawstring(l)
 	memmove(unsafe.Pointer(&b[0]), unsafe.Pointer(p), uintptr(l))
 	return s
 }

 func gostringn(p *byte, l int) string {
 	if l == 0 {
 		return ""
 	}
 	s, b := rawstring(l)
 	memmove(unsafe.Pointer(&b[0]), unsafe.Pointer(p), uintptr(l))
 	return s
 }

 func index(s, t string) int {
 	if len(t) == 0 {
 		return 0
 	}
 	for i := 0; i < len(s); i++ {
 		if s[i] == t[0] && hasPrefix(s[i:], t) {
 			return i
 		}
 	}
 	return -1
 }

 func contains(s, t string) bool {
 	return index(s, t) >= 0
 }

 func hasPrefix(s, prefix string) bool {
 	return len(s) >= len(prefix) && s[:len(prefix)] == prefix
 }

 func hasSuffix(s, suffix string) bool {
 	return len(s) >= len(suffix) && s[len(s)-len(suffix):] == suffix
 }

 const (
 	maxUint = ^uint(0)
 	maxInt  = int(maxUint >> 1)
 )

 // atoi parses an int from a string s.
 // The bool result reports whether s is a number
 // representable by a value of type int.
 func atoi(s string) (int, bool) {
 	if s == "" {
 		return 0, false
 	}

 	neg := false
 	if s[0] == '-' {
 		neg = true
 		s = s[1:]
 	}

 	un := uint(0)
 	for i := 0; i < len(s); i++ {
 		c := s[i]
 		if c < '0' || c > '9' {
 			return 0, false
 		}
 		if un > maxUint/10 {
 			// overflow
 			return 0, false
 		}
 		un *= 10
 		un1 := un + uint(c) - '0'
 		if un1 < un {
 			// overflow
 			return 0, false
 		}
 		un = un1
 	}

 	if !neg && un > uint(maxInt) {
 		return 0, false
 	}
 	if neg && un > uint(maxInt)+1 {
 		return 0, false
 	}

 	n := int(un)
 	if neg {
 		n = -n
 	}

 	return n, true
 }

 // atoi32 is like atoi but for integers
 // that fit into an int32.
 func atoi32(s string) (int32, bool) {
 	if n, ok := atoi(s); n == int(int32(n)) {
 		return int32(n), ok
 	}
 	return 0, false
 }

 //go:nosplit
 func findnull(s *byte) int {
 	if s == nil {
 		return 0
 	}

 	// Avoid IndexByteString on Plan 9 because it uses SSE instructions
 	// on x86 machines, and those are classified as floating point instructions,
 	// which are illegal in a note handler.
 	if GOOS == "plan9" {
 		p := (*[maxAlloc/2 - 1]byte)(unsafe.Pointer(s))
 		l := 0
 		for p[l] != 0 {
 			l++
 		}
 		return l
 	}

 	// pageSize is the unit we scan at a time looking for NULL.
 	// It must be the minimum page size for any architecture Go
 	// runs on. It's okay (just a minor performance loss) if the
 	// actual system page size is larger than this value.
 	const pageSize = 4096

 	offset := 0
 	ptr := unsafe.Pointer(s)
 	// IndexByteString uses wide reads, so we need to be careful
 	// with page boundaries. Call IndexByteString on
 	// [ptr, endOfPage) interval.
 	safeLen := int(pageSize - uintptr(ptr)%pageSize)

 	for {
 		t := *(*string)(unsafe.Pointer(&stringStruct{ptr, safeLen}))
 		// Check one page at a time.
 		if i := bytealg.IndexByteString(t, 0); i != -1 {
 			return offset + i
 		}
 		// Move to next page
 		ptr = unsafe.Pointer(uintptr(ptr) + uintptr(safeLen))
 		offset += safeLen
 		safeLen = pageSize
 	}
 }

 func findnullw(s *uint16) int {
 	if s == nil {
 		return 0
 	}
 	p := (*[maxAlloc/2/2 - 1]uint16)(unsafe.Pointer(s))
 	l := 0
 	for p[l] != 0 {
 		l++
 	}
 	return l
 }

 //go:nosplit
 func gostringnocopy(str *byte) string {
 	ss := stringStruct{str: unsafe.Pointer(str), len: findnull(str)}
 	s := *(*string)(unsafe.Pointer(&ss))
 	return s
 }

 func gostringw(strw *uint16) string {
 	var buf [8]byte
 	str := (*[maxAlloc/2/2 - 1]uint16)(unsafe.Pointer(strw))
 	n1 := 0
 	for i := 0; str[i] != 0; i++ {
 		n1 += encoderune(buf[:], rune(str[i]))
 	}
 	s, b := rawstring(n1 + 4)
 	n2 := 0
 	for i := 0; str[i] != 0; i++ {
 		// check for race
 		if n2 >= n1 {
 			break
 		}
 		n2 += encoderune(b[n2:], rune(str[i]))
 	}
 	b[n2] = 0 // for luck
 	return s[:n2]
 }

 // These two functions are called by code generated by cgo -gccgo.

