1/*
2******************************************************************************
3*
4*   Copyright (C) 1999-2012, 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/* set import/export definitions */
21#ifndef U_UTF8_IMPL
22#   define U_UTF8_IMPL
23#endif
24
25#include "unicode/utypes.h"
26#include "unicode/utf.h"
27#include "unicode/utf8.h"
28#include "unicode/utf_old.h"
29#include "uassert.h"
30
31/*
32 * This table could be replaced on many machines by
33 * a few lines of assembler code using an
34 * "index of first 0-bit from msb" instruction and
35 * one or two more integer instructions.
36 *
37 * For example, on an i386, do something like
38 * - MOV AL, leadByte
39 * - NOT AL         (8-bit, leave b15..b8==0..0, reverse only b7..b0)
40 * - MOV AH, 0
41 * - BSR BX, AX     (16-bit)
42 * - MOV AX, 6      (result)
43 * - JZ finish      (ZF==1 if leadByte==0xff)
44 * - SUB AX, BX (result)
45 * -finish:
46 * (BSR: Bit Scan Reverse, scans for a 1-bit, starting from the MSB)
47 *
48 * In Unicode, all UTF-8 byte sequences with more than 4 bytes are illegal;
49 * lead bytes above 0xf4 are illegal.
50 * We keep them in this table for skipping long ISO 10646-UTF-8 sequences.
51 */
52U_EXPORT const uint8_t
53utf8_countTrailBytes[256]={
54    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
55    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
56    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
57    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
58
59    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
60    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
61    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
62    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
63
64    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
65    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
66    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
67    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
68
69    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
70    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
71
72    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
73    3, 3, 3, 3, 3,
74    3, 3, 3,    /* illegal in Unicode */
75    4, 4, 4, 4, /* illegal in Unicode */
76    5, 5,       /* illegal in Unicode */
77    0, 0        /* illegal bytes 0xfe and 0xff */
78};
79
80static const UChar32
81utf8_minLegal[4]={ 0, 0x80, 0x800, 0x10000 };
82
83static const UChar32
84utf8_errorValue[6]={
85    UTF8_ERROR_VALUE_1, UTF8_ERROR_VALUE_2, UTF_ERROR_VALUE, 0x10ffff,
86    0x3ffffff, 0x7fffffff
87};
88
89static UChar32
90errorValue(int32_t count, int8_t strict) {
91    if(strict>=0) {
92        return utf8_errorValue[count];
93    } else if(strict==-3) {
94        return 0xfffd;
95    } else {
96        return U_SENTINEL;
97    }
98}
99
100/*
101 * Handle the non-inline part of the U8_NEXT() and U8_NEXT_FFFD() macros
102 * and their obsolete sibling UTF8_NEXT_CHAR_SAFE().
103 *
104 * U8_NEXT() supports NUL-terminated strings indicated via length<0.
105 *
106 * The "strict" parameter controls the error behavior:
107 * <0  "Safe" behavior of U8_NEXT():
108 *     -1: All illegal byte sequences yield U_SENTINEL=-1.
109 *     -2: Same as -1, except for lenient treatment of surrogate code points as legal.
110 *         Some implementations use this for roundtripping of
111 *         Unicode 16-bit strings that are not well-formed UTF-16, that is, they
112 *         contain unpaired surrogates.
113 *     -3: All illegal byte sequences yield U+FFFD.
114 *  0  Obsolete "safe" behavior of UTF8_NEXT_CHAR_SAFE(..., FALSE):
115 *     All illegal byte sequences yield a positive code point such that this
116 *     result code point would be encoded with the same number of bytes as
117 *     the illegal sequence.
118 * >0  Obsolete "strict" behavior of UTF8_NEXT_CHAR_SAFE(..., TRUE):
119 *     Same as the obsolete "safe" behavior, but non-characters are also treated
120 *     like illegal sequences.
121 *
122 * Note that a UBool is the same as an int8_t.
