Source file src/bytes/bytes.go

Documentation: bytes

		 1  // Copyright 2009 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 bytes implements functions for the manipulation of byte slices.
		 6  // It is analogous to the facilities of the strings package.
		 7  package bytes
		 8  
		 9  import (
		10  	"internal/bytealg"
		11  	"unicode"
		12  	"unicode/utf8"
		13  )
		14  
		15  // Equal reports whether a and b
		16  // are the same length and contain the same bytes.
		17  // A nil argument is equivalent to an empty slice.
		18  func Equal(a, b []byte) bool {
		19  	// Neither cmd/compile nor gccgo allocates for these string conversions.
		20  	return string(a) == string(b)
		21  }
		22  
		23  // Compare returns an integer comparing two byte slices lexicographically.
		24  // The result will be 0 if a==b, -1 if a < b, and +1 if a > b.
		25  // A nil argument is equivalent to an empty slice.
		26  func Compare(a, b []byte) int {
		27  	return bytealg.Compare(a, b)
		28  }
		29  
		30  // explode splits s into a slice of UTF-8 sequences, one per Unicode code point (still slices of bytes),
		31  // up to a maximum of n byte slices. Invalid UTF-8 sequences are chopped into individual bytes.
		32  func explode(s []byte, n int) [][]byte {
		33  	if n <= 0 {
		34  		n = len(s)
		35  	}
		36  	a := make([][]byte, n)
		37  	var size int
		38  	na := 0
		39  	for len(s) > 0 {
		40  		if na+1 >= n {
		41  			a[na] = s
		42  			na++
		43  			break
		44  		}
		45  		_, size = utf8.DecodeRune(s)
		46  		a[na] = s[0:size:size]
		47  		s = s[size:]
		48  		na++
		49  	}
		50  	return a[0:na]
		51  }
		52  
		53  // Count counts the number of non-overlapping instances of sep in s.
		54  // If sep is an empty slice, Count returns 1 + the number of UTF-8-encoded code points in s.
		55  func Count(s, sep []byte) int {
		56  	// special case
		57  	if len(sep) == 0 {
		58  		return utf8.RuneCount(s) + 1
		59  	}
		60  	if len(sep) == 1 {
		61  		return bytealg.Count(s, sep[0])
		62  	}
		63  	n := 0
		64  	for {
		65  		i := Index(s, sep)
		66  		if i == -1 {
		67  			return n
		68  		}
		69  		n++
		70  		s = s[i+len(sep):]
		71  	}
		72  }
		73  
		74  // Contains reports whether subslice is within b.
		75  func Contains(b, subslice []byte) bool {
		76  	return Index(b, subslice) != -1
		77  }
		78  
		79  // ContainsAny reports whether any of the UTF-8-encoded code points in chars are within b.
		80  func ContainsAny(b []byte, chars string) bool {
		81  	return IndexAny(b, chars) >= 0
		82  }
		83  
		84  // ContainsRune reports whether the rune is contained in the UTF-8-encoded byte slice b.
		85  func ContainsRune(b []byte, r rune) bool {
		86  	return IndexRune(b, r) >= 0
		87  }
		88  
		89  // IndexByte returns the index of the first instance of c in b, or -1 if c is not present in b.
		90  func IndexByte(b []byte, c byte) int {
		91  	return bytealg.IndexByte(b, c)
		92  }
		93  
		94  func indexBytePortable(s []byte, c byte) int {
		95  	for i, b := range s {
		96  		if b == c {
		97  			return i
		98  		}
		99  	}
	 100  	return -1
	 101  }
	 102  
	 103  // LastIndex returns the index of the last instance of sep in s, or -1 if sep is not present in s.
	 104  func LastIndex(s, sep []byte) int {
	 105  	n := len(sep)
	 106  	switch {
	 107  	case n == 0:
	 108  		return len(s)
	 109  	case n == 1:
	 110  		return LastIndexByte(s, sep[0])
	 111  	case n == len(s):
	 112  		if Equal(s, sep) {
	 113  			return 0
	 114  		}
	 115  		return -1
	 116  	case n > len(s):
	 117  		return -1
	 118  	}
	 119  	// Rabin-Karp search from the end of the string
	 120  	hashss, pow := bytealg.HashStrRevBytes(sep)
	 121  	last := len(s) - n
	 122  	var h uint32
	 123  	for i := len(s) - 1; i >= last; i-- {
	 124  		h = h*bytealg.PrimeRK + uint32(s[i])
	 125  	}
	 126  	if h == hashss && Equal(s[last:], sep) {
	 127  		return last
	 128  	}
	 129  	for i := last - 1; i >= 0; i-- {
	 130  		h *= bytealg.PrimeRK
	 131  		h += uint32(s[i])
	 132  		h -= pow * uint32(s[i+n])
	 133  		if h == hashss && Equal(s[i:i+n], sep) {
	 134  			return i
	 135  		}
	 136  	}
	 137  	return -1
	 138  }
	 139  
	 140  // LastIndexByte returns the index of the last instance of c in s, or -1 if c is not present in s.
	 141  func LastIndexByte(s []byte, c byte) int {
	 142  	for i := len(s) - 1; i >= 0; i-- {
	 143  		if s[i] == c {
	 144  			return i
	 145  		}
	 146  	}
	 147  	return -1
	 148  }
	 149  
	 150  // IndexRune interprets s as a sequence of UTF-8-encoded code points.
	 151  // It returns the byte index of the first occurrence in s of the given rune.
	 152  // It returns -1 if rune is not present in s.
	 153  // If r is utf8.RuneError, it returns the first instance of any
	 154  // invalid UTF-8 byte sequence.
