wchar.c

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/*-------------------------------------------------------------------------
 *
 * wchar.c
 *    Functions for working with multibyte characters in various encodings.
 *
 * Portions Copyright (c) 1998-2025, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/common/wchar.c
 *
 *-------------------------------------------------------------------------
 */
#include "c.h"
 
#include <limits.h>
 
#include "mb/pg_wchar.h"
#include "utils/ascii.h"
 
 
/*
 * In today's multibyte encodings other than UTF8, this two-byte sequence
 * ensures pg_encoding_mblen() == 2 && pg_encoding_verifymbstr() == 0.
 *
 * For historical reasons, several verifychar implementations opt to reject
 * this pair specifically.  Byte pair range constraints, in encoding
 * originator documentation, always excluded this pair.  No core conversion
 * could translate it.  However, longstanding verifychar implementations
 * accepted any non-NUL byte.  big5_to_euc_tw and big5_to_mic even translate
 * pairs not valid per encoding originator documentation.  To avoid tightening
 * core or non-core conversions in a security patch, we sought this one pair.
 *
 * PQescapeString() historically used spaces for BYTE1; many other values
 * could suffice for BYTE1.
 */
#define NONUTF8_INVALID_BYTE0 (0x8d)
#define NONUTF8_INVALID_BYTE1 (' ')
 
 
/*
 * Operations on multi-byte encodings are driven by a table of helper
 * functions.
 *
 * To add an encoding support, define mblen(), dsplen(), verifychar() and
 * verifystr() for the encoding.  For server-encodings, also define mb2wchar()
 * and wchar2mb() conversion functions.
 *
 * These functions generally assume that their input is validly formed.
 * The "verifier" functions, further down in the file, have to be more
 * paranoid.
 *
 * We expect that mblen() does not need to examine more than the first byte
 * of the character to discover the correct length.  GB18030 is an exception
 * to that rule, though, as it also looks at second byte.  But even that
 * behaves in a predictable way, if you only pass the first byte: it will
 * treat 4-byte encoded characters as two 2-byte encoded characters, which is
 * good enough for all current uses.
 *
 * Note: for the display output of psql to work properly, the return values
 * of the dsplen functions must conform to the Unicode standard. In particular
 * the NUL character is zero width and control characters are generally
 * width -1. It is recommended that non-ASCII encodings refer their ASCII
 * subset to the ASCII routines to ensure consistency.
 */
 
/*
 * SQL/ASCII
 */
static int
pg_ascii2wchar_with_len(const unsigned char *from, pg_wchar *to, int len)
{
    int         cnt = 0;
 
    while (len > 0 && *from)
    {
        *to++ = *from++;
        len--;
        cnt++;
    }
    *to = 0;
    return cnt;
}
 
static int
pg_ascii_mblen(const unsigned char *s)
{
    return 1;
}
 
static int
pg_ascii_dsplen(const unsigned char *s)
{
    if (*s == '\0')
        return 0;
    if (*s < 0x20 || *s == 0x7f)
        return -1;
 
    return 1;
}
 
/*
 * EUC
 */
static int
pg_euc2wchar_with_len(const unsigned char *from, pg_wchar *to, int len)
{
    int         cnt = 0;
 
    while (len > 0 && *from)
    {
        if (*from == SS2 && len >= 2)   /* JIS X 0201 (so called "1 byte
                                         * KANA") */
        {
            from++;
            *to = (SS2 << 8) | *from++;
            len -= 2;
        }
        else if (*from == SS3 && len >= 3)  /* JIS X 0212 KANJI */
        {
            from++;
            *to = (SS3 << 16) | (*from++ << 8);
            *to |= *from++;
            len -= 3;
        }
        else if (IS_HIGHBIT_SET(*from) && len >= 2) /* JIS X 0208 KANJI */
        {
            *to = *from++ << 8;
            *to |= *from++;
            len -= 2;
        }
        else                    /* must be ASCII */
        {
            *to = *from++;
            len--;
        }
        to++;
        cnt++;
    }
    *to = 0;
    return cnt;
}
 
static inline int
pg_euc_mblen(const unsigned char *s)
{
    int         len;
 
    if (*s == SS2)
        len = 2;
    else if (*s == SS3)
        len = 3;
    else if (IS_HIGHBIT_SET(*s))
        len = 2;
    else
        len = 1;
    return len;
}
 
static inline int
pg_euc_dsplen(const unsigned char *s)
{
    int         len;
 
    if (*s == SS2)
        len = 2;
    else if (*s == SS3)
        len = 2;
    else if (IS_HIGHBIT_SET(*s))
        len = 2;
    else
        len = pg_ascii_dsplen(s);
    return len;
}
 
