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 6 7 package strings 8 9 // TODO: implements short string optimization on non amd64 platforms 10 // and get rid of strings_amd64.go 11 12 // Index returns the index of the first instance of sep in s, or -1 if sep is not present in s. 13 func Index(s, sep string) int { 14 n := len(sep) 15 switch { 16 case n == 0: 17 return 0 18 case n == 1: 19 return IndexByte(s, sep[0]) 20 case n == len(s): 21 if sep == s { 22 return 0 23 } 24 return -1 25 case n > len(s): 26 return -1 27 } 28 // Rabin-Karp search 29 hashsep, pow := hashStr(sep) 30 var h uint32 31 for i := 0; i < n; i++ { 32 h = h*primeRK + uint32(s[i]) 33 } 34 if h == hashsep && s[:n] == sep { 35 return 0 36 } 37 for i := n; i < len(s); { 38 h *= primeRK 39 h += uint32(s[i]) 40 h -= pow * uint32(s[i-n]) 41 i++ 42 if h == hashsep && s[i-n:i] == sep { 43 return i - n 44 } 45 } 46 return -1 47 } 48