 //go:linkname __go_byte_array_to_string __go_byte_array_to_string
 func __go_byte_array_to_string(p unsafe.Pointer, l int) string {
 	if l == 0 {
 		return ""
 	}
 	s, c := rawstringtmp(nil, l)
 	memmove(unsafe.Pointer(&c[0]), p, uintptr(l))
 	return s
 }

 //go:linkname __go_string_to_byte_array __go_string_to_byte_array
 func __go_string_to_byte_array(s string) []byte {
 	return stringtoslicebyte(nil, s)
 }

 // parseRelease parses a dot-separated version number. It follows the
 // semver syntax, but allows the minor and patch versions to be
 // elided.
 func parseRelease(rel string) (major, minor, patch int, ok bool) {
 	// Strip anything after a dash or plus.
 	for i := 0; i < len(rel); i++ {
 		if rel[i] == '-' || rel[i] == '+' {
 			rel = rel[:i]
 			break
 		}
 	}

 	next := func() (int, bool) {
 		for i := 0; i < len(rel); i++ {
 			if rel[i] == '.' {
 				ver, ok := atoi(rel[:i])
 				rel = rel[i+1:]
 				return ver, ok
 			}
 		}
 		ver, ok := atoi(rel)
 		rel = ""
 		return ver, ok
 	}
 	if major, ok = next(); !ok || rel == "" {
 		return
 	}
 	if minor, ok = next(); !ok || rel == "" {
 		return
 	}
 	patch, ok = next()
 	return
 }
	// Copyright 2014 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 runtime

	import (
	"internal/bytealg"
	"unsafe"
	)

	// For gccgo, use go:linkname to export compiler-called functions.
	//
	//go:linkname concatstrings
	//go:linkname slicebytetostring
	//go:linkname slicebytetostringtmp
	//go:linkname stringtoslicebyte
	//go:linkname stringtoslicerune
	//go:linkname slicerunetostring
	//go:linkname intstring
	// Temporary for C code to call:
	//go:linkname gostringnocopy
	//go:linkname findnull

	// The constant is known to the compiler.
	// There is no fundamental theory behind this number.
	const tmpStringBufSize = 32

	type tmpBuf [tmpStringBufSize]byte

	// concatstrings implements a Go string concatenation x+y+z+...
	// The operands are passed in the slice a.
	// If buf != nil, the compiler has determined that the result does not
	// escape the calling function, so the string data can be stored in buf
	// if small enough.
	func concatstrings(buf tmpBuf, p string, n int) string {
	var a []string
	(slice)(unsafe.Pointer(&a)) = slice{unsafe.Pointer(p), n, n}
	// idx := 0
	l := 0
	count := 0
	for _, x := range a {
	n := len(x)
	if n == 0 {
	continue
	}
	if l+n < l {
	throw("string concatenation too long")
	}
	l += n
	count++
	// idx = i
	}
	if count == 0 {
	return ""
	}

	// If there is just one string and either it is not on the stack
	// or our result does not escape the calling frame (buf != nil),
	// then we can return that string directly.
	// Commented out for gccgo--no implementation of stringDataOnStack.
	// if count == 1 && (buf != nil \|\| !stringDataOnStack(a[idx])) {
	// return a[idx]
	// }
	s, b := rawstringtmp(buf, l)
	for _, x := range a {
	copy(b, x)
	b = b[len(x):]
	}
	return s
	}

