/src/icu/source/common/utf_impl.cpp

Source
// © 2016 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html
/*
******************************************************************************
*
*   Copyright (C) 1999-2012, International Business Machines
*   Corporation and others.  All Rights Reserved.
*
******************************************************************************
*   file name:  utf_impl.c
*   encoding:   UTF-8
*   tab size:   8 (not used)
*   indentation:4
*
*   created on: 1999sep13
*   created by: Markus W. Scherer
*
*   This file provides implementation functions for macros in the utfXX.h
*   that would otherwise be too long as macros.
*/

/* set import/export definitions */
#ifndef U_UTF8_IMPL
#   define U_UTF8_IMPL
#endif

#include "unicode/utypes.h"
#include "unicode/utf.h"
#include "unicode/utf8.h"
#include "unicode/utf_old.h"
#include "uassert.h"

/*
 * Table of the number of utf8 trail bytes, indexed by the lead byte.
 * Used by the deprecated macro UTF8_COUNT_TRAIL_BYTES, defined in utf_old.h
 *
 * The current macro, U8_COUNT_TRAIL_BYTES, does _not_ use this table.
 *
 * Note that this table cannot be removed, even if UTF8_COUNT_TRAIL_BYTES were
 * changed to no longer use it. References to the table from expansions of UTF8_COUNT_TRAIL_BYTES
 * may exist in old client code that must continue to run with newer icu library versions.
 *
 * This table could be replaced on many machines by
 * a few lines of assembler code using an
 * "index of first 0-bit from msb" instruction and
 * one or two more integer instructions.
 *
 * For example, on an i386, do something like
 * - MOV AL, leadByte
 * - NOT AL         (8-bit, leave b15..b8==0..0, reverse only b7..b0)
 * - MOV AH, 0
 * - BSR BX, AX     (16-bit)
 * - MOV AX, 6      (result)
 * - JZ finish      (ZF==1 if leadByte==0xff)
 * - SUB AX, BX (result)
 * -finish:
 * (BSR: Bit Scan Reverse, scans for a 1-bit, starting from the MSB)
 *
 * In Unicode, all UTF-8 byte sequences with more than 4 bytes are illegal;
 * lead bytes above 0xf4 are illegal.
 * We keep them in this table for skipping long ISO 10646-UTF-8 sequences.
 */
extern "C" U_EXPORT const uint8_t
utf8_countTrailBytes[256]={
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,

    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
    3, 3, 3, 3, 3,
    3, 3, 3,    /* illegal in Unicode */
    4, 4, 4, 4, /* illegal in Unicode */
    5, 5,       /* illegal in Unicode */
    0, 0        /* illegal bytes 0xfe and 0xff */
};

static const UChar32
utf8_minLegal[4]={ 0, 0x80, 0x800, 0x10000 };

static const UChar32
utf8_errorValue[6]={
    UTF8_ERROR_VALUE_1, UTF8_ERROR_VALUE_2, UTF_ERROR_VALUE, 0x10ffff,
    0x3ffffff, 0x7fffffff
};

static UChar32
errorValue(int32_t count, int8_t strict) {
    if(strict>=0) {
        return utf8_errorValue[count];
    } else if(strict==-3) {
        return 0xfffd;
    } else {
        return U_SENTINEL;
    }
}

/*
 * Handle the non-inline part of the U8_NEXT() and U8_NEXT_FFFD() macros
 * and their obsolete sibling UTF8_NEXT_CHAR_SAFE().
 *
 * U8_NEXT() supports NUL-terminated strings indicated via length<0.
 *
 * The "strict" parameter controls the error behavior:
 * <0  "Safe" behavior of U8_NEXT():
 *     -1: All illegal byte sequences yield U_SENTINEL=-1.
 *     -2: Same as -1, except for lenient treatment of surrogate code points as legal.
 *         Some implementations use this for roundtripping of
 *         Unicode 16-bit strings that are not well-formed UTF-16, that is, they
 *         contain unpaired surrogates.
 *     -3: All illegal byte sequences yield U+FFFD.
 *  0  Obsolete "safe" behavior of UTF8_NEXT_CHAR_SAFE(..., FALSE):
 *     All illegal byte sequences yield a positive code point such that this
 *     result code point would be encoded with the same number of bytes as
 *     the illegal sequence.
 * >0  Obsolete "strict" behavior of UTF8_NEXT_CHAR_SAFE(..., TRUE):
 *     Same as the obsolete "safe" behavior, but non-characters are also treated
 *     like illegal sequences.
 *
 * Note that a UBool is the same as an int8_t.
 */
U_CAPI UChar32 U_EXPORT2
utf8_nextCharSafeBody(const uint8_t *s, int32_t *pi, int32_t length, UChar32 c, UBool strict) {
    int32_t i=*pi;
    uint8_t count=U8_COUNT_TRAIL_BYTES(c);
    U_ASSERT(count <= 5); /* U8_COUNT_TRAIL_BYTES returns value 0...5 */
    if(i+count<=length || length<0) {
        uint8_t trail;

