github.com/mh-cbon/go@v0.0.0-20160603070303-9e112a3fe4c0/src/runtime/string.go (about) 1 // Copyright 2014 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 package runtime 6 7 import ( 8 "runtime/internal/atomic" 9 "unsafe" 10 ) 11 12 // The constant is known to the compiler. 13 // There is no fundamental theory behind this number. 14 const tmpStringBufSize = 32 15 16 type tmpBuf [tmpStringBufSize]byte 17 18 // concatstrings implements a Go string concatenation x+y+z+... 19 // The operands are passed in the slice a. 20 // If buf != nil, the compiler has determined that the result does not 21 // escape the calling function, so the string data can be stored in buf 22 // if small enough. 23 func concatstrings(buf *tmpBuf, a []string) string { 24 idx := 0 25 l := 0 26 count := 0 27 for i, x := range a { 28 n := len(x) 29 if n == 0 { 30 continue 31 } 32 if l+n < l { 33 throw("string concatenation too long") 34 } 35 l += n 36 count++ 37 idx = i 38 } 39 if count == 0 { 40 return "" 41 } 42 43 // If there is just one string and either it is not on the stack 44 // or our result does not escape the calling frame (buf != nil), 45 // then we can return that string directly. 46 if count == 1 && (buf != nil || !stringDataOnStack(a[idx])) { 47 return a[idx] 48 } 49 s, b := rawstringtmp(buf, l) 50 l = 0 51 for _, x := range a { 52 copy(b[l:], x) 53 l += len(x) 54 } 55 return s 56 } 57 58 func concatstring2(buf *tmpBuf, a [2]string) string { 59 return concatstrings(buf, a[:]) 60 } 61 62 func concatstring3(buf *tmpBuf, a [3]string) string { 63 return concatstrings(buf, a[:]) 64 } 65 66 func concatstring4(buf *tmpBuf, a [4]string) string { 67 return concatstrings(buf, a[:]) 68 } 69 70 func concatstring5(buf *tmpBuf, a [5]string) string { 71 return concatstrings(buf, a[:]) 72 } 73 74 // Buf is a fixed-size buffer for the result, 75 // it is not nil if the result does not escape. 76 func slicebytetostring(buf *tmpBuf, b []byte) string { 77 l := len(b) 78 if l == 0 { 79 // Turns out to be a relatively common case. 80 // Consider that you want to parse out data between parens in "foo()bar", 81 // you find the indices and convert the subslice to string. 82 return "" 83 } 84 if raceenabled && l > 0 { 85 racereadrangepc(unsafe.Pointer(&b[0]), 86 uintptr(l), 87 getcallerpc(unsafe.Pointer(&buf)), 88 funcPC(slicebytetostring)) 89 } 90 if msanenabled && l > 0 { 91 msanread(unsafe.Pointer(&b[0]), uintptr(l)) 92 } 93 s, c := rawstringtmp(buf, l) 94 copy(c, b) 95 return s 96 } 97 98 // stringDataOnStack reports whether the string's data is 99 // stored on the current goroutine's stack. 100 func stringDataOnStack(s string) bool { 101 ptr := uintptr(stringStructOf(&s).str) 102 stk := getg().stack 103 return stk.lo <= ptr && ptr < stk.hi 104 } 105 106 func rawstringtmp(buf *tmpBuf, l int) (s string, b []byte) { 107 if buf != nil && l <= len(buf) { 108 b = buf[:l] 109 s = slicebytetostringtmp(b) 110 } else { 111 s, b = rawstring(l) 112 } 113 return 114 } 115 116 func slicebytetostringtmp(b []byte) string { 117 // Return a "string" referring to the actual []byte bytes. 118 // This is only for use by internal compiler optimizations 119 // that know that the string form will be discarded before 120 // the calling goroutine could possibly modify the original 121 // slice or synchronize with another goroutine. 