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Source file src/bytes/bytes_generic.go

Documentation: bytes

  // Copyright 2015 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.
  
  // +build !amd64,!s390x,!arm64
  
  package bytes
  
  // Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
  func Index(s, sep []byte) int {
  	n := len(sep)
  	switch {
  	case n == 0:
  		return 0
  	case n == 1:
  		return IndexByte(s, sep[0])
  	case n == len(s):
  		if Equal(sep, s) {
  			return 0
  		}
  		return -1
  	case n > len(s):
  		return -1
  	}
  	c := sep[0]
  	i := 0
  	fails := 0
  	t := s[:len(s)-n+1]
  	for i < len(t) {
  		if t[i] != c {
  			o := IndexByte(t[i:], c)
  			if o < 0 {
  				break
  			}
  			i += o
  		}
  		if Equal(s[i:i+n], sep) {
  			return i
  		}
  		i++
  		fails++
  		if fails >= 4+i>>4 && i < len(t) {
  			// Give up on IndexByte, it isn't skipping ahead
  			// far enough to be better than Rabin-Karp.
  			// Experiments (using IndexPeriodic) suggest
  			// the cutover is about 16 byte skips.
  			// TODO: if large prefixes of sep are matching
  			// we should cutover at even larger average skips,
  			// because Equal becomes that much more expensive.
  			// This code does not take that effect into account.
  			j := indexRabinKarp(s[i:], sep)
  			if j < 0 {
  				return -1
  			}
  			return i + j
  		}
  	}
  	return -1
  }
  
  // Count counts the number of non-overlapping instances of sep in s.
  // If sep is an empty slice, Count returns 1 + the number of UTF-8-encoded code points in s.
  func Count(s, sep []byte) int {
  	return countGeneric(s, sep)
  }
  

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