        U8_MASK_LEAD_BYTE(c, count);
        /* support NUL-terminated strings: do not read beyond the first non-trail byte */
        switch(count) {
        /* each branch falls through to the next one */
        case 0:
            /* count==0 for illegally leading trail bytes and the illegal bytes 0xfe and 0xff */
        case 5:
        case 4:
            /* count>=4 is always illegal: no more than 3 trail bytes in Unicode's UTF-8 */
            break;
        case 3:
            trail=s[i++]-0x80;
            c=(c<<6)|trail;
            /* c>=0x110 would result in code point>0x10ffff, outside Unicode */
            if(c>=0x110 || trail>0x3f) { break; }
            U_FALLTHROUGH;
        case 2:
            trail=s[i++]-0x80;
            c=(c<<6)|trail;
            /*
             * test for a surrogate d800..dfff unless we are lenient:
             * before the last (c<<6), a surrogate is c=360..37f
             */
            if(((c&0xffe0)==0x360 && strict!=-2) || trail>0x3f) { break; }
            U_FALLTHROUGH;
        case 1:
            trail=s[i++]-0x80;
            c=(c<<6)|trail;
            if(trail>0x3f) { break; }
            /* correct sequence - all trail bytes have (b7..b6)==(10) */
            if(c>=utf8_minLegal[count] &&
                    /* strict: forbid non-characters like U+fffe */
                    (strict<=0 || !U_IS_UNICODE_NONCHAR(c))) {
                *pi=i;
                return c;
            }
        /* no default branch to optimize switch()  - all values are covered */
        }
    } else {
        /* too few bytes left */
        count=length-i;
    }

    /* error handling */
    i=*pi;
    while(count>0 && U8_IS_TRAIL(s[i])) {
        ++i;
        --count;
    }
    c=errorValue(i-*pi, strict);
    *pi=i;
    return c;
}

U_CAPI int32_t U_EXPORT2
utf8_appendCharSafeBody(uint8_t *s, int32_t i, int32_t length, UChar32 c, UBool *pIsError) {
    if((uint32_t)(c)<=0x7ff) {
        if((i)+1<(length)) {
            (s)[(i)++]=(uint8_t)(((c)>>6)|0xc0);
            (s)[(i)++]=(uint8_t)(((c)&0x3f)|0x80);
            return i;
        }
    } else if((uint32_t)(c)<=0xffff) {
        /* Starting with Unicode 3.2, surrogate code points must not be encoded in UTF-8. */
        if((i)+2<(length) && !U_IS_SURROGATE(c)) {
            (s)[(i)++]=(uint8_t)(((c)>>12)|0xe0);
            (s)[(i)++]=(uint8_t)((((c)>>6)&0x3f)|0x80);
            (s)[(i)++]=(uint8_t)(((c)&0x3f)|0x80);
            return i;
        }
    } else if((uint32_t)(c)<=0x10ffff) {
        if((i)+3<(length)) {
            (s)[(i)++]=(uint8_t)(((c)>>18)|0xf0);
            (s)[(i)++]=(uint8_t)((((c)>>12)&0x3f)|0x80);
            (s)[(i)++]=(uint8_t)((((c)>>6)&0x3f)|0x80);
            (s)[(i)++]=(uint8_t)(((c)&0x3f)|0x80);
            return i;
        }
    }
    /* c>0x10ffff or not enough space, write an error value */
    if(pIsError!=NULL) {
        *pIsError=TRUE;
    } else {
        length-=i;
        if(length>0) {
            int32_t offset;
            if(length>3) {
                length=3;
            }
            s+=i;
            offset=0;
            c=utf8_errorValue[length-1];
            UTF8_APPEND_CHAR_UNSAFE(s, offset, c);
            i=i+offset;
        }
    }
    return i;
}

