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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
import "internal/cpu"
//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_amd64.s
func countByte(s string, c byte) int // ../runtime/asm_amd64.s
var shortStringLen int
func init() {
if cpu.X86.HasAVX2 {
shortStringLen = 63
} else {
shortStringLen = 31
}
}
// 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
case n <= shortStringLen:
// Use brute force when s and substr both are small
if len(s) <= 64 {
return indexShortStr(s, substr)
}
c := substr[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] == substr {
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:], substr)
if r >= 0 {
return r + i
}
return -1
}
}
return -1
}
return indexRabinKarp(s, substr)
}
// 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 {
if len(substr) == 1 && cpu.X86.HasPOPCNT {
return countByte(s, byte(substr[0]))
}
return countGeneric(s, substr)
}
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