122 // First such case is a m[string(k)] lookup where 123 // m is a string-keyed map and k is a []byte. 124 // Second such case is "<"+string(b)+">" concatenation where b is []byte. 125 // Third such case is string(b)=="foo" comparison where b is []byte. 126 127 if raceenabled && len(b) > 0 { 128 racereadrangepc(unsafe.Pointer(&b[0]), 129 uintptr(len(b)), 130 getcallerpc(unsafe.Pointer(&b)), 131 funcPC(slicebytetostringtmp)) 132 } 133 if msanenabled && len(b) > 0 { 134 msanread(unsafe.Pointer(&b[0]), uintptr(len(b))) 135 } 136 return *(*string)(unsafe.Pointer(&b)) 137 } 138 139 func stringtoslicebyte(buf *tmpBuf, s string) []byte { 140 var b []byte 141 if buf != nil && len(s) <= len(buf) { 142 *buf = tmpBuf{} 143 b = buf[:len(s)] 144 } else { 145 b = rawbyteslice(len(s)) 146 } 147 copy(b, s) 148 return b 149 } 150 151 func stringtoslicebytetmp(s string) []byte { 152 // Return a slice referring to the actual string bytes. 153 // This is only for use by internal compiler optimizations 154 // that know that the slice won't be mutated. 155 // The only such case today is: 156 // for i, c := range []byte(str) 157 158 str := stringStructOf(&s) 159 ret := slice{array: str.str, len: str.len, cap: str.len} 160 return *(*[]byte)(unsafe.Pointer(&ret)) 161 } 162 163 func stringtoslicerune(buf *[tmpStringBufSize]rune, s string) []rune { 164 // two passes. 165 // unlike slicerunetostring, no race because strings are immutable. 166 n := 0 167 t := s 168 for len(s) > 0 { 169 _, k := charntorune(s) 170 s = s[k:] 171 n++ 172 } 173 var a []rune 174 if buf != nil && n <= len(buf) { 175 *buf = [tmpStringBufSize]rune{} 176 a = buf[:n] 177 } else { 178 a = rawruneslice(n) 179 } 180 n = 0 181 for len(t) > 0 { 182 r, k := charntorune(t) 183 t = t[k:] 184 a[n] = r 185 n++ 186 } 187 return a 188 } 189 190 func slicerunetostring(buf *tmpBuf, a []rune) string { 191 if raceenabled && len(a) > 0 { 192 racereadrangepc(unsafe.Pointer(&a[0]), 193 uintptr(len(a))*unsafe.Sizeof(a[0]), 194 getcallerpc(unsafe.Pointer(&buf)), 195 funcPC(slicerunetostring)) 196 } 197 if msanenabled && len(a) > 0 { 198 msanread(unsafe.Pointer(&a[0]), uintptr(len(a))*unsafe.Sizeof(a[0])) 199 } 200 var dum [4]byte 201 size1 := 0 202 for _, r := range a { 203 size1 += runetochar(dum[:], r) 204 } 205 s, b := rawstringtmp(buf, size1+3) 206 size2 := 0 207 for _, r := range a { 208 // check for race 209 if size2 >= size1 { 210 break 211 } 212 size2 += runetochar(b[size2:], r) 213 } 214 return s[:size2] 215 } 216 217 type stringStruct struct { 218 str unsafe.Pointer 219 len int 220 } 221 222 // Variant with *byte pointer type for DWARF debugging. 223 type stringStructDWARF struct { 224 str *byte 225 len int 226 } 227 228 func stringStructOf(sp *string) *stringStruct { 229 return (*stringStruct)(unsafe.Pointer(sp)) 230 } 231 232 func intstring(buf *[4]byte, v int64) string { 233 var s string 234 var b []byte 235 if buf != nil { 236 b = buf[:] 237 s = slicebytetostringtmp(b) 238 } else { 239 s, b = rawstring(4) 240 } 241 if int64(rune(v)) != v { 242 v = runeerror 243 } 244 n := runetochar(b, rune(v)) 245 return s[:n] 246 } 247 248 // stringiter returns the index of the next 249 // rune after the rune that starts at s[k]. 250 func stringiter(s string, k int) int { 251 if k >= len(s) { 252 // 0 is end of iteration 253 return 0 254 } 255 256 c := s[k] 257 if c < runeself { 258 return k + 1 259 } 260 261 // multi-char rune 262 _, n := charntorune(s[k:]) 263 return k + n 264 } 265 266 // stringiter2 returns the rune that starts at s[k] 267 // and the index where the next rune starts. 268 func stringiter2(s string, k int) (int, rune) { 269 if k >= len(s) { 270 // 0 is end of iteration 271 return 0, 0 272 } 273 274 c := s[k] 275 if c < runeself { 276 return k + 1, rune(c) 277 } 278 279 // multi-char rune 280 r, n := charntorune(s[k:]) 281 return k + n, r 282 } 283 284 // rawstring allocates storage for a new string. The returned 285 // string and byte slice both refer to the same storage. 