Scott Baker | e7144bc | 2019-10-01 14:16:47 -0700 | [diff] [blame] | 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 | // Package tag contains functionality handling tags and related data. |
| 6 | package tag // import "golang.org/x/text/internal/tag" |
| 7 | |
| 8 | import "sort" |
| 9 | |
| 10 | // An Index converts tags to a compact numeric value. |
| 11 | // |
| 12 | // All elements are of size 4. Tags may be up to 4 bytes long. Excess bytes can |
| 13 | // be used to store additional information about the tag. |
| 14 | type Index string |
| 15 | |
| 16 | // Elem returns the element data at the given index. |
| 17 | func (s Index) Elem(x int) string { |
| 18 | return string(s[x*4 : x*4+4]) |
| 19 | } |
| 20 | |
| 21 | // Index reports the index of the given key or -1 if it could not be found. |
| 22 | // Only the first len(key) bytes from the start of the 4-byte entries will be |
| 23 | // considered for the search and the first match in Index will be returned. |
| 24 | func (s Index) Index(key []byte) int { |
| 25 | n := len(key) |
| 26 | // search the index of the first entry with an equal or higher value than |
| 27 | // key in s. |
| 28 | index := sort.Search(len(s)/4, func(i int) bool { |
| 29 | return cmp(s[i*4:i*4+n], key) != -1 |
| 30 | }) |
| 31 | i := index * 4 |
| 32 | if cmp(s[i:i+len(key)], key) != 0 { |
| 33 | return -1 |
| 34 | } |
| 35 | return index |
| 36 | } |
| 37 | |
| 38 | // Next finds the next occurrence of key after index x, which must have been |
| 39 | // obtained from a call to Index using the same key. It returns x+1 or -1. |
| 40 | func (s Index) Next(key []byte, x int) int { |
| 41 | if x++; x*4 < len(s) && cmp(s[x*4:x*4+len(key)], key) == 0 { |
| 42 | return x |
| 43 | } |
| 44 | return -1 |
| 45 | } |
| 46 | |
| 47 | // cmp returns an integer comparing a and b lexicographically. |
| 48 | func cmp(a Index, b []byte) int { |
| 49 | n := len(a) |
| 50 | if len(b) < n { |
| 51 | n = len(b) |
| 52 | } |
| 53 | for i, c := range b[:n] { |
| 54 | switch { |
| 55 | case a[i] > c: |
| 56 | return 1 |
| 57 | case a[i] < c: |
| 58 | return -1 |
| 59 | } |
| 60 | } |
| 61 | switch { |
| 62 | case len(a) < len(b): |
| 63 | return -1 |
| 64 | case len(a) > len(b): |
| 65 | return 1 |
| 66 | } |
| 67 | return 0 |
| 68 | } |
| 69 | |
| 70 | // Compare returns an integer comparing a and b lexicographically. |
| 71 | func Compare(a string, b []byte) int { |
| 72 | return cmp(Index(a), b) |
| 73 | } |
| 74 | |
| 75 | // FixCase reformats b to the same pattern of cases as form. |
| 76 | // If returns false if string b is malformed. |
| 77 | func FixCase(form string, b []byte) bool { |
| 78 | if len(form) != len(b) { |
| 79 | return false |
| 80 | } |
| 81 | for i, c := range b { |
| 82 | if form[i] <= 'Z' { |
| 83 | if c >= 'a' { |
| 84 | c -= 'z' - 'Z' |
| 85 | } |
| 86 | if c < 'A' || 'Z' < c { |
| 87 | return false |
| 88 | } |
| 89 | } else { |
| 90 | if c <= 'Z' { |
| 91 | c += 'z' - 'Z' |
| 92 | } |
| 93 | if c < 'a' || 'z' < c { |
| 94 | return false |
| 95 | } |
| 96 | } |
| 97 | b[i] = c |
| 98 | } |
| 99 | return true |
| 100 | } |