	 155  func IndexRune(s []byte, r rune) int {
	 156  	switch {
	 157  	case 0 <= r && r < utf8.RuneSelf:
	 158  		return IndexByte(s, byte(r))
	 159  	case r == utf8.RuneError:
	 160  		for i := 0; i < len(s); {
	 161  			r1, n := utf8.DecodeRune(s[i:])
	 162  			if r1 == utf8.RuneError {
	 163  				return i
	 164  			}
	 165  			i += n
	 166  		}
	 167  		return -1
	 168  	case !utf8.ValidRune(r):
	 169  		return -1
	 170  	default:
	 171  		var b [utf8.UTFMax]byte
	 172  		n := utf8.EncodeRune(b[:], r)
	 173  		return Index(s, b[:n])
	 174  	}
	 175  }
	 176  
	 177  // IndexAny interprets s as a sequence of UTF-8-encoded Unicode code points.
	 178  // It returns the byte index of the first occurrence in s of any of the Unicode
	 179  // code points in chars. It returns -1 if chars is empty or if there is no code
	 180  // point in common.
	 181  func IndexAny(s []byte, chars string) int {
	 182  	if chars == "" {
	 183  		// Avoid scanning all of s.
	 184  		return -1
	 185  	}
	 186  	if len(s) == 1 {
	 187  		r := rune(s[0])
	 188  		if r >= utf8.RuneSelf {
	 189  			// search utf8.RuneError.
	 190  			for _, r = range chars {
	 191  				if r == utf8.RuneError {
	 192  					return 0
	 193  				}
	 194  			}
	 195  			return -1
	 196  		}
	 197  		if bytealg.IndexByteString(chars, s[0]) >= 0 {
	 198  			return 0
	 199  		}
	 200  		return -1
	 201  	}
	 202  	if len(chars) == 1 {
	 203  		r := rune(chars[0])
	 204  		if r >= utf8.RuneSelf {
	 205  			r = utf8.RuneError
	 206  		}
	 207  		return IndexRune(s, r)
	 208  	}
	 209  	if len(s) > 8 {
	 210  		if as, isASCII := makeASCIISet(chars); isASCII {
	 211  			for i, c := range s {
	 212  				if as.contains(c) {
	 213  					return i
	 214  				}
	 215  			}
	 216  			return -1
	 217  		}
	 218  	}
	 219  	var width int
	 220  	for i := 0; i < len(s); i += width {
	 221  		r := rune(s[i])
	 222  		if r < utf8.RuneSelf {
	 223  			if bytealg.IndexByteString(chars, s[i]) >= 0 {
	 224  				return i
	 225  			}
	 226  			width = 1
	 227  			continue
	 228  		}
	 229  		r, width = utf8.DecodeRune(s[i:])
	 230  		if r != utf8.RuneError {
	 231  			// r is 2 to 4 bytes
	 232  			if len(chars) == width {
	 233  				if chars == string(r) {
	 234  					return i
	 235  				}
	 236  				continue
	 237  			}
	 238  			// Use bytealg.IndexString for performance if available.
	 239  			if bytealg.MaxLen >= width {
	 240  				if bytealg.IndexString(chars, string(r)) >= 0 {
	 241  					return i
	 242  				}
	 243  				continue
	 244  			}
	 245  		}
	 246  		for _, ch := range chars {
	 247  			if r == ch {
	 248  				return i
	 249  			}
	 250  		}
	 251  	}
	 252  	return -1
	 253  }
	 254  
	 255  // LastIndexAny interprets s as a sequence of UTF-8-encoded Unicode code
	 256  // points. It returns the byte index of the last occurrence in s of any of
	 257  // the Unicode code points in chars. It returns -1 if chars is empty or if
	 258  // there is no code point in common.
	 259  func LastIndexAny(s []byte, chars string) int {
	 260  	if chars == "" {
	 261  		// Avoid scanning all of s.
	 262  		return -1
	 263  	}
	 264  	if len(s) > 8 {
	 265  		if as, isASCII := makeASCIISet(chars); isASCII {
	 266  			for i := len(s) - 1; i >= 0; i-- {
	 267  				if as.contains(s[i]) {
	 268  					return i
	 269  				}
	 270  			}
	 271  			return -1
	 272  		}
	 273  	}
	 274  	if len(s) == 1 {
	 275  		r := rune(s[0])
	 276  		if r >= utf8.RuneSelf {
	 277  			for _, r = range chars {
	 278  				if r == utf8.RuneError {
	 279  					return 0
	 280  				}
	 281  			}
	 282  			return -1
	 283  		}
	 284  		if bytealg.IndexByteString(chars, s[0]) >= 0 {
	 285  			return 0
	 286  		}
	 287  		return -1
	 288  	}
	 289  	if len(chars) == 1 {
	 290  		cr := rune(chars[0])
	 291  		if cr >= utf8.RuneSelf {
	 292  			cr = utf8.RuneError
	 293  		}
	 294  		for i := len(s); i > 0; {
	 295  			r, size := utf8.DecodeLastRune(s[:i])
	 296  			i -= size
	 297  			if r == cr {
	 298  				return i
	 299  			}
	 300  		}
	 301  		return -1
	 302  	}
	 303  	for i := len(s); i > 0; {
	 304  		r := rune(s[i-1])
	 305  		if r < utf8.RuneSelf {
	 306  			if bytealg.IndexByteString(chars, s[i-1]) >= 0 {
	 307  				return i - 1
	 308  			}
	 309  			i--
	 310  			continue
	 311  		}
	 312  		r, size := utf8.DecodeLastRune(s[:i])
	 313  		i -= size
	 314  		if r != utf8.RuneError {
	 315  			// r is 2 to 4 bytes
	 316  			if len(chars) == size {
	 317  				if chars == string(r) {
	 318  					return i
	 319  				}
	 320  				continue
	 321  			}
	 322  			// Use bytealg.IndexString for performance if available.