	// slicebytetostring converts a byte slice to a string.
	// It is inserted by the compiler into generated code.
	// ptr is a pointer to the first element of the slice;
	// n is the length of the slice.
	// Buf is a fixed-size buffer for the result,
	// it is not nil if the result does not escape.
	func slicebytetostring(buf tmpBuf, ptr byte, n int) (str string) {
	if n == 0 {
	// Turns out to be a relatively common case.
	// Consider that you want to parse out data between parens in "foo()bar",
	// you find the indices and convert the subslice to string.
	return ""
	}
	if raceenabled {
	racereadrangepc(unsafe.Pointer(ptr),
	uintptr(n),
	getcallerpc(),
	funcPC(slicebytetostring))
	}
	if msanenabled {
	msanread(unsafe.Pointer(ptr), uintptr(n))
	}
	if n == 1 {
	stringStructOf(&str).str = unsafe.Pointer(&staticbytes[*ptr])
	stringStructOf(&str).len = 1
	return
	}

	var p unsafe.Pointer
	if buf != nil && n <= len(buf) {
	p = unsafe.Pointer(buf)
	} else {
	p = mallocgc(uintptr(n), nil, false)
	}
	stringStructOf(&str).str = p
	stringStructOf(&str).len = n
	memmove(p, unsafe.Pointer(ptr), uintptr(n))
	return
	}

	func rawstringtmp(buf *tmpBuf, l int) (s string, b []byte) {
	if buf != nil && l <= len(buf) {
	b = buf[:l]
	s = slicebytetostringtmp(&b[0], len(b))
	} else {
	s, b = rawstring(l)
	}
	return
	}

	// slicebytetostringtmp returns a "string" referring to the actual []byte bytes.
	//
	// Callers need to ensure that the returned string will not be used after
	// the calling goroutine modifies the original slice or synchronizes with
	// another goroutine.
	//
	// The function is only called when instrumenting
	// and otherwise intrinsified by the compiler.
	//
	// Some internal compiler optimizations use this function.
	// - Used for m[T1{... Tn{..., string(k), ...} ...}] and m[string(k)]
	// where k is []byte, T1 to Tn is a nesting of struct and array literals.
	// - Used for "<"+string(b)+">" concatenation where b is []byte.
	// - Used for string(b)=="foo" comparison where b is []byte.
	func slicebytetostringtmp(ptr *byte, n int) (str string) {
	if raceenabled && n > 0 {
	racereadrangepc(unsafe.Pointer(ptr),
	uintptr(n),
	getcallerpc(),
	funcPC(slicebytetostringtmp))
	}
	if msanenabled && n > 0 {
	msanread(unsafe.Pointer(ptr), uintptr(n))
	}
	stringStructOf(&str).str = unsafe.Pointer(ptr)
	stringStructOf(&str).len = n
	return
	}

	func stringtoslicebyte(buf *tmpBuf, s string) []byte {
	var b []byte
	if buf != nil && len(s) <= len(buf) {
	*buf = tmpBuf{}
	b = buf[:len(s)]
	} else {
	b = rawbyteslice(len(s))
	}
	copy(b, s)
	return b
	}

	func stringtoslicerune(buf *[tmpStringBufSize]rune, s string) []rune {
	// two passes.
	// unlike slicerunetostring, no race because strings are immutable.
	n := 0
	for range s {
	n++
	}

	var a []rune
	if buf != nil && n <= len(buf) {
	*buf = [tmpStringBufSize]rune{}
	a = buf[:n]
	} else {
	a = rawruneslice(n)
	}

	n = 0
	for _, r := range s {
	a[n] = r
	n++
	}
	return a
	}

	func slicerunetostring(buf *tmpBuf, a []rune) string {
	if raceenabled && len(a) > 0 {
	racereadrangepc(unsafe.Pointer(&a[0]),
	uintptr(len(a))*unsafe.Sizeof(a[0]),
	getcallerpc(),
	funcPC(slicerunetostring))
	}
	if msanenabled && len(a) > 0 {
	msanread(unsafe.Pointer(&a[0]), uintptr(len(a))*unsafe.Sizeof(a[0]))
	}
	var dum [4]byte
	size1 := 0
	for _, r := range a {
	size1 += encoderune(dum[:], r)
	}
	s, b := rawstringtmp(buf, size1+3)
	size2 := 0
	for _, r := range a {
	// check for race
	if size2 >= size1 {
	break
	}
	size2 += encoderune(b[size2:], r)
	}
	return s[:size2]
	}

	type stringStruct struct {
	str unsafe.Pointer
	len int
	}

	// Variant with *byte pointer type for DWARF debugging.
	type stringStructDWARF struct {
	str *byte
	len int
	}

	func stringStructOf(sp string) stringStruct {
	return (*stringStruct)(unsafe.Pointer(sp))
	}

	func intstring(buf *[4]byte, v int64) (s string) {
	if v >= 0 && v < runeSelf {
	stringStructOf(&s).str = unsafe.Pointer(&staticbytes[v])
	stringStructOf(&s).len = 1
	return
	}

	var b []byte
	if buf != nil {
	b = buf[:]
	s = slicebytetostringtmp(&b[0], len(b))
	} else {
	s, b = rawstring(4)
	}
	if int64(rune(v)) != v {
	v = runeError
	}
	n := encoderune(b, rune(v))
	return s[:n]
	}