U_CAPI UChar32 U_EXPORT2
utf8_prevCharSafeBody(const uint8_t *s, int32_t start, int32_t *pi, UChar32 c, UBool strict) {
    int32_t i=*pi;
    uint8_t b, count=1, shift=6;

    if(!U8_IS_TRAIL(c)) { return errorValue(0, strict); }

    /* extract value bits from the last trail byte */
    c&=0x3f;

    for(;;) {
        if(i<=start) {
            /* no lead byte at all */
            return errorValue(0, strict);
        }

        /* read another previous byte */
        b=s[--i];
        if((uint8_t)(b-0x80)<0x7e) { /* 0x80<=b<0xfe */
            if(b&0x40) {
                /* lead byte, this will always end the loop */
                uint8_t shouldCount=U8_COUNT_TRAIL_BYTES(b);

                if(count==shouldCount) {
                    /* set the new position */
                    *pi=i;
                    U8_MASK_LEAD_BYTE(b, count);
                    c|=(UChar32)b<<shift;
                    if(count>=4 || c>0x10ffff || c<utf8_minLegal[count] || (U_IS_SURROGATE(c) && strict!=-2) || (strict>0 && U_IS_UNICODE_NONCHAR(c))) {
                        /* illegal sequence or (strict and non-character) */
                        if(count>=4) {
                            count=3;
                        }
                        c=errorValue(count, strict);
                    } else {
                        /* exit with correct c */
                    }
                } else {
                    /* the lead byte does not match the number of trail bytes */
                    /* only set the position to the lead byte if it would
                       include the trail byte that we started with */
                    if(count<shouldCount) {
                        *pi=i;
                        c=errorValue(count, strict);
                    } else {
                        c=errorValue(0, strict);
                    }
                }
                break;
            } else if(count<5) {
                /* trail byte */
                c|=(UChar32)(b&0x3f)<<shift;
                ++count;
                shift+=6;
            } else {
                /* more than 5 trail bytes is illegal */
                c=errorValue(0, strict);
                break;
            }
        } else {
            /* single-byte character precedes trailing bytes */
            c=errorValue(0, strict);
            break;
        }
    }
    return c;
}

U_CAPI int32_t U_EXPORT2
utf8_back1SafeBody(const uint8_t *s, int32_t start, int32_t i) {
    /* i had been decremented once before the function call */
    int32_t I=i, Z;
    uint8_t b;

    /* read at most the 6 bytes s[Z] to s[i], inclusively */
    if(I-5>start) {
        Z=I-5;
    } else {
        Z=start;
    }

    /* return I if the sequence starting there is long enough to include i */
    do {
        b=s[I];
        if((uint8_t)(b-0x80)>=0x7e) { /* not 0x80<=b<0xfe */
            break;
        } else if(b>=0xc0) {
            if(U8_COUNT_TRAIL_BYTES(b)>=(i-I)) {
                return I;
            } else {
                break;
            }
        }
    } while(Z<=--I);