/*
 * EUC_JP
 */
static int
pg_eucjp2wchar_with_len(const unsigned char *from, pg_wchar *to, int len)
{
    return pg_euc2wchar_with_len(from, to, len);
}
 
static int
pg_eucjp_mblen(const unsigned char *s)
{
    return pg_euc_mblen(s);
}
 
static int
pg_eucjp_dsplen(const unsigned char *s)
{
    int         len;
 
    if (*s == SS2)
        len = 1;
    else if (*s == SS3)
        len = 2;
    else if (IS_HIGHBIT_SET(*s))
        len = 2;
    else
        len = pg_ascii_dsplen(s);
    return len;
}
 
/*
 * EUC_KR
 */
static int
pg_euckr2wchar_with_len(const unsigned char *from, pg_wchar *to, int len)
{
    return pg_euc2wchar_with_len(from, to, len);
}
 
static int
pg_euckr_mblen(const unsigned char *s)
{
    return pg_euc_mblen(s);
}
 
static int
pg_euckr_dsplen(const unsigned char *s)
{
    return pg_euc_dsplen(s);
}
 
/*
 * EUC_CN
 *
 */
static int
pg_euccn2wchar_with_len(const unsigned char *from, pg_wchar *to, int len)
{
    int         cnt = 0;
 
    while (len > 0 && *from)
    {
        if (*from == SS2 && len >= 3)   /* code set 2 (unused?) */
        {
            from++;
            *to = (SS2 << 16) | (*from++ << 8);
            *to |= *from++;
            len -= 3;
        }
        else if (*from == SS3 && len >= 3)  /* code set 3 (unused ?) */
        {
            from++;
            *to = (SS3 << 16) | (*from++ << 8);
            *to |= *from++;
            len -= 3;
        }
        else if (IS_HIGHBIT_SET(*from) && len >= 2) /* code set 1 */
        {
            *to = *from++ << 8;
            *to |= *from++;
            len -= 2;
        }
        else
        {
            *to = *from++;
            len--;
        }
        to++;
        cnt++;
    }
    *to = 0;
    return cnt;
}
 
static int
pg_euccn_mblen(const unsigned char *s)
{
    int         len;
 
    if (IS_HIGHBIT_SET(*s))
        len = 2;
    else
        len = 1;
    return len;
}
 
static int
pg_euccn_dsplen(const unsigned char *s)
{
    int         len;
 
    if (IS_HIGHBIT_SET(*s))
        len = 2;
    else
        len = pg_ascii_dsplen(s);
    return len;
}
 
/*
 * EUC_TW
 *
 */
static int
pg_euctw2wchar_with_len(const unsigned char *from, pg_wchar *to, int len)
{
    int         cnt = 0;
 
    while (len > 0 && *from)
    {
        if (*from == SS2 && len >= 4)   /* code set 2 */
        {
            from++;
            *to = (((uint32) SS2) << 24) | (*from++ << 16);
            *to |= *from++ << 8;
            *to |= *from++;
            len -= 4;
        }
        else if (*from == SS3 && len >= 3)  /* code set 3 (unused?) */
        {
            from++;
            *to = (SS3 << 16) | (*from++ << 8);
            *to |= *from++;
            len -= 3;
        }
        else if (IS_HIGHBIT_SET(*from) && len >= 2) /* code set 2 */
        {
            *to = *from++ << 8;
            *to |= *from++;
            len -= 2;
        }
        else
        {
            *to = *from++;
            len--;
        }
        to++;
        cnt++;
    }
    *to = 0;
    return cnt;
}
 
static int
pg_euctw_mblen(const unsigned char *s)
{
    int         len;
 
    if (*s == SS2)
        len = 4;
    else if (*s == SS3)
        len = 3;
    else if (IS_HIGHBIT_SET(*s))
        len = 2;
    else
        len = 1;
    return len;
}
 
static int
pg_euctw_dsplen(const unsigned char *s)
{
    int         len;
 
    if (*s == SS2)
        len = 2;
    else if (*s == SS3)
        len = 2;
    else if (IS_HIGHBIT_SET(*s))
        len = 2;
    else
        len = pg_ascii_dsplen(s);
    return len;
}
 
/*
 * Convert pg_wchar to EUC_* encoding.
 * caller must allocate enough space for "to", including a trailing zero!
 * len: length of from.
 * "from" not necessarily null terminated.
 */
static int
pg_wchar2euc_with_len(const pg_wchar *from, unsigned char *to, int len)
{
    int         cnt = 0;
 
    while (len > 0 && *from)
    {
        unsigned char c;
 
        if ((c = (*from >> 24)))
        {
            *to++ = c;
            *to++ = (*from >> 16) & 0xff;
            *to++ = (*from >> 8) & 0xff;
            *to++ = *from & 0xff;
            cnt += 4;
        }
        else if ((c = (*from >> 16)))
        {
            *to++ = c;
            *to++ = (*from >> 8) & 0xff;
            *to++ = *from & 0xff;
            cnt += 3;
        }
        else if ((c = (*from >> 8)))
        {
            *to++ = c;
            *to++ = *from & 0xff;
            cnt += 2;
        }
        else
        {
            *to++ = *from;
            cnt++;
        }
        from++;
        len--;
    }
    *to = 0;
    return cnt;
}
 
