1 // Copyright 2016 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 package strings 6 7 //go:noescape 8 9 // indexShortStr returns the index of the first instance of sep in s, 10 // or -1 if sep is not present in s. 11 // indexShortStr requires 2 <= len(sep) <= shortStringLen 12 func indexShortStr(s, sep string) int // ../runtime/asm_$GOARCH.s 13 14 // supportsVX reports whether the vector facility is available. 15 // indexShortStr must not be called if the vector facility is not 16 // available. 17 func supportsVX() bool // ../runtime/asm_s390x.s 18 19 var shortStringLen = -1 20 21 func init() { 22 if supportsVX() { 23 shortStringLen = 64 24 } 25 } 26 27 // Index returns the index of the first instance of substr in s, or -1 if substr is not present in s. 28 func Index(s, substr string) int { 29 n := len(substr) 30 switch { 31 case n == 0: 32 return 0 33 case n == 1: 34 return IndexByte(s, substr[0]) 35 case n == len(s): 36 if substr == s { 37 return 0 38 } 39 return -1 40 case n > len(s): 41 return -1 42 case n <= shortStringLen: 43 // Use brute force when s and substr both are small 44 if len(s) <= 64 { 45 return indexShortStr(s, substr) 46 } 47 c := substr[0] 48 i := 0 49 t := s[:len(s)-n+1] 50 fails := 0 51 for i < len(t) { 52 if t[i] != c { 53 // IndexByte skips 16/32 bytes per iteration, 54 // so it's faster than indexShortStr. 55 o := IndexByte(t[i:], c) 56 if o < 0 { 57 return -1 58 } 59 i += o 60 } 61 if s[i:i+n] == substr { 62 return i 63 } 64 fails++ 65 i++ 66 // Switch to indexShortStr when IndexByte produces too many false positives. 67 // Too many means more that 1 error per 8 characters. 68 // Allow some errors in the beginning. 69 if fails > (i+16)/8 { 70 r := indexShortStr(s[i:], substr) 71 if r >= 0 { 72 return r + i 73 } 74 return -1 75 } 76 } 77 return -1 78 } 79 return indexRabinKarp(s, substr) 80 } 81 82 // Count counts the number of non-overlapping instances of substr in s. 83 // If substr is an empty string, Count returns 1 + the number of Unicode code points in s. 84 func Count(s, substr string) int { 85 return countGeneric(s, substr) 86 } 87
