// 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/abi"
"internal/bytealg"
"internal/goarch"
"unsafe"
)
// The constant is known to the compiler.
// There is no fundamental theory behind this number.
// 编译器知道该常量。这个数字背后没有根本的理论。
const tmpStringBufSize = 32
type tmpBuf [tmpStringBufSize]byte
// concatstrings implements a Go string concatenation x+y+z+...
// concatstrings实现Go字符串串联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.
// 操作数在切片a中传递。如果buf!=nil,编译器已确定结果不会转义调用函数,因此如果字符串数据足够小,则可以将其存储在buf中。
func concatstrings(buf *tmpBuf, a []string) string {
idx := 0
l := 0
count := 0
for i, 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.
// 如果只有一个字符串,或者它不在堆栈上,或者我们的结果没有转义调用帧(buf!=nil),那么我们可以直接返回该字符串。
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
}
func concatstring2(buf *tmpBuf, a0, a1 string) string {
return concatstrings(buf, []string{a0, a1})
}
func concatstring3(buf *tmpBuf, a0, a1, a2 string) string {
return concatstrings(buf, []string{a0, a1, a2})
}
func concatstring4(buf *tmpBuf, a0, a1, a2, a3 string) string {
return concatstrings(buf, []string{a0, a1, a2, a3})
}
func concatstring5(buf *tmpBuf, a0, a1, a2, a3, a4 string) string {
return concatstrings(buf, []string{a0, a1, a2, a3, a4})
}
// 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.
// slicebytetostring将字节切片转换为字符串。它由编译器插入到生成的代码中。ptr是指向切片的第一个元素的指针;n是切片的长度。
// Buf是一个固定大小的结果缓冲区,如果结果没有转义,它就不是零。
func slicebytetostring(buf *tmpBuf, ptr *byte, n int) 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(),
abi.FuncPCABIInternal(slicebytetostring))
}
if msanenabled {
msanread(unsafe.Pointer(ptr), uintptr(n))
}
if asanenabled {
asanread(unsafe.Pointer(ptr), uintptr(n))
}
if n == 1 {
p := unsafe.Pointer(&staticuint64s[*ptr])
if goarch.BigEndian {
p = add(p, 7)
}
return unsafe.String((*byte)(p), 1)
}
var p unsafe.Pointer
if buf != nil && n <= len(buf) {
p = unsafe.Pointer(buf)
} else {
p = mallocgc(uintptr(n), nil, false)
}
memmove(p, unsafe.Pointer(ptr), uintptr(n))
return unsafe.String((*byte)(p), n)
}
// stringDataOnStack reports whether the string's data is
// stored on the current goroutine's stack.
// stringDataOnStack报告字符串的数据是否存储在当前goroutine的堆栈上。
func stringDataOnStack(s string) bool {
ptr := uintptr(unsafe.Pointer(unsafe.StringData(s)))
stk := getg().stack
return stk.lo <= ptr && ptr < stk.hi
}
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.
// slicebytetostringtmp返回一个“字符串”,指的是实际的[]字节。
// 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.
// 调用方需要确保在调用goroutine修改原始切片或与另一个goroutine同步后不会使用返回的字符串。
// The function is only called when instrumenting
// and otherwise intrinsified by the compiler.
// 该函数仅在检测时调用,否则将由编译器内部化。
// 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) string {
if raceenabled && n > 0 {
racereadrangepc(unsafe.Pointer(ptr),
uintptr(n),
getcallerpc(),
abi.FuncPCABIInternal(slicebytetostringtmp))
}
if msanenabled && n > 0 {
msanread(unsafe.Pointer(ptr), uintptr(n))
}
if asanenabled && n > 0 {
asanread(unsafe.Pointer(ptr), uintptr(n))
}
return unsafe.String(ptr, n)
}
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.
// 与sliceruneostring不同,没有种族,因为字符串是不可变的。
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(),
abi.FuncPCABIInternal(slicerunetostring))
}
if msanenabled && len(a) > 0 {
msanread(unsafe.Pointer(&a[0]), uintptr(len(a))*unsafe.Sizeof(a[0]))
}
if asanenabled && len(a) > 0 {
asanread(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 // 字符串的首地址
len int // 字符串的长度
}
// Variant with *byte pointer type for DWARF debugging. 用于DWARF调试的具有*字节指针类型的变量。
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) {
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.
// rawstring为新字符串分配存储空间。返回的字符串和字节片都引用相同的存储。存储未归零。调用方应使用b设置字符串内容,然后删除b
func rawstring(size int) (s string, b []byte) {
p := mallocgc(uintptr(size), nil, false)
return unsafe.String((*byte)(p), size), unsafe.Slice((*byte)(p), size)
}
// rawbyteslice allocates a new byte slice. The byte slice is not zeroed.
// rawbyteslice分配一个新的字节片。字节片未归零。
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.
// rawruneslice分配一个新的rune切片。rune切片非零值。
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).
// 这是通过链接名导出到系统调用中的程序集(对于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
}
// internal_syscall_gostring is a version of gostring for internal/syscall/unix.