    /* return i itself to be consistent with the FWD_1 macro */
    return i;
}

Coverage Report

Created: 2025-10-26 06:49

Line	Count	Source
1		// © 2016 and later: Unicode, Inc. and others.
2		// License & terms of use: http://www.unicode.org/copyright.html
3		/*
4		******************************************************************************
5		*
6		* Copyright (C) 1999-2012, International Business Machines
7		* Corporation and others. All Rights Reserved.
8		*
9		******************************************************************************
10		* file name: utf_impl.c
11		* encoding: UTF-8
12		* tab size: 8 (not used)
13		* indentation:4
14		*
15		* created on: 1999sep13
16		* created by: Markus W. Scherer
17		*
18		* This file provides implementation functions for macros in the utfXX.h
19		* that would otherwise be too long as macros.
20		*/
21
22		/* set import/export definitions */
23		#ifndef U_UTF8_IMPL
24		# define U_UTF8_IMPL
25		#endif
26
27		#include "unicode/utypes.h"
28		#include "unicode/utf.h"
29		#include "unicode/utf8.h"
30		#include "unicode/utf_old.h"
31		#include "uassert.h"
32
33		/*
34		* Table of the number of utf8 trail bytes, indexed by the lead byte.
35		* Used by the deprecated macro UTF8_COUNT_TRAIL_BYTES, defined in utf_old.h
36		*
37		* The current macro, U8_COUNT_TRAIL_BYTES, does _not_ use this table.
38		*
39		* Note that this table cannot be removed, even if UTF8_COUNT_TRAIL_BYTES were
40		* changed to no longer use it. References to the table from expansions of UTF8_COUNT_TRAIL_BYTES
41		* may exist in old client code that must continue to run with newer icu library versions.
42		*
43		* This table could be replaced on many machines by
44		* a few lines of assembler code using an
45		* "index of first 0-bit from msb" instruction and
46		* one or two more integer instructions.
47		*
48		* For example, on an i386, do something like
49		* - MOV AL, leadByte
50		* - NOT AL (8-bit, leave b15..b8==0..0, reverse only b7..b0)
51		* - MOV AH, 0
52		* - BSR BX, AX (16-bit)
53		* - MOV AX, 6 (result)
54		* - JZ finish (ZF==1 if leadByte==0xff)
55		* - SUB AX, BX (result)
56		* -finish:
57		* (BSR: Bit Scan Reverse, scans for a 1-bit, starting from the MSB)
58		*
59		* In Unicode, all UTF-8 byte sequences with more than 4 bytes are illegal;
60		* lead bytes above 0xf4 are illegal.
61		* We keep them in this table for skipping long ISO 10646-UTF-8 sequences.
62		*/
63		extern "C" U_EXPORT const uint8_t
64		utf8_countTrailBytes[256]={
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		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
69
70		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
71		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
72		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
73		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
74
75		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
76		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
77		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
78		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
79
80		1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
81		1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
82
83		2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
84		3, 3, 3, 3, 3,
85		3, 3, 3, /* illegal in Unicode */
86		4, 4, 4, 4, /* illegal in Unicode */
87		5, 5, /* illegal in Unicode */
88		0, 0 /* illegal bytes 0xfe and 0xff */
89		};
90
91		static const UChar32
92		utf8_minLegal[4]={ 0, 0x80, 0x800, 0x10000 };
93
94		static const UChar32
95		utf8_errorValue[6]={
96		UTF8_ERROR_VALUE_1, UTF8_ERROR_VALUE_2, UTF_ERROR_VALUE, 0x10ffff,
97		0x3ffffff, 0x7fffffff
98		};
99