123 */
124U_CAPI UChar32 U_EXPORT2
125utf8_nextCharSafeBody(const uint8_t *s, int32_t *pi, int32_t length, UChar32 c, UBool strict) {
126    int32_t i=*pi;
127    uint8_t count=U8_COUNT_TRAIL_BYTES(c);
128    U_ASSERT(count <= 5); /* U8_COUNT_TRAIL_BYTES returns value 0...5 */
129    if(i+count<=length || length<0) {
130        uint8_t trail;
131
132        U8_MASK_LEAD_BYTE(c, count);
133        /* support NUL-terminated strings: do not read beyond the first non-trail byte */
134        switch(count) {
135        /* each branch falls through to the next one */
136        case 0:
137            /* count==0 for illegally leading trail bytes and the illegal bytes 0xfe and 0xff */
138        case 5:
139        case 4:
140            /* count>=4 is always illegal: no more than 3 trail bytes in Unicode's UTF-8 */
141            break;
142        case 3:
143            trail=s[i++]-0x80;
144            c=(c<<6)|trail;
145            /* c>=0x110 would result in code point>0x10ffff, outside Unicode */
146            if(c>=0x110 || trail>0x3f) { break; }
147        case 2:
148            trail=s[i++]-0x80;
149            c=(c<<6)|trail;
150            /*
151             * test for a surrogate d800..dfff unless we are lenient:
152             * before the last (c<<6), a surrogate is c=360..37f
153             */
154            if(((c&0xffe0)==0x360 && strict!=-2) || trail>0x3f) { break; }
155        case 1:
156            trail=s[i++]-0x80;
157            c=(c<<6)|trail;
158            if(trail>0x3f) { break; }
159            /* correct sequence - all trail bytes have (b7..b6)==(10) */
160            if(c>=utf8_minLegal[count] &&
161                    /* strict: forbid non-characters like U+fffe */
162                    (strict<=0 || !U_IS_UNICODE_NONCHAR(c))) {
163                *pi=i;
164                return c;
165            }
166        /* no default branch to optimize switch()  - all values are covered */
167        }
168    } else {
169        /* too few bytes left */
170        count=length-i;
171    }
172
173    /* error handling */
174    i=*pi;
175    while(count>0 && U8_IS_TRAIL(s[i])) {
176        ++i;
177        --count;
178    }
179    c=errorValue(i-*pi, strict);
180    *pi=i;
181    return c;
182}
183
184U_CAPI int32_t U_EXPORT2
185utf8_appendCharSafeBody(uint8_t *s, int32_t i, int32_t length, UChar32 c, UBool *pIsError) {
186    if((uint32_t)(c)<=0x7ff) {
187        if((i)+1<(length)) {
188            (s)[(i)++]=(uint8_t)(((c)>>6)|0xc0);
189            (s)[(i)++]=(uint8_t)(((c)&0x3f)|0x80);
190            return i;
191        }
192    } else if((uint32_t)(c)<=0xffff) {
193        /* Starting with Unicode 3.2, surrogate code points must not be encoded in UTF-8. */
194        if((i)+2<(length) && !U_IS_SURROGATE(c)) {
195            (s)[(i)++]=(uint8_t)(((c)>>12)|0xe0);
196            (s)[(i)++]=(uint8_t)((((c)>>6)&0x3f)|0x80);
197            (s)[(i)++]=(uint8_t)(((c)&0x3f)|0x80);
198            return i;
199        }
200    } else if((uint32_t)(c)<=0x10ffff) {
201        if((i)+3<(length)) {
202            (s)[(i)++]=(uint8_t)(((c)>>18)|0xf0);
203            (s)[(i)++]=(uint8_t)((((c)>>12)&0x3f)|0x80);
204            (s)[(i)++]=(uint8_t)((((c)>>6)&0x3f)|0x80);
205            (s)[(i)++]=(uint8_t)(((c)&0x3f)|0x80);
206            return i;
207        }
208    }
209    /* c>0x10ffff or not enough space, write an error value */
210    if(pIsError!=NULL) {
211        *pIsError=TRUE;
212    } else {
213        length-=i;
214        if(length>0) {
215            int32_t offset;
216            if(length>3) {
217                length=3;
218            }
219            s+=i;
