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// 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 ignore
package strings
//go:noescape
// indexShortStr returns the index of the first instance of c in s, or -1 if c is not present in s.
// indexShortStr requires 2 <= len(c) <= shortStringLen
func indexShortStr(s, c string) int // ../runtime/asm_$GOARCH.s
func supportAVX2() bool // ../runtime/asm_$GOARCH.s
var shortStringLen int
func init() {
if supportAVX2() {
shortStringLen = 63
} else {
shortStringLen = 31
}
}
// 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
}
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