github.com/likebike/go--@v0.0.0-20190911215757-0bd925d16e96/go/src/bytes/bytes_generic.go (about)

     1  // Copyright 2015 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  // +build !amd64,!s390x,!arm64
     6  
     7  package bytes
     8  
     9  // Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
    10  func Index(s, sep []byte) int {
    11  	n := len(sep)
    12  	switch {
    13  	case n == 0:
    14  		return 0
    15  	case n == 1:
    16  		return IndexByte(s, sep[0])
    17  	case n == len(s):
    18  		if Equal(sep, s) {
    19  			return 0
    20  		}
    21  		return -1
    22  	case n > len(s):
    23  		return -1
    24  	}
    25  	c := sep[0]
    26  	i := 0
    27  	fails := 0
    28  	t := s[:len(s)-n+1]
    29  	for i < len(t) {
    30  		if t[i] != c {
    31  			o := IndexByte(t[i:], c)
    32  			if o < 0 {
    33  				break
    34  			}
    35  			i += o
    36  		}
    37  		if Equal(s[i:i+n], sep) {
    38  			return i
    39  		}
    40  		i++
    41  		fails++
    42  		if fails >= 4+i>>4 && i < len(t) {
    43  			// Give up on IndexByte, it isn't skipping ahead
    44  			// far enough to be better than Rabin-Karp.
    45  			// Experiments (using IndexPeriodic) suggest
    46  			// the cutover is about 16 byte skips.
    47  			// TODO: if large prefixes of sep are matching
    48  			// we should cutover at even larger average skips,
    49  			// because Equal becomes that much more expensive.
    50  			// This code does not take that effect into account.
    51  			j := indexRabinKarp(s[i:], sep)
    52  			if j < 0 {
    53  				return -1
    54  			}
    55  			return i + j
    56  		}
    57  	}
    58  	return -1
    59  }
    60  
    61  // Count counts the number of non-overlapping instances of sep in s.
    62  // If sep is an empty slice, Count returns 1 + the number of UTF-8-encoded code points in s.
    63  func Count(s, sep []byte) int {
    64  	return countGeneric(s, sep)
    65  }