libgo/go/strings/strings_generic.go

// 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
	}
	c := substr[0]
	i := 0
	t := s[:len(s)-n+1]
	fails := 0
	for i < len(t) {
		if t[i] != c {
			o := IndexByte(t[i:], c)
			if o < 0 {
				return -1
			}
			i += o
		}
		if s[i:i+n] == substr {
			return i
		}
		i++
		fails++
		if fails >= 4+i>>4 && i < len(t) {
			// See comment in ../bytes/bytes_generic.go.
			j := indexRabinKarp(s[i:], substr)
			if j < 0 {
				return -1
			}
			return i + j
		}
	}
	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)
}