| // Copyright 2016 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. |
| |
| package strings |
| |
| //go:noescape |
| |
| // indexShortStr returns the index of the first instance of sep in s, |
| // or -1 if sep is not present in s. |
| // indexShortStr requires 2 <= len(sep) <= shortStringLen |
| func indexShortStr(s, sep string) int // ../runtime/asm_$GOARCH.s |
| |
| // supportsVX reports whether the vector facility is available. |
| // indexShortStr must not be called if the vector facility is not |
| // available. |
| func supportsVX() bool // ../runtime/asm_s390x.s |
| |
| var shortStringLen = -1 |
| |
| func init() { |
| if supportsVX() { |
| shortStringLen = 64 |
| } |
| } |
| |
| // 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 string) int { |
| n := len(sep) |
| switch { |
| case n == 0: |
| return 0 |
| case n == 1: |
| return IndexByte(s, sep[0]) |
| case n == len(s): |
| if sep == s { |
| return 0 |
| } |
| return -1 |
| case n > len(s): |
| return -1 |
| case n <= shortStringLen: |
| // Use brute force when s and sep both are small |
| if len(s) <= 64 { |
| return indexShortStr(s, sep) |
| } |
| c := sep[0] |
| i := 0 |
| t := s[:len(s)-n+1] |
| fails := 0 |
| for i < len(t) { |
| if t[i] != c { |
| // IndexByte skips 16/32 bytes per iteration, |
| // so it's faster than indexShortStr. |
| o := IndexByte(t[i:], c) |
| if o < 0 { |
| return -1 |
| } |
| i += o |
| } |
| if s[i:i+n] == sep { |
| return i |
| } |
| fails++ |
| i++ |
| // Switch to indexShortStr when IndexByte produces too many false positives. |
| // Too many means more that 1 error per 8 characters. |
| // Allow some errors in the beginning. |
| if fails > (i+16)/8 { |
| r := indexShortStr(s[i:], sep) |
| if r >= 0 { |
| return r + i |
| } |
| return -1 |
| } |
| } |
| return -1 |
| } |
| // Rabin-Karp search |
| hashsep, pow := hashStr(sep) |
| var h uint32 |
| for i := 0; i < n; i++ { |
| h = h*primeRK + uint32(s[i]) |
| } |
| if h == hashsep && s[:n] == sep { |
| return 0 |
| } |
| for i := n; i < len(s); { |
| h *= primeRK |
| h += uint32(s[i]) |
| h -= pow * uint32(s[i-n]) |
| i++ |
| if h == hashsep && s[i-n:i] == sep { |
| return i - n |
| } |
| } |
| return -1 |
| } |