 
/*
 * JOHAB
 */
static int
pg_johab_mblen(const unsigned char *s)
{
    return pg_euc_mblen(s);
}
 
static int
pg_johab_dsplen(const unsigned char *s)
{
    return pg_euc_dsplen(s);
}
 
/*
 * convert UTF8 string to pg_wchar (UCS-4)
 * caller must allocate enough space for "to", including a trailing zero!
 * len: length of from.
 * "from" not necessarily null terminated.
 */
static int
pg_utf2wchar_with_len(const unsigned char *from, pg_wchar *to, int len)
{
    int         cnt = 0;
    uint32      c1,
                c2,
                c3,
                c4;
 
    while (len > 0 && *from)
    {
        if ((*from & 0x80) == 0)
        {
            *to = *from++;
            len--;
        }
        else if ((*from & 0xe0) == 0xc0)
        {
            if (len < 2)
                break;          /* drop trailing incomplete char */
            c1 = *from++ & 0x1f;
            c2 = *from++ & 0x3f;
            *to = (c1 << 6) | c2;
            len -= 2;
        }
        else if ((*from & 0xf0) == 0xe0)
        {
            if (len < 3)
                break;          /* drop trailing incomplete char */
            c1 = *from++ & 0x0f;
            c2 = *from++ & 0x3f;
            c3 = *from++ & 0x3f;
            *to = (c1 << 12) | (c2 << 6) | c3;
            len -= 3;
        }
        else if ((*from & 0xf8) == 0xf0)
        {
            if (len < 4)
                break;          /* drop trailing incomplete char */
            c1 = *from++ & 0x07;
            c2 = *from++ & 0x3f;
            c3 = *from++ & 0x3f;
            c4 = *from++ & 0x3f;
            *to = (c1 << 18) | (c2 << 12) | (c3 << 6) | c4;
            len -= 4;
        }
        else
        {
            /* treat a bogus char as length 1; not ours to raise error */
            *to = *from++;
            len--;
        }
        to++;
        cnt++;
    }
    *to = 0;
    return cnt;
}
 
 
/*
 * Trivial conversion from pg_wchar to UTF-8.
 * caller should allocate enough space for "to"
 * len: length of from.
 * "from" not necessarily null terminated.
 */
static int
pg_wchar2utf_with_len(const pg_wchar *from, unsigned char *to, int len)
{
    int         cnt = 0;
 
    while (len > 0 && *from)
    {
        int         char_len;
 
        unicode_to_utf8(*from, to);
        char_len = pg_utf_mblen(to);
        cnt += char_len;
        to += char_len;
        from++;
        len--;
    }
    *to = 0;
    return cnt;
}
 
/*
 * Return the byte length of a UTF8 character pointed to by s
 *
 * Note: in the current implementation we do not support UTF8 sequences
 * of more than 4 bytes; hence do NOT return a value larger than 4.
 * We return "1" for any leading byte that is either flat-out illegal or
 * indicates a length larger than we support.
 *
 * pg_utf2wchar_with_len(), utf8_to_unicode(), pg_utf8_islegal(), and perhaps
 * other places would need to be fixed to change this.
 */
int
pg_utf_mblen(const unsigned char *s)
{
    int         len;
 
    if ((*s & 0x80) == 0)
        len = 1;
    else if ((*s & 0xe0) == 0xc0)
        len = 2;
    else if ((*s & 0xf0) == 0xe0)
        len = 3;
    else if ((*s & 0xf8) == 0xf0)
        len = 4;
#ifdef NOT_USED
    else if ((*s & 0xfc) == 0xf8)
        len = 5;
    else if ((*s & 0xfe) == 0xfc)
        len = 6;
#endif
    else
        len = 1;
    return len;
}
 
/*
 * This is an implementation of wcwidth() and wcswidth() as defined in
 * "The Single UNIX Specification, Version 2, The Open Group, 1997"
 * <http://www.unix.org/online.html>
 *
 * Markus Kuhn -- 2001-09-08 -- public domain
 *
 * customised for PostgreSQL
 *
 * original available at : http://www.cl.cam.ac.uk/~mgk25/ucs/wcwidth.c
 */
 
struct mbinterval
{
    unsigned int first;
    unsigned int last;
};
 