	// rawstring allocates storage for a new string. The returned
	// string and byte slice both refer to the same storage.
	// The storage is not zeroed. Callers should use
	// b to set the string contents and then drop b.
	func rawstring(size int) (s string, b []byte) {
	p := mallocgc(uintptr(size), nil, false)

	stringStructOf(&s).str = p
	stringStructOf(&s).len = size

	(slice)(unsafe.Pointer(&b)) = slice{p, size, size}

	return
	}

	// rawbyteslice allocates a new byte slice. The byte slice is not zeroed.
	func rawbyteslice(size int) (b []byte) {
	cap := roundupsize(uintptr(size))
	p := mallocgc(cap, nil, false)
	if cap != uintptr(size) {
	memclrNoHeapPointers(add(p, uintptr(size)), cap-uintptr(size))
	}

	(slice)(unsafe.Pointer(&b)) = slice{p, size, int(cap)}
	return
	}

	// rawruneslice allocates a new rune slice. The rune slice is not zeroed.
	func rawruneslice(size int) (b []rune) {
	if uintptr(size) > maxAlloc/4 {
	throw("out of memory")
	}
	mem := roundupsize(uintptr(size) * 4)
	p := mallocgc(mem, nil, false)
	if mem != uintptr(size)*4 {
	memclrNoHeapPointers(add(p, uintptr(size)4), mem-uintptr(size)4)
	}

	(slice)(unsafe.Pointer(&b)) = slice{p, size, int(mem / 4)}
	return
	}

	// used by cmd/cgo
	func gobytes(p *byte, n int) (b []byte) {
	if n == 0 {
	return make([]byte, 0)
	}

	if n < 0 \|\| uintptr(n) > maxAlloc {
	panic(errorString("gobytes: length out of range"))
	}

	bp := mallocgc(uintptr(n), nil, false)
	memmove(bp, unsafe.Pointer(p), uintptr(n))

	(slice)(unsafe.Pointer(&b)) = slice{bp, n, n}
	return
	}

	// This is exported via linkname to assembly in syscall (for Plan9).
	//go:linkname gostring
	func gostring(p *byte) string {
	l := findnull(p)
	if l == 0 {
	return ""
	}
	s, b := rawstring(l)
	memmove(unsafe.Pointer(&b[0]), unsafe.Pointer(p), uintptr(l))
	return s
	}

	func gostringn(p *byte, l int) string {
	if l == 0 {
	return ""
	}
	s, b := rawstring(l)
	memmove(unsafe.Pointer(&b[0]), unsafe.Pointer(p), uintptr(l))
	return s
	}

	func index(s, t string) int {
	if len(t) == 0 {
	return 0
	}
	for i := 0; i < len(s); i++ {
	if s[i] == t[0] && hasPrefix(s[i:], t) {
	return i
	}
	}
	return -1
	}

	func contains(s, t string) bool {
	return index(s, t) >= 0
	}

	func hasPrefix(s, prefix string) bool {
	return len(s) >= len(prefix) && s[:len(prefix)] == prefix
	}

	func hasSuffix(s, suffix string) bool {
	return len(s) >= len(suffix) && s[len(s)-len(suffix):] == suffix
	}

	const (
	maxUint = ^uint(0)
	maxInt = int(maxUint >> 1)
	)

	// atoi parses an int from a string s.
	// The bool result reports whether s is a number
	// representable by a value of type int.
	func atoi(s string) (int, bool) {
	if s == "" {
	return 0, false
	}

	neg := false
	if s[0] == '-' {
	neg = true
	s = s[1:]
	}

	un := uint(0)
	for i := 0; i < len(s); i++ {
	c := s[i]
	if c < '0' \|\| c > '9' {
	return 0, false
	}
	if un > maxUint/10 {
	// overflow
	return 0, false
	}
	un *= 10
	un1 := un + uint(c) - '0'
	if un1 < un {
	// overflow
	return 0, false
	}
	un = un1
	}

	if !neg && un > uint(maxInt) {
	return 0, false
	}
	if neg && un > uint(maxInt)+1 {
	return 0, false
	}

	n := int(un)
	if neg {
	n = -n
	}

	return n, true
	}

	// atoi32 is like atoi but for integers
	// that fit into an int32.
	func atoi32(s string) (int32, bool) {
	if n, ok := atoi(s); n == int(int32(n)) {
	return int32(n), ok
	}
	return 0, false
	}