// internal_syscall_gostring是用于internal/syscall/unix的gostring版本。
//go:linkname internal_syscall_gostring internal/syscall/unix.gostring
func internal_syscall_gostring(p *byte) string {
return gostring(p)
}
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 hasPrefix(s, prefix string) bool {
return len(s) >= len(prefix) && s[:len(prefix)] == prefix
}
const (
maxUint64 = ^uint64(0)
maxInt64 = int64(maxUint64 >> 1)
)
// atoi64 parses an int64 from a string s.
// The bool result reports whether s is a number
// representable by a value of type int64.
// atoi64从字符串s中解析一个int64。布尔结果报告s是否是一个可以由类型为int64的值表示的数字。
func atoi64(s string) (int64, bool) {
if s == "" {
return 0, false
}
neg := false
if s[0] == '-' {
neg = true
s = s[1:]
}
un := uint64(0)
for i := 0; i < len(s); i++ {
c := s[i]
if c < '0' || c > '9' {
return 0, false
}
if un > maxUint64/10 {
// overflow
return 0, false
}
un *= 10
un1 := un + uint64(c) - '0'
if un1 < un {
// overflow
return 0, false
}
un = un1
}
if !neg && un > uint64(maxInt64) {
return 0, false
}
if neg && un > uint64(maxInt64)+1 {
return 0, false
}
n := int64(un)
if neg {
n = -n
}
return n, true
}
// atoi is like atoi64 but for integers
// that fit into an int.
// atoi类似于atoi64,但适用于整数。
func atoi(s string) (int, bool) {
if n, ok := atoi64(s); n == int64(int(n)) {
return int(n), ok
}
return 0, false
}
// atoi32 is like atoi but for integers
// that fit into an int32.
// atoi32类似于atoi,但适用于适合int32的整数。
func atoi32(s string) (int32, bool) {
if n, ok := atoi64(s); n == int64(int32(n)) {
return int32(n), ok
}
return 0, false
}
// parseByteCount parses a string that represents a count of bytes.
// parseByteCount解析表示字节计数的字符串。
// s must match the following regular expression:
// s必须与以下正则表达式匹配:
// ^[0-9]+(([KMGT]i)?B)?$
//
// In other words, an integer byte count with an optional unit
// suffix. Acceptable suffixes include one of
// - KiB, MiB, GiB, TiB which represent binary IEC/ISO 80000 units, or
// - B, which just represents bytes.
// 换句话说,一个带有可选单位后缀的整数字节计数。可接受的后缀包括KiB、MiB、GiB、TiB中的一个,表示二进制IEC/ISO 80000单位,或-B,仅表示字节。
// Returns an int64 because that's what its callers want and receive,
// but the result is always non-negative.
// 返回一个int64,因为这是它的调用者想要和接收的,但结果总是非负的。
func parseByteCount(s string) (int64, bool) {
// The empty string is not valid. 空字符串无效。
if s == "" {
return 0, false
}
// Handle the easy non-suffix case. 处理简单的无后缀情况。
last := s[len(s)-1]
if last >= '0' && last <= '9' {
n, ok := atoi64(s)
if !ok || n < 0 {
return 0, false
}
return n, ok
}
// Failing a trailing digit, this must always end in 'B'.
// Also at this point there must be at least one digit before
// that B.
// 如果出现尾随数字,则必须始终以“B”结尾。在这一点上,B之前必须至少有一个数字。
if last != 'B' || len(s) < 2 {
return 0, false
}
// The one before that must always be a digit or 'i'.
// 在此之前的一个必须始终是数字或“i”。
if c := s[len(s)-2]; c >= '0' && c <= '9' {
// Trivial 'B' suffix.
n, ok := atoi64(s[:len(s)-1])
if !ok || n < 0 {
return 0, false
}
return n, ok
} else if c != 'i' {
return 0, false
}
// Finally, we need at least 4 characters now, for the unit
// prefix and at least one digit.
// 最后,我们现在至少需要4个字符,用于单位前缀和至少一个数字。
if len(s) < 4 {
return 0, false
}
power := 0
switch s[len(s)-3] {
case 'K':
power = 1
case 'M':
power = 2
case 'G':
power = 3
case 'T':
power = 4
default:
// Invalid suffix.
return 0, false
}
m := uint64(1)
for i := 0; i < power; i++ {
m *= 1024
}
n, ok := atoi64(s[:len(s)-3])
if !ok || n < 0 {
return 0, false
}
un := uint64(n)
if un > maxUint64/m {
// Overflow.
return 0, false
}
un *= m
if un > uint64(maxInt64) {
// Overflow.
return 0, false
}
return int64(un), true
}
//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.
// 在Plan 9中避免使用IndexByteString,因为它在x86计算机上使用SSE指令,并且这些指令被归类为浮点指令,在注释处理程序中是非法的。
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.
// pageSize是我们一次扫描查找NULL的单位。它必须是Go运行的任何架构的最小页面大小。如果实际系统页面大小大于这个值,也没关系(只是轻微的性能损失)。
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.
// IndexByteString使用宽读取,因此我们需要小心页面边界。在[ptr,endOfPage)间隔调用IndexByteString。
safeLen := int(pageSize - uintptr(ptr)%pageSize)
for {
t := *(*string)(unsafe.Pointer(&stringStruct{ptr, safeLen}))
// Check one page at a time. 一次检查一页。
if i := bytealg.IndexByteString(t, 0); i != -1 {
return offset + i
}
// Move to next page 移动到下一页
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]
}
[Golang1.20 source code reading] runtime/string.go
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