| // 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) |
| } |