	 323  			if bytealg.MaxLen >= size {
	 324  				if bytealg.IndexString(chars, string(r)) >= 0 {
	 325  					return i
	 326  				}
	 327  				continue
	 328  			}
	 329  		}
	 330  		for _, ch := range chars {
	 331  			if r == ch {
	 332  				return i
	 333  			}
	 334  		}
	 335  	}
	 336  	return -1
	 337  }
	 338  
	 339  // Generic split: splits after each instance of sep,
	 340  // including sepSave bytes of sep in the subslices.
	 341  func genSplit(s, sep []byte, sepSave, n int) [][]byte {
	 342  	if n == 0 {
	 343  		return nil
	 344  	}
	 345  	if len(sep) == 0 {
	 346  		return explode(s, n)
	 347  	}
	 348  	if n < 0 {
	 349  		n = Count(s, sep) + 1
	 350  	}
	 351  
	 352  	a := make([][]byte, n)
	 353  	n--
	 354  	i := 0
	 355  	for i < n {
	 356  		m := Index(s, sep)
	 357  		if m < 0 {
	 358  			break
	 359  		}
	 360  		a[i] = s[: m+sepSave : m+sepSave]
	 361  		s = s[m+len(sep):]
	 362  		i++
	 363  	}
	 364  	a[i] = s
	 365  	return a[:i+1]
	 366  }
	 367  
	 368  // SplitN slices s into subslices separated by sep and returns a slice of
	 369  // the subslices between those separators.
	 370  // If sep is empty, SplitN splits after each UTF-8 sequence.
	 371  // The count determines the number of subslices to return:
	 372  //	 n > 0: at most n subslices; the last subslice will be the unsplit remainder.
	 373  //	 n == 0: the result is nil (zero subslices)
	 374  //	 n < 0: all subslices
	 375  func SplitN(s, sep []byte, n int) [][]byte { return genSplit(s, sep, 0, n) }
	 376  
	 377  // SplitAfterN slices s into subslices after each instance of sep and
	 378  // returns a slice of those subslices.
	 379  // If sep is empty, SplitAfterN splits after each UTF-8 sequence.
	 380  // The count determines the number of subslices to return:
	 381  //	 n > 0: at most n subslices; the last subslice will be the unsplit remainder.
	 382  //	 n == 0: the result is nil (zero subslices)
	 383  //	 n < 0: all subslices
	 384  func SplitAfterN(s, sep []byte, n int) [][]byte {
	 385  	return genSplit(s, sep, len(sep), n)
	 386  }
	 387  
	 388  // Split slices s into all subslices separated by sep and returns a slice of
	 389  // the subslices between those separators.
	 390  // If sep is empty, Split splits after each UTF-8 sequence.
	 391  // It is equivalent to SplitN with a count of -1.
	 392  func Split(s, sep []byte) [][]byte { return genSplit(s, sep, 0, -1) }
	 393  
	 394  // SplitAfter slices s into all subslices after each instance of sep and
	 395  // returns a slice of those subslices.
	 396  // If sep is empty, SplitAfter splits after each UTF-8 sequence.
	 397  // It is equivalent to SplitAfterN with a count of -1.
	 398  func SplitAfter(s, sep []byte) [][]byte {
	 399  	return genSplit(s, sep, len(sep), -1)
	 400  }
	 401  
	 402  var asciiSpace = [256]uint8{'\t': 1, '\n': 1, '\v': 1, '\f': 1, '\r': 1, ' ': 1}
	 403  
	 404  // Fields interprets s as a sequence of UTF-8-encoded code points.
	 405  // It splits the slice s around each instance of one or more consecutive white space
	 406  // characters, as defined by unicode.IsSpace, returning a slice of subslices of s or an
	 407  // empty slice if s contains only white space.
	 408  func Fields(s []byte) [][]byte {
	 409  	// First count the fields.
	 410  	// This is an exact count if s is ASCII, otherwise it is an approximation.
	 411  	n := 0
	 412  	wasSpace := 1
	 413  	// setBits is used to track which bits are set in the bytes of s.
	 414  	setBits := uint8(0)
	 415  	for i := 0; i < len(s); i++ {
	 416  		r := s[i]
	 417  		setBits |= r
	 418  		isSpace := int(asciiSpace[r])
	 419  		n += wasSpace & ^isSpace
	 420  		wasSpace = isSpace
	 421  	}
	 422  
	 423  	if setBits >= utf8.RuneSelf {
	 424  		// Some runes in the input slice are not ASCII.
	 425  		return FieldsFunc(s, unicode.IsSpace)
	 426  	}
	 427  
	 428  	// ASCII fast path
	 429  	a := make([][]byte, n)
	 430  	na := 0
	 431  	fieldStart := 0
	 432  	i := 0
	 433  	// Skip spaces in the front of the input.
	 434  	for i < len(s) && asciiSpace[s[i]] != 0 {
	 435  		i++
	 436  	}
	 437  	fieldStart = i
	 438  	for i < len(s) {
	 439  		if asciiSpace[s[i]] == 0 {
	 440  			i++
	 441  			continue
	 442  		}
	 443  		a[na] = s[fieldStart:i:i]
	 444  		na++
	 445  		i++
	 446  		// Skip spaces in between fields.
	 447  		for i < len(s) && asciiSpace[s[i]] != 0 {
	 448  			i++
	 449  		}
	 450  		fieldStart = i
	 451  	}
	 452  	if fieldStart < len(s) { // Last field might end at EOF.
	 453  		a[na] = s[fieldStart:len(s):len(s)]
	 454  	}
	 455  	return a
	 456  }
	 457  
	 458  // FieldsFunc interprets s as a sequence of UTF-8-encoded code points.