/* auxiliary function for binary search in interval table */
static int
mbbisearch(pg_wchar ucs, const struct mbinterval *table, int max)
{
    int         min = 0;
    int         mid;
 
    if (ucs < table[0].first || ucs > table[max].last)
        return 0;
    while (max >= min)
    {
        mid = (min + max) / 2;
        if (ucs > table[mid].last)
            min = mid + 1;
        else if (ucs < table[mid].first)
            max = mid - 1;
        else
            return 1;
    }
 
    return 0;
}
 
 
/* The following functions define the column width of an ISO 10646
 * character as follows:
 *
 *    - The null character (U+0000) has a column width of 0.
 *
 *    - Other C0/C1 control characters and DEL will lead to a return
 *      value of -1.
 *
 *    - Non-spacing and enclosing combining characters (general
 *      category code Mn, Me or Cf in the Unicode database) have a
 *      column width of 0.
 *
 *    - Spacing characters in the East Asian Wide (W) or East Asian
 *      FullWidth (F) category as defined in Unicode Technical
 *      Report #11 have a column width of 2.
 *
 *    - All remaining characters (including all printable
 *      ISO 8859-1 and WGL4 characters, Unicode control characters,
 *      etc.) have a column width of 1.
 *
 * This implementation assumes that wchar_t characters are encoded
 * in ISO 10646.
 */
 
static int
ucs_wcwidth(pg_wchar ucs)
{
#include "common/unicode_nonspacing_table.h"
#include "common/unicode_east_asian_fw_table.h"
 
    /* test for 8-bit control characters */
    if (ucs == 0)
        return 0;
 
    if (ucs < 0x20 || (ucs >= 0x7f && ucs < 0xa0) || ucs > 0x0010ffff)
        return -1;
 
    /*
     * binary search in table of non-spacing characters
     *
     * XXX: In the official Unicode sources, it is possible for a character to
     * be described as both non-spacing and wide at the same time. As of
     * Unicode 13.0, treating the non-spacing property as the determining
     * factor for display width leads to the correct behavior, so do that
     * search first.
     */
    if (mbbisearch(ucs, nonspacing,
                   sizeof(nonspacing) / sizeof(struct mbinterval) - 1))
        return 0;
 
    /* binary search in table of wide characters */
    if (mbbisearch(ucs, east_asian_fw,
                   sizeof(east_asian_fw) / sizeof(struct mbinterval) - 1))
        return 2;
 
    return 1;
}
 
static int
pg_utf_dsplen(const unsigned char *s)
{
    return ucs_wcwidth(utf8_to_unicode(s));
}
 
/*
 * convert mule internal code to pg_wchar
 * caller should allocate enough space for "to"
 * len: length of from.
 * "from" not necessarily null terminated.
 */
static int
pg_mule2wchar_with_len(const unsigned char *from, pg_wchar *to, int len)
{
    int         cnt = 0;
 
    while (len > 0 && *from)
    {
        if (IS_LC1(*from) && len >= 2)
        {
            *to = *from++ << 16;
            *to |= *from++;
            len -= 2;
        }
        else if (IS_LCPRV1(*from) && len >= 3)
        {
            from++;
            *to = *from++ << 16;
            *to |= *from++;
            len -= 3;
        }
        else if (IS_LC2(*from) && len >= 3)
        {
            *to = *from++ << 16;
            *to |= *from++ << 8;
            *to |= *from++;
            len -= 3;
        }
        else if (IS_LCPRV2(*from) && len >= 4)
        {
            from++;
            *to = *from++ << 16;
            *to |= *from++ << 8;
            *to |= *from++;
            len -= 4;
        }
        else
        {                       /* assume ASCII */
            *to = (unsigned char) *from++;
            len--;
        }
        to++;
        cnt++;
    }
    *to = 0;
    return cnt;
}
 
/*
 * convert pg_wchar to mule internal code
 * caller should allocate enough space for "to"
 * len: length of from.
 * "from" not necessarily null terminated.
 */
static int
pg_wchar2mule_with_len(const pg_wchar *from, unsigned char *to, int len)
{
    int         cnt = 0;
 
    while (len > 0 && *from)
    {
        unsigned char lb;
 
        lb = (*from >> 16) & 0xff;
        if (IS_LC1(lb))
        {
            *to++ = lb;
            *to++ = *from & 0xff;
            cnt += 2;
        }
        else if (IS_LC2(lb))
        {
            *to++ = lb;
            *to++ = (*from >> 8) & 0xff;
            *to++ = *from & 0xff;
            cnt += 3;
        }
        else if (IS_LCPRV1_A_RANGE(lb))
        {
            *to++ = LCPRV1_A;
            *to++ = lb;
            *to++ = *from & 0xff;
            cnt += 3;
        }
        else if (IS_LCPRV1_B_RANGE(lb))
        {
            *to++ = LCPRV1_B;
            *to++ = lb;
            *to++ = *from & 0xff;
            cnt += 3;
        }
        else if (IS_LCPRV2_A_RANGE(lb))
        {
            *to++ = LCPRV2_A;
            *to++ = lb;
            *to++ = (*from >> 8) & 0xff;
            *to++ = *from & 0xff;
            cnt += 4;
        }
        else if (IS_LCPRV2_B_RANGE(lb))
        {
            *to++ = LCPRV2_B;
            *to++ = lb;
            *to++ = (*from >> 8) & 0xff;
            *to++ = *from & 0xff;
            cnt += 4;
        }
        else
        {
            *to++ = *from & 0xff;
            cnt += 1;
        }
        from++;
        len--;
    }
    *to = 0;
    return cnt;
}
 
