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 bytes 6 7 import "internal/cpu" 8 9 //go:noescape 10 11 // indexShortStr returns the index of the first instance of c in s, or -1 if c is not present in s. 12 // indexShortStr requires 2 <= len(c) <= shortStringLen 13 func indexShortStr(s, c []byte) int // ../runtime/asm_amd64.s 14 func countByte(s []byte, c byte) int // ../runtime/asm_amd64.s 15 16 var shortStringLen int 17 18 func init() { 19 if cpu.X86.HasAVX2 { 20 shortStringLen = 63 21 } else { 22 shortStringLen = 31 23 } 24 } 25 26 // Index returns the index of the first instance of sep in s, or -1 if sep is not present in s. 27 func Index(s, sep []byte) int { 28 n := len(sep) 29 switch { 30 case n == 0: 31 return 0 32 case n == 1: 33 return IndexByte(s, sep[0]) 34 case n == len(s): 35 if Equal(sep, s) { 36 return 0 37 } 38 return -1 39 case n > len(s): 40 return -1 41 case n <= shortStringLen: 42 // Use brute force when s and sep both are small 43 if len(s) <= 64 { 44 return indexShortStr(s, sep) 45 } 46 c := sep[0] 47 i := 0 48 t := s[:len(s)-n+1] 49 fails := 0 50 for i < len(t) { 51 if t[i] != c { 52 // IndexByte skips 16/32 bytes per iteration, 53 // so it's faster than indexShortStr. 54 o := IndexByte(t[i:], c) 55 if o < 0 { 56 return -1 57 } 58 i += o 59 } 60 if Equal(s[i:i+n], sep) { 61 return i 62 } 63 fails++ 64 i++ 65 // Switch to indexShortStr when IndexByte produces too many false positives. 66 // Too many means more that 1 error per 8 characters. 67 // Allow some errors in the beginning. 68 if fails > (i+16)/8 { 69 r := indexShortStr(s[i:], sep) 70 if r >= 0 { 71 return r + i 72 } 73 return -1 74 } 75 } 76 return -1 77 } 78 return indexRabinKarp(s, sep) 79 } 80 81 // Count counts the number of non-overlapping instances of sep in s. 82 // If sep is an empty slice, Count returns 1 + the number of UTF-8-encoded code points in s. 83 func Count(s, sep []byte) int { 84 if len(sep) == 1 && cpu.X86.HasPOPCNT { 85 return countByte(s, sep[0]) 86 } 87 return countGeneric(s, sep) 88 } 89
