github.com/aloncn/graphics-go@v0.0.1/src/strings/strings_generic.go (about)

     1  // Copyright 2015 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  // +build !amd64
     6  
     7  package strings
     8  
     9  // TODO: implements short string optimization on non amd64 platforms
    10  // and get rid of strings_amd64.go
    11  
    12  // Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
    13  func Index(s, sep string) int {
    14  	n := len(sep)
    15  	switch {
    16  	case n == 0:
    17  		return 0
    18  	case n == 1:
    19  		return IndexByte(s, sep[0])
    20  	case n == len(s):
    21  		if sep == s {
    22  			return 0
    23  		}
    24  		return -1
    25  	case n > len(s):
    26  		return -1
    27  	}
    28  	// Rabin-Karp search
    29  	hashsep, pow := hashStr(sep)
    30  	var h uint32
    31  	for i := 0; i < n; i++ {
    32  		h = h*primeRK + uint32(s[i])
    33  	}
    34  	if h == hashsep && s[:n] == sep {
    35  		return 0
    36  	}
    37  	for i := n; i < len(s); {
    38  		h *= primeRK
    39  		h += uint32(s[i])
    40  		h -= pow * uint32(s[i-n])
    41  		i++
    42  		if h == hashsep && s[i-n:i] == sep {
    43  			return i - n
    44  		}
    45  	}
    46  	return -1
    47  }