220            offset=0;
221            c=utf8_errorValue[length-1];
222            UTF8_APPEND_CHAR_UNSAFE(s, offset, c);
223            i=i+offset;
224        }
225    }
226    return i;
227}
228
229U_CAPI UChar32 U_EXPORT2
230utf8_prevCharSafeBody(const uint8_t *s, int32_t start, int32_t *pi, UChar32 c, UBool strict) {
231    int32_t i=*pi;
232    uint8_t b, count=1, shift=6;
233
234    if(!U8_IS_TRAIL(c)) { return errorValue(0, strict); }
235
236    /* extract value bits from the last trail byte */
237    c&=0x3f;
238
239    for(;;) {
240        if(i<=start) {
241            /* no lead byte at all */
242            return errorValue(0, strict);
243        }
244
245        /* read another previous byte */
246        b=s[--i];
247        if((uint8_t)(b-0x80)<0x7e) { /* 0x80<=b<0xfe */
248            if(b&0x40) {
249                /* lead byte, this will always end the loop */
250                uint8_t shouldCount=U8_COUNT_TRAIL_BYTES(b);
251
252                if(count==shouldCount) {
253                    /* set the new position */
254                    *pi=i;
255                    U8_MASK_LEAD_BYTE(b, count);
256                    c|=(UChar32)b<<shift;
257                    if(count>=4 || c>0x10ffff || c<utf8_minLegal[count] || (U_IS_SURROGATE(c) && strict!=-2) || (strict>0 && U_IS_UNICODE_NONCHAR(c))) {
258                        /* illegal sequence or (strict and non-character) */
259                        if(count>=4) {
260                            count=3;
261                        }
262                        c=errorValue(count, strict);
263                    } else {
264                        /* exit with correct c */
265                    }
266                } else {
267                    /* the lead byte does not match the number of trail bytes */
268                    /* only set the position to the lead byte if it would
269                       include the trail byte that we started with */
270                    if(count<shouldCount) {
271                        *pi=i;
272                        c=errorValue(count, strict);
273                    } else {
274                        c=errorValue(0, strict);
275                    }
276                }
277                break;
278            } else if(count<5) {
279                /* trail byte */
280                c|=(UChar32)(b&0x3f)<<shift;
281                ++count;
282                shift+=6;
283            } else {
284                /* more than 5 trail bytes is illegal */
285                c=errorValue(0, strict);
286                break;
287            }
288        } else {
289            /* single-byte character precedes trailing bytes */
290            c=errorValue(0, strict);
291            break;
292        }
293    }
294    return c;
295}
296
297U_CAPI int32_t U_EXPORT2
298utf8_back1SafeBody(const uint8_t *s, int32_t start, int32_t i) {
299    /* i had been decremented once before the function call */
300    int32_t I=i, Z;
301    uint8_t b;
302
303    /* read at most the 6 bytes s[Z] to s[i], inclusively */
304    if(I-5>start) {
305        Z=I-5;
306    } else {
307        Z=start;
308    }
309
310    /* return I if the sequence starting there is long enough to include i */
311    do {
312        b=s[I];
313        if((uint8_t)(b-0x80)>=0x7e) { /* not 0x80<=b<0xfe */
314            break;
315        } else if(b>=0xc0) {
316            if(U8_COUNT_TRAIL_BYTES(b)>=(i-I)) {
317                return I;
318            } else {
319                break;
320            }
321        }
322    } while(Z<=--I);
323
324    /* return i itself to be consistent with the FWD_1 macro */
325    return i;
326}
327