libgo/go/strings/strings_generic.go

   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
   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 }