	 459  // It splits the slice s at each run of code points c satisfying f(c) and
	 460  // returns a slice of subslices of s. If all code points in s satisfy f(c), or
	 461  // len(s) == 0, an empty slice is returned.
	 462  //
	 463  // FieldsFunc makes no guarantees about the order in which it calls f(c)
	 464  // and assumes that f always returns the same value for a given c.
	 465  func FieldsFunc(s []byte, f func(rune) bool) [][]byte {
	 466  	// A span is used to record a slice of s of the form s[start:end].
	 467  	// The start index is inclusive and the end index is exclusive.
	 468  	type span struct {
	 469  		start int
	 470  		end	 int
	 471  	}
	 472  	spans := make([]span, 0, 32)
	 473  
	 474  	// Find the field start and end indices.
	 475  	// Doing this in a separate pass (rather than slicing the string s
	 476  	// and collecting the result substrings right away) is significantly
	 477  	// more efficient, possibly due to cache effects.
	 478  	start := -1 // valid span start if >= 0
	 479  	for i := 0; i < len(s); {
	 480  		size := 1
	 481  		r := rune(s[i])
	 482  		if r >= utf8.RuneSelf {
	 483  			r, size = utf8.DecodeRune(s[i:])
	 484  		}
	 485  		if f(r) {
	 486  			if start >= 0 {
	 487  				spans = append(spans, span{start, i})
	 488  				start = -1
	 489  			}
	 490  		} else {
	 491  			if start < 0 {
	 492  				start = i
	 493  			}
	 494  		}
	 495  		i += size
	 496  	}
	 497  
	 498  	// Last field might end at EOF.
	 499  	if start >= 0 {
	 500  		spans = append(spans, span{start, len(s)})
	 501  	}
	 502  
	 503  	// Create subslices from recorded field indices.
	 504  	a := make([][]byte, len(spans))
	 505  	for i, span := range spans {
	 506  		a[i] = s[span.start:span.end:span.end]
	 507  	}
	 508  
	 509  	return a
	 510  }
	 511  
	 512  // Join concatenates the elements of s to create a new byte slice. The separator
	 513  // sep is placed between elements in the resulting slice.
	 514  func Join(s [][]byte, sep []byte) []byte {
	 515  	if len(s) == 0 {
	 516  		return []byte{}
	 517  	}
	 518  	if len(s) == 1 {
	 519  		// Just return a copy.
	 520  		return append([]byte(nil), s[0]...)
	 521  	}
	 522  	n := len(sep) * (len(s) - 1)
	 523  	for _, v := range s {
	 524  		n += len(v)
	 525  	}
	 526  
	 527  	b := make([]byte, n)
	 528  	bp := copy(b, s[0])
	 529  	for _, v := range s[1:] {
	 530  		bp += copy(b[bp:], sep)
	 531  		bp += copy(b[bp:], v)
	 532  	}
	 533  	return b
	 534  }
	 535  
	 536  // HasPrefix tests whether the byte slice s begins with prefix.
	 537  func HasPrefix(s, prefix []byte) bool {
	 538  	return len(s) >= len(prefix) && Equal(s[0:len(prefix)], prefix)
	 539  }
	 540  
	 541  // HasSuffix tests whether the byte slice s ends with suffix.
	 542  func HasSuffix(s, suffix []byte) bool {
	 543  	return len(s) >= len(suffix) && Equal(s[len(s)-len(suffix):], suffix)
	 544  }
	 545  
	 546  // Map returns a copy of the byte slice s with all its characters modified
	 547  // according to the mapping function. If mapping returns a negative value, the character is
	 548  // dropped from the byte slice with no replacement. The characters in s and the
	 549  // output are interpreted as UTF-8-encoded code points.
	 550  func Map(mapping func(r rune) rune, s []byte) []byte {
	 551  	// In the worst case, the slice can grow when mapped, making
	 552  	// things unpleasant. But it's so rare we barge in assuming it's
	 553  	// fine. It could also shrink but that falls out naturally.
	 554  	maxbytes := len(s) // length of b
	 555  	nbytes := 0				// number of bytes encoded in b
	 556  	b := make([]byte, maxbytes)
	 557  	for i := 0; i < len(s); {
	 558  		wid := 1
	 559  		r := rune(s[i])
	 560  		if r >= utf8.RuneSelf {
	 561  			r, wid = utf8.DecodeRune(s[i:])
	 562  		}
	 563  		r = mapping(r)
	 564  		if r >= 0 {
	 565  			rl := utf8.RuneLen(r)
	 566  			if rl < 0 {
	 567  				rl = len(string(utf8.RuneError))
	 568  			}
	 569  			if nbytes+rl > maxbytes {
	 570  				// Grow the buffer.
	 571  				maxbytes = maxbytes*2 + utf8.UTFMax
	 572  				nb := make([]byte, maxbytes)
	 573  				copy(nb, b[0:nbytes])
	 574  				b = nb
	 575  			}
	 576  			nbytes += utf8.EncodeRune(b[nbytes:maxbytes], r)
	 577  		}
	 578  		i += wid
	 579  	}
	 580  	return b[0:nbytes]
	 581  }
	 582  
	 583  // Repeat returns a new byte slice consisting of count copies of b.
	 584  //
	 585  // It panics if count is negative or if
	 586  // the result of (len(b) * count) overflows.
	 587  func Repeat(b []byte, count int) []byte {
	 588  	if count == 0 {
	 589  		return []byte{}
	 590  	}
	 591  	// Since we cannot return an error on overflow,
	 592  	// we should panic if the repeat will generate
	 593  	// an overflow.
	 594  	// See Issue golang.org/issue/16237.
