Mercurial > hg > CbC > CbC_gcc
view libgo/go/strings/strings_amd64.go @ 136:4627f235cf2a
fix c-next example
author | Shinji KONO <kono@ie.u-ryukyu.ac.jp> |
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date | Thu, 08 Nov 2018 14:11:56 +0900 |
parents | 04ced10e8804 |
children |
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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 } // Rabin-Karp search hashss, pow := hashStr(substr) var h uint32 for i := 0; i < n; i++ { h = h*primeRK + uint32(s[i]) } if h == hashss && s[:n] == substr { return 0 } for i := n; i < len(s); { h *= primeRK h += uint32(s[i]) h -= pow * uint32(s[i-n]) i++ if h == hashss && s[i-n:i] == substr { return i - n } } return -1 } // 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) }