1 // Copyright 2008 The RE2 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 // Unicode case folding tables.
6 
7 // The Unicode case folding tables encode the mapping from one Unicode point
8 // to the next largest Unicode point with equivalent folding.  The largest
9 // point wraps back to the first.  For example, the tables map:
10 //
11 //     'A' -> 'a'
12 //     'a' -> 'A'
13 //
14 //     'K' -> 'k'
15 //     'k' -> 'K'  (Kelvin symbol)
16 //     'K' -> 'K'
17 //
18 // Like everything Unicode, these tables are big.  If we represent the table
19 // as a sorted list of uint32 pairs, it has 2049 entries and is 16 kB.
20 // Most table entries look like the ones around them:
21 // 'A' maps to 'A'+32, 'B' maps to 'B'+32, etc.
22 // Instead of listing all the pairs explicitly, we make a list of ranges
23 // and deltas, so that the table entries for 'A' through 'Z' can be represented
24 // as a single entry { 'A', 'Z', +32 }.
25 //
26 // In addition to blocks that map to each other (A-Z mapping to a-z)
27 // there are blocks of pairs that individually map to each other
28 // (for example, 0100<->0101, 0102<->0103, 0104<->0105, ...).
29 // For those, the special delta value EvenOdd marks even/odd pairs
30 // (if even, add 1; if odd, subtract 1), and OddEven marks odd/even pairs.
31 //
32 // In this form, the table has 274 entries, about 3kB.  If we were to split
33 // the table into one for 16-bit codes and an overflow table for larger ones,
34 // we could get it down to about 1.5kB, but that's not worth the complexity.
35 //
36 // The grouped form also allows for efficient fold range calculations
37 // rather than looping one character at a time.
38 
39 #ifndef RE2_UNICODE_CASEFOLD_H__
40 #define RE2_UNICODE_CASEFOLD_H__
41 
42 #include "util/util.h"
43 
44 namespace re2 {
45 
46 enum {
47   EvenOdd = 1,
48   OddEven = -1,
49   EvenOddSkip = 1<<30,
50   OddEvenSkip,
51 };
52 
53 struct CaseFold {
54   uint32 lo;
55   uint32 hi;
56   int32 delta;
57 };
58 
59 extern const CaseFold unicode_casefold[];
60 extern const int num_unicode_casefold;
61 
62 extern const CaseFold unicode_tolower[];
63 extern const int num_unicode_tolower;
64 
65 // Returns the CaseFold* in the tables that contains rune.
66 // If rune is not in the tables, returns the first CaseFold* after rune.
67 // If rune is larger than any value in the tables, returns NULL.
68 extern const CaseFold* LookupCaseFold(const CaseFold*, int, Rune rune);
69 
70 // Returns the result of applying the fold f to the rune r.
71 extern Rune ApplyFold(const CaseFold *f, Rune r);
72 
73 }  // namespace re2
74 
75 #endif  // RE2_UNICODE_CASEFOLD_H__
76