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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.
// Package tag contains functionality handling tags and related data.
package tag
import "sort"
// An Index converts tags to a compact numeric value.
//
// All elements are of size 4. Tags may be up to 4 bytes long. Excess bytes can
// be used to store additional information about the tag.
type Index string
// Elem returns the element data at the given index.
func (s Index) Elem(x int) string {
return string(s[x*4 : x*4+4])
}
// Index reports the index of the given key or -1 if it could not be found.
// Only the first len(key) bytes from the start of the 4-byte entries will be
// considered for the search and the first match in Index will be returned.
func (s Index) Index(key []byte) int {
n := len(key)
// search the index of the first entry with an equal or higher value than
// key in s.
index := sort.Search(len(s)/4, func(i int) bool {
return cmp(s[i*4:i*4+n], key) != -1
})
i := index * 4
if cmp(s[i:i+len(key)], key) != 0 {
return -1
}
return index
}
// Next finds the next occurrence of key after index x, which must have been
// obtained from a call to Index using the same key. It returns x+1 or -1.
func (s Index) Next(key []byte, x int) int {
if x++; x*4 < len(s) && cmp(s[x*4:x*4+len(key)], key) == 0 {
return x
}
return -1
}
// cmp returns an integer comparing a and b lexicographically.
func cmp(a Index, b []byte) int {
n := len(a)
if len(b) < n {
n = len(b)
}
for i, c := range b[:n] {
switch {
case a[i] > c:
return 1
case a[i] < c:
return -1
}
}
switch {
case len(a) < len(b):
return -1
case len(a) > len(b):
return 1
}
return 0
}
// Compare returns an integer comparing a and b lexicographically.
func Compare(a string, b []byte) int {
return cmp(Index(a), b)
}
// FixCase reformats b to the same pattern of cases as form.
// If returns false if string b is malformed.
func FixCase(form string, b []byte) bool {
if len(form) != len(b) {
return false
}
for i, c := range b {
if form[i] <= 'Z' {
if c >= 'a' {
c -= 'z' - 'Z'
}
if c < 'A' || 'Z' < c {
return false
}
} else {
if c <= 'Z' {
c += 'z' - 'Z'
}
if c < 'a' || 'z' < c {
return false
}
}
b[i] = c
}
return true
}
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