1 // © 2016 and later: Unicode, Inc. and others.
2 // License & terms of use: http://www.unicode.org/copyright.html
3 /*
4 *******************************************************************************
5 * Copyright (C) 2012-2014, International Business Machines
6 * Corporation and others.  All Rights Reserved.
7 *******************************************************************************
8 * collationfcd.h
9 *
10 * created on: 2012aug18
11 * created by: Markus W. Scherer
12 */
13 
14 #ifndef __COLLATIONFCD_H__
15 #define __COLLATIONFCD_H__
16 
17 #include "unicode/utypes.h"
18 
19 #if !UCONFIG_NO_COLLATION
20 
21 #include "unicode/utf16.h"
22 
23 U_NAMESPACE_BEGIN
24 
25 /**
26  * Data and functions for the FCD check fast path.
27  *
28  * The fast path looks at a pair of 16-bit code units and checks
29  * whether there is an FCD boundary between them;
30  * there is if the first unit has a trailing ccc=0 (!hasTccc(first))
31  * or the second unit has a leading ccc=0 (!hasLccc(second)),
32  * or both.
33  * When the fast path finds a possible non-boundary,
34  * then the FCD check slow path looks at the actual sequence of FCD values.
35  *
36  * This is a pure optimization.
37  * The fast path must at least find all possible non-boundaries.
38  * If the fast path is too pessimistic, it costs performance.
39  *
40  * For a pair of BMP characters, the fast path tests are precise (1 bit per character).
41  *
42  * For a supplementary code point, the two units are its lead and trail surrogates.
43  * We set hasTccc(lead)=true if any of its 1024 associated supplementary code points
44  * has lccc!=0 or tccc!=0.
45  * We set hasLccc(trail)=true for all trail surrogates.
46  * As a result, we leave the fast path if the lead surrogate might start a
47  * supplementary code point that is not FCD-inert.
48  * (So the fast path need not detect that there is a surrogate pair,
49  * nor look ahead to the next full code point.)
50  *
51  * hasLccc(lead)=true if any of its 1024 associated supplementary code points
52  * has lccc!=0, for fast boundary checking between BMP & supplementary.
53  *
54  * hasTccc(trail)=false:
55  * It should only be tested for unpaired trail surrogates which are FCD-inert.
56  */
57 class U_I18N_API CollationFCD {
58 public:
59     static inline UBool hasLccc(UChar32 c) {
60         // assert c <= 0xffff
61         // c can be negative, e.g., U_SENTINEL from UCharIterator;
62         // that is handled in the first test.
63         int32_t i;
64         return
65             // U+0300 is the first character with lccc!=0.
66             c >= 0x300 &&
67             (i = lcccIndex[c >> 5]) != 0 &&
68             (lcccBits[i] & ((uint32_t)1 << (c & 0x1f))) != 0;
69     }
70 
71     static inline UBool hasTccc(UChar32 c) {
72         // assert c <= 0xffff
73         // c can be negative, e.g., U_SENTINEL from UCharIterator;
74         // that is handled in the first test.
75         int32_t i;
76         return
77             // U+00C0 is the first character with tccc!=0.
78             c >= 0xc0 &&
79             (i = tcccIndex[c >> 5]) != 0 &&
80             (tcccBits[i] & ((uint32_t)1 << (c & 0x1f))) != 0;
81     }
82 
83     static inline UBool mayHaveLccc(UChar32 c) {
84         // Handles all of Unicode 0..10FFFF.
85         // c can be negative, e.g., U_SENTINEL.
86         // U+0300 is the first character with lccc!=0.
87         if(c < 0x300) { return FALSE; }
88         if(c > 0xffff) { c = U16_LEAD(c); }
89         int32_t i;
90         return
91             (i = lcccIndex[c >> 5]) != 0 &&
92             (lcccBits[i] & ((uint32_t)1 << (c & 0x1f))) != 0;
93     }
94 
95     /**
96      * Tibetan composite vowel signs (U+0F73, U+0F75, U+0F81)
97      * must be decomposed before reaching the core collation code,
98      * or else some sequences including them, even ones passing the FCD check,
99      * do not yield canonically equivalent results.
100      *
101      * This is a fast and imprecise test.
102      *
103      * @param c a code point
104      * @return TRUE if c is U+0F73, U+0F75 or U+0F81 or one of several other Tibetan characters
105      */
106     static inline UBool maybeTibetanCompositeVowel(UChar32 c) {
107         return (c & 0x1fff01) == 0xf01;
108     }
109 
110     /**
111      * Tibetan composite vowel signs (U+0F73, U+0F75, U+0F81)
112      * must be decomposed before reaching the core collation code,
113      * or else some sequences including them, even ones passing the FCD check,
114      * do not yield canonically equivalent results.
115      *
116      * They have distinct lccc/tccc combinations: 129/130 or 129/132.
117      *
118      * @param fcd16 the FCD value (lccc/tccc combination) of a code point
119      * @return TRUE if fcd16 is from U+0F73, U+0F75 or U+0F81
120      */
121     static inline UBool isFCD16OfTibetanCompositeVowel(uint16_t fcd16) {
122         return fcd16 == 0x8182 || fcd16 == 0x8184;
123     }
124 
125 private:
126     CollationFCD();  // No instantiation.
127 
128     static const uint8_t lcccIndex[2048];
129     static const uint8_t tcccIndex[2048];
130     static const uint32_t lcccBits[];
131     static const uint32_t tcccBits[];
132 };
133 
134 U_NAMESPACE_END
135 
136 #endif  // !UCONFIG_NO_COLLATION
137 #endif  // __COLLATIONFCD_H__
138