src/bytes/bytes_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 bytes

// TODO: implements short string optimization on non amd64 platforms
// and get rid of bytes_amd64.go

// 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)
	if n == 0 {
		return 0
	}
	if n > len(s) {
		return -1
	}
	c := sep[0]
	if n == 1 {
		return IndexByte(s, c)
	}
	i := 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++
	}
	return -1
}