/* exported for direct use by conv.c */
int
pg_mule_mblen(const unsigned char *s)
{
    int         len;
 
    if (IS_LC1(*s))
        len = 2;
    else if (IS_LCPRV1(*s))
        len = 3;
    else if (IS_LC2(*s))
        len = 3;
    else if (IS_LCPRV2(*s))
        len = 4;
    else
        len = 1;                /* assume ASCII */
    return len;
}
 
static int
pg_mule_dsplen(const unsigned char *s)
{
    int         len;
 
    /*
     * Note: it's not really appropriate to assume that all multibyte charsets
     * are double-wide on screen.  But this seems an okay approximation for
     * the MULE charsets we currently support.
     */
 
    if (IS_LC1(*s))
        len = 1;
    else if (IS_LCPRV1(*s))
        len = 1;
    else if (IS_LC2(*s))
        len = 2;
    else if (IS_LCPRV2(*s))
        len = 2;
    else
        len = 1;                /* assume ASCII */
 
    return len;
}
 
/*
 * ISO8859-1
 */
static int
pg_latin12wchar_with_len(const unsigned char *from, pg_wchar *to, int len)
{
    int         cnt = 0;
 
    while (len > 0 && *from)
    {
        *to++ = *from++;
        len--;
        cnt++;
    }
    *to = 0;
    return cnt;
}
 
/*
 * Trivial conversion from pg_wchar to single byte encoding. Just ignores
 * high bits.
 * caller should allocate enough space for "to"
 * len: length of from.
 * "from" not necessarily null terminated.
 */
static int
pg_wchar2single_with_len(const pg_wchar *from, unsigned char *to, int len)
{
    int         cnt = 0;
 
    while (len > 0 && *from)
    {
        *to++ = *from++;
        len--;
        cnt++;
    }
    *to = 0;
    return cnt;
}
 
static int
pg_latin1_mblen(const unsigned char *s)
{
    return 1;
}
 
static int
pg_latin1_dsplen(const unsigned char *s)
{
    return pg_ascii_dsplen(s);
}
 
/*
 * SJIS
 */
static int
pg_sjis_mblen(const unsigned char *s)
{
    int         len;
 
    if (*s >= 0xa1 && *s <= 0xdf)
        len = 1;                /* 1 byte kana? */
    else if (IS_HIGHBIT_SET(*s))
        len = 2;                /* kanji? */
    else
        len = 1;                /* should be ASCII */
    return len;
}
 
static int
pg_sjis_dsplen(const unsigned char *s)
{
    int         len;
 
    if (*s >= 0xa1 && *s <= 0xdf)
        len = 1;                /* 1 byte kana? */
    else if (IS_HIGHBIT_SET(*s))
        len = 2;                /* kanji? */
    else
        len = pg_ascii_dsplen(s);   /* should be ASCII */
    return len;
}
 
/*
 * Big5
 */
static int
pg_big5_mblen(const unsigned char *s)
{
    int         len;
 
    if (IS_HIGHBIT_SET(*s))
        len = 2;                /* kanji? */
    else
        len = 1;                /* should be ASCII */
    return len;
}
 
static int
pg_big5_dsplen(const unsigned char *s)
{
    int         len;
 
    if (IS_HIGHBIT_SET(*s))
        len = 2;                /* kanji? */
    else
        len = pg_ascii_dsplen(s);   /* should be ASCII */
    return len;
}
 
/*
 * GBK
 */
static int
pg_gbk_mblen(const unsigned char *s)
{
    int         len;
 
    if (IS_HIGHBIT_SET(*s))
        len = 2;                /* kanji? */
    else
        len = 1;                /* should be ASCII */
    return len;
}
 
static int
pg_gbk_dsplen(const unsigned char *s)
{
    int         len;
 
    if (IS_HIGHBIT_SET(*s))
        len = 2;                /* kanji? */
    else
        len = pg_ascii_dsplen(s);   /* should be ASCII */
    return len;
}
 
/*
 * UHC
 */
static int
pg_uhc_mblen(const unsigned char *s)
{
    int         len;
 
    if (IS_HIGHBIT_SET(*s))
        len = 2;                /* 2byte? */
    else
        len = 1;                /* should be ASCII */
    return len;
}
 
static int
pg_uhc_dsplen(const unsigned char *s)
{
    int         len;
 
    if (IS_HIGHBIT_SET(*s))
        len = 2;                /* 2byte? */
    else
        len = pg_ascii_dsplen(s);   /* should be ASCII */
    return len;
}
 
