50 lines
1.1 KiB
Go
50 lines
1.1 KiB
Go
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// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package strings
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// indexShortStr returns the index of the first instance of c in s, or -1 if c is not present in s.
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// indexShortStr requires 2 <= len(c) <= shortStringLen
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func indexShortStr(s, c string) int // ../runtime/asm_$GOARCH.s
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const shortStringLen = 31
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// Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
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func Index(s, sep string) int {
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n := len(sep)
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switch {
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case n == 0:
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return 0
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case n == 1:
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return IndexByte(s, sep[0])
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case n <= shortStringLen:
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return indexShortStr(s, sep)
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case n == len(s):
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if sep == s {
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return 0
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}
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return -1
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case n > len(s):
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return -1
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}
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// Rabin-Karp search
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hashsep, pow := hashStr(sep)
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var h uint32
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for i := 0; i < n; i++ {
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h = h*primeRK + uint32(s[i])
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}
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if h == hashsep && s[:n] == sep {
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return 0
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}
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for i := n; i < len(s); {
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h *= primeRK
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h += uint32(s[i])
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h -= pow * uint32(s[i-n])
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i++
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if h == hashsep && s[i-n:i] == sep {
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return i - n
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}
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}
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return -1
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}
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