1/*
2******************************************************************************
3*
4*   Copyright (C) 1999-2006, International Business Machines
5*   Corporation and others.  All Rights Reserved.
6*
7******************************************************************************
8*   file name:  utf_impl.c
9*   encoding:   US-ASCII
10*   tab size:   8 (not used)
11*   indentation:4
12*
13*   created on: 1999sep13
14*   created by: Markus W. Scherer
15*
16*   This file provides implementation functions for macros in the utfXX.h
17*   that would otherwise be too long as macros.
18*/
19
20#include "base/third_party/icu/icu_utf.h"
21
22namespace base_icu {
23
24/**
25 * UTF8_ERROR_VALUE_1 and UTF8_ERROR_VALUE_2 are special error values for UTF-8,
26 * which need 1 or 2 bytes in UTF-8:
27 * \code
28 * U+0015 = NAK = Negative Acknowledge, C0 control character
29 * U+009f = highest C1 control character
30 * \endcode
31 *
32 * These are used by UTF8_..._SAFE macros so that they can return an error value
33 * that needs the same number of code units (bytes) as were seen by
34 * a macro. They should be tested with UTF_IS_ERROR() or UTF_IS_VALID().
35 *
36 * @deprecated ICU 2.4. Obsolete, see utf_old.h.
37 */
38#define CBUTF8_ERROR_VALUE_1 0x15
39
40/**
41 * See documentation on UTF8_ERROR_VALUE_1 for details.
42 *
43 * @deprecated ICU 2.4. Obsolete, see utf_old.h.
44 */
45#define CBUTF8_ERROR_VALUE_2 0x9f
46
47
48/**
49 * Error value for all UTFs. This code point value will be set by macros with e>
50 * checking if an error is detected.
51 *
52 * @deprecated ICU 2.4. Obsolete, see utf_old.h.
53 */
54#define CBUTF_ERROR_VALUE 0xffff
55
56/*
57 * This table could be replaced on many machines by
58 * a few lines of assembler code using an
59 * "index of first 0-bit from msb" instruction and
60 * one or two more integer instructions.
61 *
62 * For example, on an i386, do something like
63 * - MOV AL, leadByte
64 * - NOT AL         (8-bit, leave b15..b8==0..0, reverse only b7..b0)
65 * - MOV AH, 0
66 * - BSR BX, AX     (16-bit)
67 * - MOV AX, 6      (result)
68 * - JZ finish      (ZF==1 if leadByte==0xff)
69 * - SUB AX, BX (result)
70 * -finish:
71 * (BSR: Bit Scan Reverse, scans for a 1-bit, starting from the MSB)
72 *
73 * In Unicode, all UTF-8 byte sequences with more than 4 bytes are illegal;
74 * lead bytes above 0xf4 are illegal.
75 * We keep them in this table for skipping long ISO 10646-UTF-8 sequences.
76 */
77const uint8
78utf8_countTrailBytes[256]={
79    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
80    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
81    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
82    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
83
84    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
85    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
86    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
87    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
88
89    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
90    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
91    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
92    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
93
94    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
95    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
96
97    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
98    3, 3, 3, 3, 3,
99    3, 3, 3,    /* illegal in Unicode */
100    4, 4, 4, 4, /* illegal in Unicode */
101    5, 5,       /* illegal in Unicode */
102    0, 0        /* illegal bytes 0xfe and 0xff */
103};
104
105static const UChar32
106utf8_minLegal[4]={ 0, 0x80, 0x800, 0x10000 };
107
108static const UChar32
109utf8_errorValue[6]={
110    CBUTF8_ERROR_VALUE_1, CBUTF8_ERROR_VALUE_2, CBUTF_ERROR_VALUE, 0x10ffff,
111    0x3ffffff, 0x7fffffff
112};
113
114/*
115 * Handle the non-inline part of the U8_NEXT() macro and its obsolete sibling
116 * UTF8_NEXT_CHAR_SAFE().
117 *
118 * The "strict" parameter controls the error behavior:
119 * <0  "Safe" behavior of U8_NEXT(): All illegal byte sequences yield a negative
120 *     code point result.