/*
 * GB18030
 *  Added by Bill Huang <bhuang@redhat.com>,<bill_huanghb@ybb.ne.jp>
 */
 
/*
 * Unlike all other mblen() functions, this also looks at the second byte of
 * the input.  However, if you only pass the first byte of a multi-byte
 * string, and \0 as the second byte, this still works in a predictable way:
 * a 4-byte character will be reported as two 2-byte characters.  That's
 * enough for all current uses, as a client-only encoding.  It works that
 * way, because in any valid 4-byte GB18030-encoded character, the third and
 * fourth byte look like a 2-byte encoded character, when looked at
 * separately.
 */
static int
pg_gb18030_mblen(const unsigned char *s)
{
    int         len;
 
    if (!IS_HIGHBIT_SET(*s))
        len = 1;                /* ASCII */
    else if (*(s + 1) >= 0x30 && *(s + 1) <= 0x39)
        len = 4;
    else
        len = 2;
    return len;
}
 
static int
pg_gb18030_dsplen(const unsigned char *s)
{
    int         len;
 
    if (IS_HIGHBIT_SET(*s))
        len = 2;
    else
        len = pg_ascii_dsplen(s);   /* ASCII */
    return len;
}
 
/*
 *-------------------------------------------------------------------
 * multibyte sequence validators
 *
 * The verifychar functions accept "s", a pointer to the first byte of a
 * string, and "len", the remaining length of the string.  If there is a
 * validly encoded character beginning at *s, return its length in bytes;
 * else return -1.
 *
 * The verifystr functions also accept "s", a pointer to a string and "len",
 * the length of the string.  They verify the whole string, and return the
 * number of input bytes (<= len) that are valid.  In other words, if the
 * whole string is valid, verifystr returns "len", otherwise it returns the
 * byte offset of the first invalid character.  The verifystr functions must
 * test for and reject zeroes in the input.
 *
 * The verifychar functions can assume that len > 0 and that *s != '\0', but
 * they must test for and reject zeroes in any additional bytes of a
 * multibyte character.  Note that this definition allows the function for a
 * single-byte encoding to be just "return 1".
 *-------------------------------------------------------------------
 */
static int
pg_ascii_verifychar(const unsigned char *s, int len)
{
    return 1;
}
 
static int
pg_ascii_verifystr(const unsigned char *s, int len)
{
    const unsigned char *nullpos = memchr(s, 0, len);
 
    if (nullpos == NULL)
        return len;
    else
        return nullpos - s;
}
 
#define IS_EUC_RANGE_VALID(c)   ((c) >= 0xa1 && (c) <= 0xfe)
 
static int
pg_eucjp_verifychar(const unsigned char *s, int len)
{
    int         l;
    unsigned char c1,
                c2;
 
    c1 = *s++;
 
    switch (c1)
    {
        case SS2:               /* JIS X 0201 */
            l = 2;
            if (l > len)
                return -1;
            c2 = *s++;
            if (c2 < 0xa1 || c2 > 0xdf)
                return -1;
            break;
 
        case SS3:               /* JIS X 0212 */
            l = 3;
            if (l > len)
                return -1;
            c2 = *s++;
            if (!IS_EUC_RANGE_VALID(c2))
                return -1;
            c2 = *s++;
            if (!IS_EUC_RANGE_VALID(c2))
                return -1;
            break;
 
        default:
            if (IS_HIGHBIT_SET(c1)) /* JIS X 0208? */
            {
                l = 2;
                if (l > len)
                    return -1;
                if (!IS_EUC_RANGE_VALID(c1))
                    return -1;
                c2 = *s++;
                if (!IS_EUC_RANGE_VALID(c2))
                    return -1;
            }
            else
                /* must be ASCII */
            {
                l = 1;
            }
            break;
    }
 
    return l;
}
 
static int
pg_eucjp_verifystr(const unsigned char *s, int len)
{
    const unsigned char *start = s;
 
    while (len > 0)
    {
        int         l;
 
        /* fast path for ASCII-subset characters */
        if (!IS_HIGHBIT_SET(*s))
        {
            if (*s == '\0')
                break;
            l = 1;
        }
        else
        {
            l = pg_eucjp_verifychar(s, len);
            if (l == -1)
                break;
        }
        s += l;
        len -= l;
    }
 
    return s - start;
}
 
static int
pg_euckr_verifychar(const unsigned char *s, int len)
{
    int         l;
    unsigned char c1,
                c2;
 
    c1 = *s++;
 
    if (IS_HIGHBIT_SET(c1))
    {
        l = 2;
        if (l > len)
            return -1;
        if (!IS_EUC_RANGE_VALID(c1))
            return -1;
        c2 = *s++;
        if (!IS_EUC_RANGE_VALID(c2))
            return -1;
    }
    else
        /* must be ASCII */
    {
        l = 1;
    }
 
    return l;
}
 
static int
pg_euckr_verifystr(const unsigned char *s, int len)
{
    const unsigned char *start = s;
 
    while (len > 0)
    {
        int         l;
 