	 595  	if count < 0 {
	 596  		panic("bytes: negative Repeat count")
	 597  	} else if len(b)*count/count != len(b) {
	 598  		panic("bytes: Repeat count causes overflow")
	 599  	}
	 600  
	 601  	nb := make([]byte, len(b)*count)
	 602  	bp := copy(nb, b)
	 603  	for bp < len(nb) {
	 604  		copy(nb[bp:], nb[:bp])
	 605  		bp *= 2
	 606  	}
	 607  	return nb
	 608  }
	 609  
	 610  // ToUpper returns a copy of the byte slice s with all Unicode letters mapped to
	 611  // their upper case.
	 612  func ToUpper(s []byte) []byte {
	 613  	isASCII, hasLower := true, false
	 614  	for i := 0; i < len(s); i++ {
	 615  		c := s[i]
	 616  		if c >= utf8.RuneSelf {
	 617  			isASCII = false
	 618  			break
	 619  		}
	 620  		hasLower = hasLower || ('a' <= c && c <= 'z')
	 621  	}
	 622  
	 623  	if isASCII { // optimize for ASCII-only byte slices.
	 624  		if !hasLower {
	 625  			// Just return a copy.
	 626  			return append([]byte(""), s...)
	 627  		}
	 628  		b := make([]byte, len(s))
	 629  		for i := 0; i < len(s); i++ {
	 630  			c := s[i]
	 631  			if 'a' <= c && c <= 'z' {
	 632  				c -= 'a' - 'A'
	 633  			}
	 634  			b[i] = c
	 635  		}
	 636  		return b
	 637  	}
	 638  	return Map(unicode.ToUpper, s)
	 639  }
	 640  
	 641  // ToLower returns a copy of the byte slice s with all Unicode letters mapped to
	 642  // their lower case.
	 643  func ToLower(s []byte) []byte {
	 644  	isASCII, hasUpper := true, false
	 645  	for i := 0; i < len(s); i++ {
	 646  		c := s[i]
	 647  		if c >= utf8.RuneSelf {
	 648  			isASCII = false
	 649  			break
	 650  		}
	 651  		hasUpper = hasUpper || ('A' <= c && c <= 'Z')
	 652  	}
	 653  
	 654  	if isASCII { // optimize for ASCII-only byte slices.
	 655  		if !hasUpper {
	 656  			return append([]byte(""), s...)
	 657  		}
	 658  		b := make([]byte, len(s))
	 659  		for i := 0; i < len(s); i++ {
	 660  			c := s[i]
	 661  			if 'A' <= c && c <= 'Z' {
	 662  				c += 'a' - 'A'
	 663  			}
	 664  			b[i] = c
	 665  		}
	 666  		return b
	 667  	}
	 668  	return Map(unicode.ToLower, s)
	 669  }
	 670  
	 671  // ToTitle treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters mapped to their title case.
	 672  func ToTitle(s []byte) []byte { return Map(unicode.ToTitle, s) }
	 673  
	 674  // ToUpperSpecial treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters mapped to their
	 675  // upper case, giving priority to the special casing rules.
	 676  func ToUpperSpecial(c unicode.SpecialCase, s []byte) []byte {
	 677  	return Map(c.ToUpper, s)
	 678  }
	 679  
	 680  // ToLowerSpecial treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters mapped to their
	 681  // lower case, giving priority to the special casing rules.
	 682  func ToLowerSpecial(c unicode.SpecialCase, s []byte) []byte {
	 683  	return Map(c.ToLower, s)
	 684  }
	 685  
	 686  // ToTitleSpecial treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters mapped to their
	 687  // title case, giving priority to the special casing rules.
	 688  func ToTitleSpecial(c unicode.SpecialCase, s []byte) []byte {
	 689  	return Map(c.ToTitle, s)
	 690  }
	 691  
	 692  // ToValidUTF8 treats s as UTF-8-encoded bytes and returns a copy with each run of bytes
	 693  // representing invalid UTF-8 replaced with the bytes in replacement, which may be empty.
	 694  func ToValidUTF8(s, replacement []byte) []byte {
	 695  	b := make([]byte, 0, len(s)+len(replacement))
	 696  	invalid := false // previous byte was from an invalid UTF-8 sequence
	 697  	for i := 0; i < len(s); {
	 698  		c := s[i]
	 699  		if c < utf8.RuneSelf {
	 700  			i++
	 701  			invalid = false
	 702  			b = append(b, byte(c))
	 703  			continue
	 704  		}
	 705  		_, wid := utf8.DecodeRune(s[i:])
	 706  		if wid == 1 {
	 707  			i++
	 708  			if !invalid {
	 709  				invalid = true
	 710  				b = append(b, replacement...)
	 711  			}
	 712  			continue
	 713  		}
	 714  		invalid = false
	 715  		b = append(b, s[i:i+wid]...)
	 716  		i += wid
	 717  	}
	 718  	return b
	 719  }
	 720  
	 721  // isSeparator reports whether the rune could mark a word boundary.
	 722  // TODO: update when package unicode captures more of the properties.
	 723  func isSeparator(r rune) bool {
	 724  	// ASCII alphanumerics and underscore are not separators
	 725  	if r <= 0x7F {
	 726  		switch {
	 727  		case '0' <= r && r <= '9':
	 728  			return false
	 729  		case 'a' <= r && r <= 'z':
	 730  			return false
	 731  		case 'A' <= r && r <= 'Z':
	 732  			return false
	 733  		case r == '_':
	 734  			return false
	 735  		}
	 736  		return true
	 737  	}
	 738  	// Letters and digits are not separators
	 739  	if unicode.IsLetter(r) || unicode.IsDigit(r) {
	 740  		return false
	 741  	}
	 742  	// Otherwise, all we can do for now is treat spaces as separators.