	//go:nosplit
	func findnull(s *byte) int {
	if s == nil {
	return 0
	}

	// Avoid IndexByteString on Plan 9 because it uses SSE instructions
	// on x86 machines, and those are classified as floating point instructions,
	// which are illegal in a note handler.
	if GOOS == "plan9" {
	p := (*[maxAlloc/2 - 1]byte)(unsafe.Pointer(s))
	l := 0
	for p[l] != 0 {
	l++
	}
	return l
	}

	// pageSize is the unit we scan at a time looking for NULL.
	// It must be the minimum page size for any architecture Go
	// runs on. It's okay (just a minor performance loss) if the
	// actual system page size is larger than this value.
	const pageSize = 4096

	offset := 0
	ptr := unsafe.Pointer(s)
	// IndexByteString uses wide reads, so we need to be careful
	// with page boundaries. Call IndexByteString on
	// [ptr, endOfPage) interval.
	safeLen := int(pageSize - uintptr(ptr)%pageSize)

	for {
	t := (string)(unsafe.Pointer(&stringStruct{ptr, safeLen}))
	// Check one page at a time.
	if i := bytealg.IndexByteString(t, 0); i != -1 {
	return offset + i
	}
	// Move to next page
	ptr = unsafe.Pointer(uintptr(ptr) + uintptr(safeLen))
	offset += safeLen
	safeLen = pageSize
	}
	}

	func findnullw(s *uint16) int {
	if s == nil {
	return 0
	}
	p := (*[maxAlloc/2/2 - 1]uint16)(unsafe.Pointer(s))
	l := 0
	for p[l] != 0 {
	l++
	}
	return l
	}

	//go:nosplit
	func gostringnocopy(str *byte) string {
	ss := stringStruct{str: unsafe.Pointer(str), len: findnull(str)}
	s := (string)(unsafe.Pointer(&ss))
	return s
	}

	func gostringw(strw *uint16) string {
	var buf [8]byte
	str := (*[maxAlloc/2/2 - 1]uint16)(unsafe.Pointer(strw))
	n1 := 0
	for i := 0; str[i] != 0; i++ {
	n1 += encoderune(buf[:], rune(str[i]))
	}
	s, b := rawstring(n1 + 4)
	n2 := 0
	for i := 0; str[i] != 0; i++ {
	// check for race
	if n2 >= n1 {
	break
	}
	n2 += encoderune(b[n2:], rune(str[i]))
	}
	b[n2] = 0 // for luck
	return s[:n2]
	}

	// These two functions are called by code generated by cgo -gccgo.

	//go:linkname __go_byte_array_to_string __go_byte_array_to_string
	func __go_byte_array_to_string(p unsafe.Pointer, l int) string {
	if l == 0 {
	return ""
	}
	s, c := rawstringtmp(nil, l)
	memmove(unsafe.Pointer(&c[0]), p, uintptr(l))
	return s
	}

	//go:linkname __go_string_to_byte_array __go_string_to_byte_array
	func __go_string_to_byte_array(s string) []byte {
	return stringtoslicebyte(nil, s)
	}

	// parseRelease parses a dot-separated version number. It follows the
	// semver syntax, but allows the minor and patch versions to be
	// elided.
	func parseRelease(rel string) (major, minor, patch int, ok bool) {
	// Strip anything after a dash or plus.
	for i := 0; i < len(rel); i++ {
	if rel[i] == '-' \|\| rel[i] == '+' {
	rel = rel[:i]
	break
	}
	}

	next := func() (int, bool) {
	for i := 0; i < len(rel); i++ {
	if rel[i] == '.' {
	ver, ok := atoi(rel[:i])
	rel = rel[i+1:]
	return ver, ok
	}
	}
	ver, ok := atoi(rel)
	rel = ""
	return ver, ok
	}
	if major, ok = next(); !ok \|\| rel == "" {
	return
	}
	if minor, ok = next(); !ok \|\| rel == "" {
	return
	}
	patch, ok = next()
	return
	}