        /* fast path for ASCII-subset characters */
        if (!IS_HIGHBIT_SET(*s))
        {
            if (*s == '\0')
                break;
            l = 1;
        }
        else
        {
            l = pg_euckr_verifychar(s, len);
            if (l == -1)
                break;
        }
        s += l;
        len -= l;
    }
 
    return s - start;
}
 
/* EUC-CN byte sequences are exactly same as EUC-KR */
#define pg_euccn_verifychar pg_euckr_verifychar
#define pg_euccn_verifystr  pg_euckr_verifystr
 
static int
pg_euctw_verifychar(const unsigned char *s, int len)
{
    int         l;
    unsigned char c1,
                c2;
 
    c1 = *s++;
 
    switch (c1)
    {
        case SS2:               /* CNS 11643 Plane 1-7 */
            l = 4;
            if (l > len)
                return -1;
            c2 = *s++;
            if (c2 < 0xa1 || c2 > 0xa7)
                return -1;
            c2 = *s++;
            if (!IS_EUC_RANGE_VALID(c2))
                return -1;
            c2 = *s++;
            if (!IS_EUC_RANGE_VALID(c2))
                return -1;
            break;
 
        case SS3:               /* unused */
            return -1;
 
        default:
            if (IS_HIGHBIT_SET(c1)) /* CNS 11643 Plane 1 */
            {
                l = 2;
                if (l > len)
                    return -1;
                /* no further range check on c1? */
                c2 = *s++;
                if (!IS_EUC_RANGE_VALID(c2))
                    return -1;
            }
            else
                /* must be ASCII */
            {
                l = 1;
            }
            break;
    }
    return l;
}
 
static int
pg_euctw_verifystr(const unsigned char *s, int len)
{
    const unsigned char *start = s;
 
    while (len > 0)
    {
        int         l;
 
        /* fast path for ASCII-subset characters */
        if (!IS_HIGHBIT_SET(*s))
        {
            if (*s == '\0')
                break;
            l = 1;
        }
        else
        {
            l = pg_euctw_verifychar(s, len);
            if (l == -1)
                break;
        }
        s += l;
        len -= l;
    }
 
    return s - start;
}
 
static int
pg_johab_verifychar(const unsigned char *s, int len)
{
    int         l,
                mbl;
    unsigned char c;
 
    l = mbl = pg_johab_mblen(s);
 
    if (len < l)
        return -1;
 
    if (!IS_HIGHBIT_SET(*s))
        return mbl;
 
    while (--l > 0)
    {
        c = *++s;
        if (!IS_EUC_RANGE_VALID(c))
            return -1;
    }
    return mbl;
}
 
static int
pg_johab_verifystr(const unsigned char *s, int len)
{
    const unsigned char *start = s;
 
    while (len > 0)
    {
        int         l;
 
        /* fast path for ASCII-subset characters */
        if (!IS_HIGHBIT_SET(*s))
        {
            if (*s == '\0')
                break;
            l = 1;
        }
        else
        {
            l = pg_johab_verifychar(s, len);
            if (l == -1)
                break;
        }
        s += l;
        len -= l;
    }
 
    return s - start;
}
 
static int
pg_mule_verifychar(const unsigned char *s, int len)
{
    int         l,
                mbl;
    unsigned char c;
 
    l = mbl = pg_mule_mblen(s);
 
    if (len < l)
        return -1;
 
    while (--l > 0)
    {
        c = *++s;
        if (!IS_HIGHBIT_SET(c))
            return -1;
    }
    return mbl;
}
 
static int
pg_mule_verifystr(const unsigned char *s, int len)
{
    const unsigned char *start = s;
 
    while (len > 0)
    {
        int         l;
 
