github.com/kdevb0x/go@v0.0.0-20180115030120-39687051e9e7/src/bytes/bytes_s390x.go (about)

     1  // Copyright 2016 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  package bytes
     6  
     7  //go:noescape
     8  
     9  // indexShortStr returns the index of the first instance of sep in s,
    10  // or -1 if sep is not present in s.
    11  // indexShortStr requires 2 <= len(sep) <= shortStringLen
    12  func indexShortStr(s, c []byte) int // ../runtime/asm_s390x.s
    13  
    14  // supportsVX reports whether the vector facility is available.
    15  // indexShortStr must not be called if the vector facility is not
    16  // available.
    17  func supportsVX() bool // ../runtime/asm_s390x.s
    18  
    19  var shortStringLen = -1
    20  
    21  func init() {
    22  	if supportsVX() {
    23  		shortStringLen = 64
    24  	}
    25  }
    26  
    27  // Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
    28  func Index(s, sep []byte) int {
    29  	n := len(sep)
    30  	switch {
    31  	case n == 0:
    32  		return 0
    33  	case n == 1:
    34  		return IndexByte(s, sep[0])
    35  	case n == len(s):
    36  		if Equal(sep, s) {
    37  			return 0
    38  		}
    39  		return -1
    40  	case n > len(s):
    41  		return -1
    42  	case n <= shortStringLen:
    43  		// Use brute force when s and sep both are small
    44  		if len(s) <= 64 {
    45  			return indexShortStr(s, sep)
    46  		}
    47  		c := sep[0]
    48  		i := 0
    49  		t := s[:len(s)-n+1]
    50  		fails := 0
    51  		for i < len(t) {
    52  			if t[i] != c {
    53  				// IndexByte skips 16/32 bytes per iteration,
    54  				// so it's faster than indexShortStr.
    55  				o := IndexByte(t[i:], c)
    56  				if o < 0 {
    57  					return -1
    58  				}
    59  				i += o
    60  			}
    61  			if Equal(s[i:i+n], sep) {
    62  				return i
    63  			}
    64  			fails++
    65  			i++
    66  			// Switch to indexShortStr when IndexByte produces too many false positives.
    67  			// Too many means more that 1 error per 8 characters.
    68  			// Allow some errors in the beginning.
    69  			if fails > (i+16)/8 {
    70  				r := indexShortStr(s[i:], sep)
    71  				if r >= 0 {
    72  					return r + i
    73  				}
    74  				return -1
    75  			}
    76  		}
    77  		return -1
    78  	}
    79  	return indexRabinKarp(s, sep)
    80  }
    81  
    82  // Count counts the number of non-overlapping instances of sep in s.
    83  // If sep is an empty slice, Count returns 1 + the number of UTF-8-encoded code points in s.
    84  func Count(s, sep []byte) int {
    85  	return countGeneric(s, sep)
    86  }