121 *  0  Obsolete "safe" behavior of UTF8_NEXT_CHAR_SAFE(..., FALSE):
122 *     All illegal byte sequences yield a positive code point such that this
123 *     result code point would be encoded with the same number of bytes as
124 *     the illegal sequence.
125 * >0  Obsolete "strict" behavior of UTF8_NEXT_CHAR_SAFE(..., TRUE):
126 *     Same as the obsolete "safe" behavior, but non-characters are also treated
127 *     like illegal sequences.
128 *
129 * The special negative (<0) value -2 is used for lenient treatment of surrogate
130 * code points as legal. Some implementations use this for roundtripping of
131 * Unicode 16-bit strings that are not well-formed UTF-16, that is, they
132 * contain unpaired surrogates.
133 *
134 * Note that a UBool is the same as an int8_t.
135 */
136UChar32
137utf8_nextCharSafeBody(const uint8 *s, int32 *pi, int32 length, UChar32 c, UBool strict) {
138    int32 i=*pi;
139    uint8 count=CBU8_COUNT_TRAIL_BYTES(c);
140    if((i)+count<=(length)) {
141        uint8 trail, illegal=0;
142
143        CBU8_MASK_LEAD_BYTE((c), count);
144        /* count==0 for illegally leading trail bytes and the illegal bytes 0xfe and 0xff */
145        switch(count) {
146        /* each branch falls through to the next one */
147        case 5:
148        case 4:
149            /* count>=4 is always illegal: no more than 3 trail bytes in Unicode's UTF-8 */
150            illegal=1;
151            break;
152        case 3:
153            trail=s[(i)++];
154            (c)=((c)<<6)|(trail&0x3f);
155            if(c<0x110) {
156                illegal|=(trail&0xc0)^0x80;
157            } else {
158                /* code point>0x10ffff, outside Unicode */
159                illegal=1;
160                break;
161            }
162        case 2:
163            trail=s[(i)++];
164            (c)=((c)<<6)|(trail&0x3f);
165            illegal|=(trail&0xc0)^0x80;
166        case 1:
167            trail=s[(i)++];
168            (c)=((c)<<6)|(trail&0x3f);
169            illegal|=(trail&0xc0)^0x80;
170            break;
171        case 0:
172            if(strict>=0) {
173                return CBUTF8_ERROR_VALUE_1;
174            } else {
175                return CBU_SENTINEL;
176            }
177        /* no default branch to optimize switch()  - all values are covered */
178        }
179
180        /*
181         * All the error handling should return a value
182         * that needs count bytes so that UTF8_GET_CHAR_SAFE() works right.
183         *
184         * Starting with Unicode 3.0.1, non-shortest forms are illegal.
185         * Starting with Unicode 3.2, surrogate code points must not be
186         * encoded in UTF-8, and there are no irregular sequences any more.
187         *
188         * U8_ macros (new in ICU 2.4) return negative values for error conditions.
189         */
190
191        /* correct sequence - all trail bytes have (b7..b6)==(10)? */
192        /* illegal is also set if count>=4 */
193        if(illegal || (c)<utf8_minLegal[count] || (CBU_IS_SURROGATE(c) && strict!=-2)) {
194            /* error handling */
195            uint8 errorCount=count;
196            /* don't go beyond this sequence */
197            i=*pi;
198            while(count>0 && CBU8_IS_TRAIL(s[i])) {
199                ++(i);
200                --count;
201            }
202            if(strict>=0) {
203                c=utf8_errorValue[errorCount-count];
204            } else {
205                c=CBU_SENTINEL;
206            }
207        } else if((strict)>0 && CBU_IS_UNICODE_NONCHAR(c)) {
208            /* strict: forbid non-characters like U+fffe */
209            c=utf8_errorValue[count];
210        }
211    } else /* too few bytes left */ {
212        /* error handling */
213        int32 i0=i;
214        /* don't just set (i)=(length) in case there is an illegal sequence */
215        while((i)<(length) && CBU8_IS_TRAIL(s[i])) {
216            ++(i);
217        }
218        if(strict>=0) {
219            c=utf8_errorValue[i-i0];
220        } else {
221            c=CBU_SENTINEL;
222        }
223    }
224    *pi=i;
225    return c;
226}
227
228}  // namespace base_icu
229