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76 lines
2.5 KiB
C++
76 lines
2.5 KiB
C++
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// Copyright 2008 The RE2 Authors. All Rights Reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Unicode case folding tables.
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// The Unicode case folding tables encode the mapping from one Unicode point
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// to the next largest Unicode point with equivalent folding. The largest
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// point wraps back to the first. For example, the tables map:
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//
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// 'A' -> 'a'
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// 'a' -> 'A'
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//
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// 'K' -> 'k'
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// 'k' -> 'K' (Kelvin symbol)
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// 'K' -> 'K'
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//
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// Like everything Unicode, these tables are big. If we represent the table
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// as a sorted list of uint32 pairs, it has 2049 entries and is 16 kB.
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// Most table entries look like the ones around them:
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// 'A' maps to 'A'+32, 'B' maps to 'B'+32, etc.
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// Instead of listing all the pairs explicitly, we make a list of ranges
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// and deltas, so that the table entries for 'A' through 'Z' can be represented
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// as a single entry { 'A', 'Z', +32 }.
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//
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// In addition to blocks that map to each other (A-Z mapping to a-z)
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// there are blocks of pairs that individually map to each other
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// (for example, 0100<->0101, 0102<->0103, 0104<->0105, ...).
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// For those, the special delta value EvenOdd marks even/odd pairs
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// (if even, add 1; if odd, subtract 1), and OddEven marks odd/even pairs.
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//
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// In this form, the table has 274 entries, about 3kB. If we were to split
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// the table into one for 16-bit codes and an overflow table for larger ones,
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// we could get it down to about 1.5kB, but that's not worth the complexity.
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//
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// The grouped form also allows for efficient fold range calculations
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// rather than looping one character at a time.
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#ifndef RE2_UNICODE_CASEFOLD_H__
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#define RE2_UNICODE_CASEFOLD_H__
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#include "util/util.h"
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namespace re2 {
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enum {
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EvenOdd = 1,
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OddEven = -1,
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EvenOddSkip = 1<<30,
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OddEvenSkip,
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};
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struct CaseFold {
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uint32 lo;
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uint32 hi;
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int32 delta;
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};
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extern const CaseFold unicode_casefold[];
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extern const int num_unicode_casefold;
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extern const CaseFold unicode_tolower[];
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extern const int num_unicode_tolower;
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// Returns the CaseFold* in the tables that contains rune.
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// If rune is not in the tables, returns the first CaseFold* after rune.
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// If rune is larger than any value in the tables, returns NULL.
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extern const CaseFold* LookupCaseFold(const CaseFold*, int, Rune rune);
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// Returns the result of applying the fold f to the rune r.
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extern Rune ApplyFold(const CaseFold *f, Rune r);
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} // namespace re2
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#endif // RE2_UNICODE_CASEFOLD_H__
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