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Source file src/strings/strings_generic.go

Documentation: strings

  // 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
  
  package strings
  
  // TODO: implements short string optimization on non amd64 platforms
  // and get rid of strings_amd64.go
  
  // Index returns the index of the first instance of substr in s, or -1 if substr is not present in s.
  func Index(s, substr string) int {
  	n := len(substr)
  	switch {
  	case n == 0:
  		return 0
  	case n == 1:
  		return IndexByte(s, substr[0])
  	case n == len(s):
  		if substr == s {
  			return 0
  		}
  		return -1
  	case n > len(s):
  		return -1
  	}
  	// Rabin-Karp search
  	hashss, pow := hashStr(substr)
  	var h uint32
  	for i := 0; i < n; i++ {
  		h = h*primeRK + uint32(s[i])
  	}
  	if h == hashss && s[:n] == substr {
  		return 0
  	}
  	for i := n; i < len(s); {
  		h *= primeRK
  		h += uint32(s[i])
  		h -= pow * uint32(s[i-n])
  		i++
  		if h == hashss && s[i-n:i] == substr {
  			return i - n
  		}
  	}
  	return -1
  }
  
  // Count counts the number of non-overlapping instances of substr in s.
  // If substr is an empty string, Count returns 1 + the number of Unicode code points in s.
  func Count(s, substr string) int {
  	return countGeneric(s, substr)
  }
  

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