	 743  	return unicode.IsSpace(r)
	 744  }
	 745  
	 746  // Title treats s as UTF-8-encoded bytes and returns a copy with all Unicode letters that begin
	 747  // words mapped to their title case.
	 748  //
	 749  // BUG(rsc): The rule Title uses for word boundaries does not handle Unicode punctuation properly.
	 750  func Title(s []byte) []byte {
	 751  	// Use a closure here to remember state.
	 752  	// Hackish but effective. Depends on Map scanning in order and calling
	 753  	// the closure once per rune.
	 754  	prev := ' '
	 755  	return Map(
	 756  		func(r rune) rune {
	 757  			if isSeparator(prev) {
	 758  				prev = r
	 759  				return unicode.ToTitle(r)
	 760  			}
	 761  			prev = r
	 762  			return r
	 763  		},
	 764  		s)
	 765  }
	 766  
	 767  // TrimLeftFunc treats s as UTF-8-encoded bytes and returns a subslice of s by slicing off
	 768  // all leading UTF-8-encoded code points c that satisfy f(c).
	 769  func TrimLeftFunc(s []byte, f func(r rune) bool) []byte {
	 770  	i := indexFunc(s, f, false)
	 771  	if i == -1 {
	 772  		return nil
	 773  	}
	 774  	return s[i:]
	 775  }
	 776  
	 777  // TrimRightFunc returns a subslice of s by slicing off all trailing
	 778  // UTF-8-encoded code points c that satisfy f(c).
	 779  func TrimRightFunc(s []byte, f func(r rune) bool) []byte {
	 780  	i := lastIndexFunc(s, f, false)
	 781  	if i >= 0 && s[i] >= utf8.RuneSelf {
	 782  		_, wid := utf8.DecodeRune(s[i:])
	 783  		i += wid
	 784  	} else {
	 785  		i++
	 786  	}
	 787  	return s[0:i]
	 788  }
	 789  
	 790  // TrimFunc returns a subslice of s by slicing off all leading and trailing
	 791  // UTF-8-encoded code points c that satisfy f(c).
	 792  func TrimFunc(s []byte, f func(r rune) bool) []byte {
	 793  	return TrimRightFunc(TrimLeftFunc(s, f), f)
	 794  }
	 795  
	 796  // TrimPrefix returns s without the provided leading prefix string.
	 797  // If s doesn't start with prefix, s is returned unchanged.
	 798  func TrimPrefix(s, prefix []byte) []byte {
	 799  	if HasPrefix(s, prefix) {
	 800  		return s[len(prefix):]
	 801  	}
	 802  	return s
	 803  }
	 804  
	 805  // TrimSuffix returns s without the provided trailing suffix string.
	 806  // If s doesn't end with suffix, s is returned unchanged.
	 807  func TrimSuffix(s, suffix []byte) []byte {
	 808  	if HasSuffix(s, suffix) {
	 809  		return s[:len(s)-len(suffix)]
	 810  	}
	 811  	return s
	 812  }
	 813  
	 814  // IndexFunc interprets s as a sequence of UTF-8-encoded code points.
	 815  // It returns the byte index in s of the first Unicode
	 816  // code point satisfying f(c), or -1 if none do.
	 817  func IndexFunc(s []byte, f func(r rune) bool) int {
	 818  	return indexFunc(s, f, true)
	 819  }
	 820  
	 821  // LastIndexFunc interprets s as a sequence of UTF-8-encoded code points.
	 822  // It returns the byte index in s of the last Unicode
	 823  // code point satisfying f(c), or -1 if none do.
	 824  func LastIndexFunc(s []byte, f func(r rune) bool) int {
	 825  	return lastIndexFunc(s, f, true)
	 826  }
	 827  
	 828  // indexFunc is the same as IndexFunc except that if
	 829  // truth==false, the sense of the predicate function is
	 830  // inverted.
	 831  func indexFunc(s []byte, f func(r rune) bool, truth bool) int {
	 832  	start := 0
	 833  	for start < len(s) {
	 834  		wid := 1
	 835  		r := rune(s[start])
	 836  		if r >= utf8.RuneSelf {
	 837  			r, wid = utf8.DecodeRune(s[start:])
	 838  		}
	 839  		if f(r) == truth {
	 840  			return start
	 841  		}
	 842  		start += wid
	 843  	}
	 844  	return -1
	 845  }
	 846  
	 847  // lastIndexFunc is the same as LastIndexFunc except that if
	 848  // truth==false, the sense of the predicate function is
	 849  // inverted.
	 850  func lastIndexFunc(s []byte, f func(r rune) bool, truth bool) int {
	 851  	for i := len(s); i > 0; {
	 852  		r, size := rune(s[i-1]), 1
	 853  		if r >= utf8.RuneSelf {
	 854  			r, size = utf8.DecodeLastRune(s[0:i])
	 855  		}
	 856  		i -= size
	 857  		if f(r) == truth {
	 858  			return i
	 859  		}
	 860  	}
	 861  	return -1
	 862  }
	 863  
	 864  // asciiSet is a 32-byte value, where each bit represents the presence of a
	 865  // given ASCII character in the set. The 128-bits of the lower 16 bytes,
	 866  // starting with the least-significant bit of the lowest word to the
	 867  // most-significant bit of the highest word, map to the full range of all
	 868  // 128 ASCII characters. The 128-bits of the upper 16 bytes will be zeroed,
	 869  // ensuring that any non-ASCII character will be reported as not in the set.
	 870  type asciiSet [8]uint32
	 871  
	 872  // makeASCIISet creates a set of ASCII characters and reports whether all
	 873  // characters in chars are ASCII.