100		static UChar32
101	0	errorValue(int32_t count, int8_t strict) {
102	0	if(strict>=0) {
103	0	return utf8_errorValue[count];
104	0	} else if(strict==-3) {
105	0	return 0xfffd;
106	0	} else {
107	0	return U_SENTINEL;
108	0	}
109	0	}
110
111		/*
112		* Handle the non-inline part of the U8_NEXT() and U8_NEXT_FFFD() macros
113		* and their obsolete sibling UTF8_NEXT_CHAR_SAFE().
114		*
115		* U8_NEXT() supports NUL-terminated strings indicated via length<0.
116		*
117		* The "strict" parameter controls the error behavior:
118		* <0 "Safe" behavior of U8_NEXT():
119		* -1: All illegal byte sequences yield U_SENTINEL=-1.
120		* -2: Same as -1, except for lenient treatment of surrogate code points as legal.
121		* Some implementations use this for roundtripping of
122		* Unicode 16-bit strings that are not well-formed UTF-16, that is, they
123		* contain unpaired surrogates.
124		* -3: All illegal byte sequences yield U+FFFD.
125		* 0 Obsolete "safe" behavior of UTF8_NEXT_CHAR_SAFE(..., FALSE):
126		* All illegal byte sequences yield a positive code point such that this
127		* result code point would be encoded with the same number of bytes as
128		* the illegal sequence.
129		* >0 Obsolete "strict" behavior of UTF8_NEXT_CHAR_SAFE(..., TRUE):
130		* Same as the obsolete "safe" behavior, but non-characters are also treated
131		* like illegal sequences.
132		*
133		* Note that a UBool is the same as an int8_t.
134		*/
135		U_CAPI UChar32 U_EXPORT2
136	0	utf8_nextCharSafeBody(const uint8_t s, int32_t pi, int32_t length, UChar32 c, UBool strict) {
137	0	int32_t i=*pi;
138	0	uint8_t count=U8_COUNT_TRAIL_BYTES(c);
139	0	U_ASSERT(count <= 5); /* U8_COUNT_TRAIL_BYTES returns value 0...5 */
140	0	if(i+count<=length \|\| length<0) {
141	0	uint8_t trail;
142
143	0	U8_MASK_LEAD_BYTE(c, count);
144		/* support NUL-terminated strings: do not read beyond the first non-trail byte */
145	0	switch(count) {
146		/* each branch falls through to the next one */
147	0	case 0:
148		/* count==0 for illegally leading trail bytes and the illegal bytes 0xfe and 0xff */
149	0	case 5:
150	0	case 4:
151		/* count>=4 is always illegal: no more than 3 trail bytes in Unicode's UTF-8 */
152	0	break;
153	0	case 3:
154	0	trail=s[i++]-0x80;
155	0	c=(c<<6)\|trail;
156		/* c>=0x110 would result in code point>0x10ffff, outside Unicode */
157	0	if(c>=0x110 \|\| trail>0x3f) { break; }
158	0	U_FALLTHROUGH;
159	0	case 2:
160	0	trail=s[i++]-0x80;
161	0	c=(c<<6)\|trail;
162		/*
163		* test for a surrogate d800..dfff unless we are lenient:
164		* before the last (c<<6), a surrogate is c=360..37f
165		*/
166	0	if(((c&0xffe0)==0x360 && strict!=-2) \|\| trail>0x3f) { break; }
167	0	U_FALLTHROUGH;
168	0	case 1:
169	0	trail=s[i++]-0x80;
170	0	c=(c<<6)\|trail;
171	0	if(trail>0x3f) { break; }
172		/* correct sequence - all trail bytes have (b7..b6)==(10) */
173	0	if(c>=utf8_minLegal[count] &&
174		/* strict: forbid non-characters like U+fffe */
175	0	(strict<=0 \|\| !U_IS_UNICODE_NONCHAR(c))) {
176	0	*pi=i;
177	0	return c;
178	0	}
179		/* no default branch to optimize switch() - all values are covered */
180	0	}
181	0	} else {
182		/* too few bytes left */
183	0	count=length-i;
184	0	}
185
186		/* error handling */
187	0	i=*pi;
188	0	while(count>0 && U8_IS_TRAIL(s[i])) {
189	0	++i;
190	0	--count;
191	0	}
192	0	c=errorValue(i-*pi, strict);
193	0	*pi=i;
194	0	return c;
195	0	}
196
197		U_CAPI int32_t U_EXPORT2
198	0	utf8_appendCharSafeBody(uint8_t s, int32_t i, int32_t length, UChar32 c, UBool pIsError) {
199	0	if((uint32_t)(c)<=0x7ff) {
200	0	if((i)+1<(length)) {
201	0	(s)[(i)++]=(uint8_t)(((c)>>6)\|0xc0);
202	0	(s)[(i)++]=(uint8_t)(((c)&0x3f)\|0x80);
203	0	return i;
204	0	}