286 // The storage is not zeroed. Callers should use 287 // b to set the string contents and then drop b. 288 func rawstring(size int) (s string, b []byte) { 289 p := mallocgc(uintptr(size), nil, false) 290 291 stringStructOf(&s).str = p 292 stringStructOf(&s).len = size 293 294 *(*slice)(unsafe.Pointer(&b)) = slice{p, size, size} 295 296 for { 297 ms := maxstring 298 if uintptr(size) <= ms || atomic.Casuintptr((*uintptr)(unsafe.Pointer(&maxstring)), ms, uintptr(size)) { 299 return 300 } 301 } 302 } 303 304 // rawbyteslice allocates a new byte slice. The byte slice is not zeroed. 305 func rawbyteslice(size int) (b []byte) { 306 cap := roundupsize(uintptr(size)) 307 p := mallocgc(cap, nil, false) 308 if cap != uintptr(size) { 309 memclr(add(p, uintptr(size)), cap-uintptr(size)) 310 } 311 312 *(*slice)(unsafe.Pointer(&b)) = slice{p, size, int(cap)} 313 return 314 } 315 316 // rawruneslice allocates a new rune slice. The rune slice is not zeroed. 317 func rawruneslice(size int) (b []rune) { 318 if uintptr(size) > _MaxMem/4 { 319 throw("out of memory") 320 } 321 mem := roundupsize(uintptr(size) * 4) 322 p := mallocgc(mem, nil, false) 323 if mem != uintptr(size)*4 { 324 memclr(add(p, uintptr(size)*4), mem-uintptr(size)*4) 325 } 326 327 *(*slice)(unsafe.Pointer(&b)) = slice{p, size, int(mem / 4)} 328 return 329 } 330 331 // used by cmd/cgo 332 func gobytes(p *byte, n int) []byte { 333 if n == 0 { 334 return make([]byte, 0) 335 } 336 x := make([]byte, n) 337 memmove(unsafe.Pointer(&x[0]), unsafe.Pointer(p), uintptr(n)) 338 return x 339 } 340 341 func gostring(p *byte) string { 342 l := findnull(p) 343 if l == 0 { 344 return "" 345 } 346 s, b := rawstring(l) 347 memmove(unsafe.Pointer(&b[0]), unsafe.Pointer(p), uintptr(l)) 348 return s 349 } 350 351 func gostringn(p *byte, l int) string { 352 if l == 0 { 353 return "" 354 } 355 s, b := rawstring(l) 356 memmove(unsafe.Pointer(&b[0]), unsafe.Pointer(p), uintptr(l)) 357 return s 358 } 359 360 func index(s, t string) int { 361 if len(t) == 0 { 362 return 0 363 } 364 for i := 0; i < len(s); i++ { 365 if s[i] == t[0] && hasprefix(s[i:], t) { 366 return i 367 } 368 } 369 return -1 370 } 371 372 func contains(s, t string) bool { 373 return index(s, t) >= 0 374 } 375 376 func hasprefix(s, t string) bool { 377 return len(s) >= len(t) && s[:len(t)] == t 378 } 379 380 func atoi(s string) int { 381 n := 0 382 for len(s) > 0 && '0' <= s[0] && s[0] <= '9' { 383 n = n*10 + int(s[0]) - '0' 384 s = s[1:] 385 } 386 return n 387 } 388 389 //go:nosplit 390 func findnull(s *byte) int { 391 if s == nil { 392 return 0 393 } 394 p := (*[_MaxMem/2 - 1]byte)(unsafe.Pointer(s)) 395 l := 0 396 for p[l] != 0 { 397 l++ 398 } 399 return l 400 } 401 402 func findnullw(s *uint16) int { 403 if s == nil { 404 return 0 405 } 406 p := (*[_MaxMem/2/2 - 1]uint16)(unsafe.Pointer(s)) 407 l := 0 408 for p[l] != 0 { 409 l++ 410 } 411 return l 412 } 413 414 var maxstring uintptr = 256 // a hint for print 415 416 //go:nosplit 417 func gostringnocopy(str *byte) string { 418 ss := stringStruct{str: unsafe.Pointer(str), len: findnull(str)} 419 s := *(*string)(unsafe.Pointer(&ss)) 420 for { 421 ms := maxstring 422 if uintptr(len(s)) <= ms || atomic.Casuintptr(&maxstring, ms, uintptr(len(s))) { 423 break 424 } 425 } 426 return s 427 } 428 429 func gostringw(strw *uint16) string { 430 var buf [8]byte 431 str := (*[_MaxMem/2/2 - 1]uint16)(unsafe.Pointer(strw)) 432 n1 := 0 433 for i := 0; str[i] != 0; i++ { 434 n1 += runetochar(buf[:], rune(str[i])) 435 } 436 s, b := rawstring(n1 + 4) 437 n2 := 0 438 for i := 0; str[i] != 0; i++ { 439 // check for race 440 if n2 >= n1 { 441 break 442 } 443 n2 += runetochar(b[n2:], rune(str[i])) 444 } 445 b[n2] = 0 // for luck 446 return s[:n2] 447 }