	 874  func makeASCIISet(chars string) (as asciiSet, ok bool) {
	 875  	for i := 0; i < len(chars); i++ {
	 876  		c := chars[i]
	 877  		if c >= utf8.RuneSelf {
	 878  			return as, false
	 879  		}
	 880  		as[c>>5] |= 1 << uint(c&31)
	 881  	}
	 882  	return as, true
	 883  }
	 884  
	 885  // contains reports whether c is inside the set.
	 886  func (as *asciiSet) contains(c byte) bool {
	 887  	return (as[c>>5] & (1 << uint(c&31))) != 0
	 888  }
	 889  
	 890  func makeCutsetFunc(cutset string) func(r rune) bool {
	 891  	if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
	 892  		return func(r rune) bool {
	 893  			return r == rune(cutset[0])
	 894  		}
	 895  	}
	 896  	if as, isASCII := makeASCIISet(cutset); isASCII {
	 897  		return func(r rune) bool {
	 898  			return r < utf8.RuneSelf && as.contains(byte(r))
	 899  		}
	 900  	}
	 901  	return func(r rune) bool {
	 902  		for _, c := range cutset {
	 903  			if c == r {
	 904  				return true
	 905  			}
	 906  		}
	 907  		return false
	 908  	}
	 909  }
	 910  
	 911  // Trim returns a subslice of s by slicing off all leading and
	 912  // trailing UTF-8-encoded code points contained in cutset.
	 913  func Trim(s []byte, cutset string) []byte {
	 914  	return TrimFunc(s, makeCutsetFunc(cutset))
	 915  }
	 916  
	 917  // TrimLeft returns a subslice of s by slicing off all leading
	 918  // UTF-8-encoded code points contained in cutset.
	 919  func TrimLeft(s []byte, cutset string) []byte {
	 920  	return TrimLeftFunc(s, makeCutsetFunc(cutset))
	 921  }
	 922  
	 923  // TrimRight returns a subslice of s by slicing off all trailing
	 924  // UTF-8-encoded code points that are contained in cutset.
	 925  func TrimRight(s []byte, cutset string) []byte {
	 926  	return TrimRightFunc(s, makeCutsetFunc(cutset))
	 927  }
	 928  
	 929  // TrimSpace returns a subslice of s by slicing off all leading and
	 930  // trailing white space, as defined by Unicode.
	 931  func TrimSpace(s []byte) []byte {
	 932  	// Fast path for ASCII: look for the first ASCII non-space byte
	 933  	start := 0
	 934  	for ; start < len(s); start++ {
	 935  		c := s[start]
	 936  		if c >= utf8.RuneSelf {
	 937  			// If we run into a non-ASCII byte, fall back to the
	 938  			// slower unicode-aware method on the remaining bytes
	 939  			return TrimFunc(s[start:], unicode.IsSpace)
	 940  		}
	 941  		if asciiSpace[c] == 0 {
	 942  			break
	 943  		}
	 944  	}
	 945  
	 946  	// Now look for the first ASCII non-space byte from the end
	 947  	stop := len(s)
	 948  	for ; stop > start; stop-- {
	 949  		c := s[stop-1]
	 950  		if c >= utf8.RuneSelf {
	 951  			return TrimFunc(s[start:stop], unicode.IsSpace)
	 952  		}
	 953  		if asciiSpace[c] == 0 {
	 954  			break
	 955  		}
	 956  	}
	 957  
	 958  	// At this point s[start:stop] starts and ends with an ASCII
	 959  	// non-space bytes, so we're done. Non-ASCII cases have already
	 960  	// been handled above.
	 961  	if start == stop {
	 962  		// Special case to preserve previous TrimLeftFunc behavior,
	 963  		// returning nil instead of empty slice if all spaces.
	 964  		return nil
	 965  	}
	 966  	return s[start:stop]
	 967  }
	 968  
	 969  // Runes interprets s as a sequence of UTF-8-encoded code points.
	 970  // It returns a slice of runes (Unicode code points) equivalent to s.
	 971  func Runes(s []byte) []rune {
	 972  	t := make([]rune, utf8.RuneCount(s))
	 973  	i := 0
	 974  	for len(s) > 0 {
	 975  		r, l := utf8.DecodeRune(s)
	 976  		t[i] = r
	 977  		i++
	 978  		s = s[l:]
	 979  	}
	 980  	return t
	 981  }
	 982  
	 983  // Replace returns a copy of the slice s with the first n
	 984  // non-overlapping instances of old replaced by new.
	 985  // If old is empty, it matches at the beginning of the slice
	 986  // and after each UTF-8 sequence, yielding up to k+1 replacements
	 987  // for a k-rune slice.
	 988  // If n < 0, there is no limit on the number of replacements.
	 989  func Replace(s, old, new []byte, n int) []byte {
	 990  	m := 0
	 991  	if n != 0 {
	 992  		// Compute number of replacements.
	 993  		m = Count(s, old)
	 994  	}
	 995  	if m == 0 {
	 996  		// Just return a copy.
	 997  		return append([]byte(nil), s...)
	 998  	}
	 999  	if n < 0 || m < n {
	1000  		n = m
	1001  	}
	1002  
	1003  	// Apply replacements to buffer.
	1004  	t := make([]byte, len(s)+n*(len(new)-len(old)))
	1005  	w := 0
	1006  	start := 0
	1007  	for i := 0; i < n; i++ {
	1008  		j := start
	1009  		if len(old) == 0 {
	1010  			if i > 0 {
	1011  				_, wid := utf8.DecodeRune(s[start:])
	1012  				j += wid
	1013  			}
	1014  		} else {
	1015  			j += Index(s[start:], old)
	1016  		}
	1017  		w += copy(t[w:], s[start:j])
	1018  		w += copy(t[w:], new)
	1019  		start = j + len(old)
	1020  	}
	1021  	w += copy(t[w:], s[start:])
	1022  	return t[0:w]
	1023  }
	1024  
	1025  // ReplaceAll returns a copy of the slice s with all
	1026  // non-overlapping instances of old replaced by new.