205	0	} else if((uint32_t)(c)<=0xffff) {
206		/* Starting with Unicode 3.2, surrogate code points must not be encoded in UTF-8. */
207	0	if((i)+2<(length) && !U_IS_SURROGATE(c)) {
208	0	(s)[(i)++]=(uint8_t)(((c)>>12)\|0xe0);
209	0	(s)[(i)++]=(uint8_t)((((c)>>6)&0x3f)\|0x80);
210	0	(s)[(i)++]=(uint8_t)(((c)&0x3f)\|0x80);
211	0	return i;
212	0	}
213	0	} else if((uint32_t)(c)<=0x10ffff) {
214	0	if((i)+3<(length)) {
215	0	(s)[(i)++]=(uint8_t)(((c)>>18)\|0xf0);
216	0	(s)[(i)++]=(uint8_t)((((c)>>12)&0x3f)\|0x80);
217	0	(s)[(i)++]=(uint8_t)((((c)>>6)&0x3f)\|0x80);
218	0	(s)[(i)++]=(uint8_t)(((c)&0x3f)\|0x80);
219	0	return i;
220	0	}
221	0	}
222		/* c>0x10ffff or not enough space, write an error value */
223	0	if(pIsError!=NULL) {
224	0	*pIsError=TRUE;
225	0	} else {
226	0	length-=i;
227	0	if(length>0) {
228	0	int32_t offset;
229	0	if(length>3) {
230	0	length=3;
231	0	}
232	0	s+=i;
233	0	offset=0;
234	0	c=utf8_errorValue[length-1];
235	0	UTF8_APPEND_CHAR_UNSAFE(s, offset, c);
236	0	i=i+offset;
237	0	}
238	0	}
239	0	return i;
240	0	}
241
242		U_CAPI UChar32 U_EXPORT2
243	0	utf8_prevCharSafeBody(const uint8_t s, int32_t start, int32_t pi, UChar32 c, UBool strict) {
244	0	int32_t i=*pi;
245	0	uint8_t b, count=1, shift=6;
246
247	0	if(!U8_IS_TRAIL(c)) { return errorValue(0, strict); }
248
249		/* extract value bits from the last trail byte */
250	0	c&=0x3f;
251
252	0	for(;;) {
253	0	if(i<=start) {
254		/* no lead byte at all */
255	0	return errorValue(0, strict);
256	0	}
257
258		/* read another previous byte */
259	0	b=s[--i];
260	0	if((uint8_t)(b-0x80)<0x7e) { /* 0x80<=b<0xfe */
261	0	if(b&0x40) {
262		/* lead byte, this will always end the loop */
263	0	uint8_t shouldCount=U8_COUNT_TRAIL_BYTES(b);
264
265	0	if(count==shouldCount) {
266		/* set the new position */
267	0	*pi=i;
268	0	U8_MASK_LEAD_BYTE(b, count);
269	0	c\|=(UChar32)b<<shift;
270	0	if(count>=4 \|\| c>0x10ffff \|\| c<utf8_minLegal[count] \|\| (U_IS_SURROGATE(c) && strict!=-2) \|\| (strict>0 && U_IS_UNICODE_NONCHAR(c))) {
271		/* illegal sequence or (strict and non-character) */
272	0	if(count>=4) {
273	0	count=3;
274	0	}
275	0	c=errorValue(count, strict);
276	0	} else {
277		/* exit with correct c */
278	0	}
279	0	} else {
280		/* the lead byte does not match the number of trail bytes */
281		/* only set the position to the lead byte if it would
282		include the trail byte that we started with */
283	0	if(count<shouldCount) {
284	0	*pi=i;
285	0	c=errorValue(count, strict);
286	0	} else {
287	0	c=errorValue(0, strict);
288	0	}
289	0	}
290	0	break;
291	0	} else if(count<5) {
292		/* trail byte */
293	0	c\|=(UChar32)(b&0x3f)<<shift;
294	0	++count;
295	0	shift+=6;
296	0	} else {
297		/* more than 5 trail bytes is illegal */
298	0	c=errorValue(0, strict);
299	0	break;
300	0	}
301	0	} else {
302		/* single-byte character precedes trailing bytes */
303	0	c=errorValue(0, strict);
304	0	break;
305	0	}
306	0	}
307	0	return c;
308	0	}
309
310		U_CAPI int32_t U_EXPORT2
311	0	utf8_back1SafeBody(const uint8_t *s, int32_t start, int32_t i) {
312		/* i had been decremented once before the function call */
313	0	int32_t I=i, Z;
314	0	uint8_t b;
315
316		/* read at most the 6 bytes s[Z] to s[i], inclusively */
317	0	if(I-5>start) {
318	0	Z=I-5;
319	0	} else {
320	0	Z=start;
321	0	}
322
323		/* return I if the sequence starting there is long enough to include i */
324	0	do {
325	0	b=s[I];
326	0	if((uint8_t)(b-0x80)>=0x7e) { /* not 0x80<=b<0xfe */
327	0	break;
328	0	} else if(b>=0xc0) {
329	0	if(U8_COUNT_TRAIL_BYTES(b)>=(i-I)) {
330	0	return I;
331	0	} else {
332	0	break;
333	0	}
334	0	}
335	0	} while(Z<=--I);
336
337		/* return i itself to be consistent with the FWD_1 macro */
338	0	return i;
339	0	}