	1027  // If old is empty, it matches at the beginning of the slice
	1028  // and after each UTF-8 sequence, yielding up to k+1 replacements
	1029  // for a k-rune slice.
	1030  func ReplaceAll(s, old, new []byte) []byte {
	1031  	return Replace(s, old, new, -1)
	1032  }
	1033  
	1034  // EqualFold reports whether s and t, interpreted as UTF-8 strings,
	1035  // are equal under Unicode case-folding, which is a more general
	1036  // form of case-insensitivity.
	1037  func EqualFold(s, t []byte) bool {
	1038  	for len(s) != 0 && len(t) != 0 {
	1039  		// Extract first rune from each.
	1040  		var sr, tr rune
	1041  		if s[0] < utf8.RuneSelf {
	1042  			sr, s = rune(s[0]), s[1:]
	1043  		} else {
	1044  			r, size := utf8.DecodeRune(s)
	1045  			sr, s = r, s[size:]
	1046  		}
	1047  		if t[0] < utf8.RuneSelf {
	1048  			tr, t = rune(t[0]), t[1:]
	1049  		} else {
	1050  			r, size := utf8.DecodeRune(t)
	1051  			tr, t = r, t[size:]
	1052  		}
	1053  
	1054  		// If they match, keep going; if not, return false.
	1055  
	1056  		// Easy case.
	1057  		if tr == sr {
	1058  			continue
	1059  		}
	1060  
	1061  		// Make sr < tr to simplify what follows.
	1062  		if tr < sr {
	1063  			tr, sr = sr, tr
	1064  		}
	1065  		// Fast check for ASCII.
	1066  		if tr < utf8.RuneSelf {
	1067  			// ASCII only, sr/tr must be upper/lower case
	1068  			if 'A' <= sr && sr <= 'Z' && tr == sr+'a'-'A' {
	1069  				continue
	1070  			}
	1071  			return false
	1072  		}
	1073  
	1074  		// General case. SimpleFold(x) returns the next equivalent rune > x
	1075  		// or wraps around to smaller values.
	1076  		r := unicode.SimpleFold(sr)
	1077  		for r != sr && r < tr {
	1078  			r = unicode.SimpleFold(r)
	1079  		}
	1080  		if r == tr {
	1081  			continue
	1082  		}
	1083  		return false
	1084  	}
	1085  
	1086  	// One string is empty. Are both?
	1087  	return len(s) == len(t)
	1088  }
	1089  
	1090  // Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
	1091  func Index(s, sep []byte) int {
	1092  	n := len(sep)
	1093  	switch {
	1094  	case n == 0:
	1095  		return 0
	1096  	case n == 1:
	1097  		return IndexByte(s, sep[0])
	1098  	case n == len(s):
	1099  		if Equal(sep, s) {
	1100  			return 0
	1101  		}
	1102  		return -1
	1103  	case n > len(s):
	1104  		return -1
	1105  	case n <= bytealg.MaxLen:
	1106  		// Use brute force when s and sep both are small
	1107  		if len(s) <= bytealg.MaxBruteForce {
	1108  			return bytealg.Index(s, sep)
	1109  		}
	1110  		c0 := sep[0]
	1111  		c1 := sep[1]
	1112  		i := 0
	1113  		t := len(s) - n + 1
	1114  		fails := 0
	1115  		for i < t {
	1116  			if s[i] != c0 {
	1117  				// IndexByte is faster than bytealg.Index, so use it as long as
	1118  				// we're not getting lots of false positives.
	1119  				o := IndexByte(s[i+1:t], c0)
	1120  				if o < 0 {
	1121  					return -1
	1122  				}
	1123  				i += o + 1
	1124  			}
	1125  			if s[i+1] == c1 && Equal(s[i:i+n], sep) {
	1126  				return i
	1127  			}
	1128  			fails++
	1129  			i++
	1130  			// Switch to bytealg.Index when IndexByte produces too many false positives.
	1131  			if fails > bytealg.Cutover(i) {
	1132  				r := bytealg.Index(s[i:], sep)
	1133  				if r >= 0 {
	1134  					return r + i
	1135  				}
	1136  				return -1
	1137  			}
	1138  		}
	1139  		return -1
	1140  	}
	1141  	c0 := sep[0]
	1142  	c1 := sep[1]
	1143  	i := 0
	1144  	fails := 0
	1145  	t := len(s) - n + 1
	1146  	for i < t {
	1147  		if s[i] != c0 {
	1148  			o := IndexByte(s[i+1:t], c0)
	1149  			if o < 0 {
	1150  				break
	1151  			}
	1152  			i += o + 1
	1153  		}
	1154  		if s[i+1] == c1 && Equal(s[i:i+n], sep) {
	1155  			return i
	1156  		}
	1157  		i++
	1158  		fails++
	1159  		if fails >= 4+i>>4 && i < t {
	1160  			// Give up on IndexByte, it isn't skipping ahead
	1161  			// far enough to be better than Rabin-Karp.
	1162  			// Experiments (using IndexPeriodic) suggest
	1163  			// the cutover is about 16 byte skips.
	1164  			// TODO: if large prefixes of sep are matching
	1165  			// we should cutover at even larger average skips,
	1166  			// because Equal becomes that much more expensive.
	1167  			// This code does not take that effect into account.
	1168  			j := bytealg.IndexRabinKarpBytes(s[i:], sep)
	1169  			if j < 0 {
	1170  				return -1
	1171  			}
	1172  			return i + j
	1173  		}
	1174  	}
	1175  	return -1
	1176  }
	1177  

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