        /* fast path for ASCII-subset characters */
        if (!IS_HIGHBIT_SET(*s))
        {
            if (*s == '\0')
                break;
            l = 1;
        }
        else
        {
            l = pg_mule_verifychar(s, len);
            if (l == -1)
                break;
        }
        s += l;
        len -= l;
    }
 
    return s - start;
}
 
static int
pg_latin1_verifychar(const unsigned char *s, int len)
{
    return 1;
}
 
static int
pg_latin1_verifystr(const unsigned char *s, int len)
{
    const unsigned char *nullpos = memchr(s, 0, len);
 
    if (nullpos == NULL)
        return len;
    else
        return nullpos - s;
}
 
static int
pg_sjis_verifychar(const unsigned char *s, int len)
{
    int         l,
                mbl;
    unsigned char c1,
                c2;
 
    l = mbl = pg_sjis_mblen(s);
 
    if (len < l)
        return -1;
 
    if (l == 1)                 /* pg_sjis_mblen already verified it */
        return mbl;
 
    c1 = *s++;
    c2 = *s;
    if (!ISSJISHEAD(c1) || !ISSJISTAIL(c2))
        return -1;
    return mbl;
}
 
static int
pg_sjis_verifystr(const unsigned char *s, int len)
{
    const unsigned char *start = s;
 
    while (len > 0)
    {
        int         l;
 
        /* fast path for ASCII-subset characters */
        if (!IS_HIGHBIT_SET(*s))
        {
            if (*s == '\0')
                break;
            l = 1;
        }
        else
        {
            l = pg_sjis_verifychar(s, len);
            if (l == -1)
                break;
        }
        s += l;
        len -= l;
    }
 
    return s - start;
}
 
static int
pg_big5_verifychar(const unsigned char *s, int len)
{
    int         l,
                mbl;
 
    l = mbl = pg_big5_mblen(s);
 
    if (len < l)
        return -1;
 
    if (l == 2 &&
        s[0] == NONUTF8_INVALID_BYTE0 &&
        s[1] == NONUTF8_INVALID_BYTE1)
        return -1;
 
    while (--l > 0)
    {
        if (*++s == '\0')
            return -1;
    }
 
    return mbl;
}
 
static int
pg_big5_verifystr(const unsigned char *s, int len)
{
    const unsigned char *start = s;
 
    while (len > 0)
    {
        int         l;
 
        /* fast path for ASCII-subset characters */
        if (!IS_HIGHBIT_SET(*s))
        {
            if (*s == '\0')
                break;
            l = 1;
        }
        else
        {
            l = pg_big5_verifychar(s, len);
            if (l == -1)
                break;
        }
        s += l;
        len -= l;
    }
 
    return s - start;
}
 
static int
pg_gbk_verifychar(const unsigned char *s, int len)
{
    int         l,
                mbl;
 
    l = mbl = pg_gbk_mblen(s);
 
    if (len < l)
        return -1;
 
    if (l == 2 &&
        s[0] == NONUTF8_INVALID_BYTE0 &&
        s[1] == NONUTF8_INVALID_BYTE1)
        return -1;
 
    while (--l > 0)
    {
        if (*++s == '\0')
            return -1;
    }
 
    return mbl;
}
 
static int
pg_gbk_verifystr(const unsigned char *s, int len)
{
    const unsigned char *start = s;
 
    while (len > 0)
    {
        int         l;
 
        /* fast path for ASCII-subset characters */
        if (!IS_HIGHBIT_SET(*s))
        {
            if (*s == '\0')
                break;
            l = 1;
        }
        else
        {
            l = pg_gbk_verifychar(s, len);
            if (l == -1)
                break;
        }
        s += l;
        len -= l;
    }
 
    return s - start;
}
 
static int
pg_uhc_verifychar(const unsigned char *s, int len)
{
    int         l,
                mbl;
 
    l = mbl = pg_uhc_mblen(s);
 
    if (len < l)
        return -1;
 
    if (l == 2 &&
        s[0] == NONUTF8_INVALID_BYTE0 &&
        s[1] == NONUTF8_INVALID_BYTE1)
        return -1;
 
    while (--l > 0)
    {
        if (*++s == '\0')
            return -1;
    }
 
    return mbl;
}
 
static int
pg_uhc_verifystr(const unsigned char *s, int len)
{
    const unsigned char *start = s;
 
    while (len > 0)
    {
        int         l;
 
        /* fast path for ASCII-subset characters */
        if (!IS_HIGHBIT_SET(*s))
        {
            if (*s == '\0')
                break;
            l = 1;
        }
        else
        {
            l = pg_uhc_verifychar(s, len);
            if (l == -1)
                break;
        }
        s += l;
        len -= l;
    }
 
    return s - start;
}
 
static int
pg_gb18030_verifychar(const unsigned char *s, int len)
{
    int         l;
 
    if (!IS_HIGHBIT_SET(*s))
        l = 1;                  /* ASCII */
    else if (len >= 4 && *(s + 1) >= 0x30 && *(s + 1) <= 0x39)
    {
        /* Should be 4-byte, validate remaining bytes */
        if (*s >= 0x81 && *s <= 0xfe &&
            *(s + 2) >= 0x81 && *(s + 2) <= 0xfe &&
            *(s + 3) >= 0x30 && *(s + 3) <= 0x39)
            l = 4;
        else
            l = -1;
    }
    else if (len >= 2 && *s >= 0x81 && *s <= 0xfe)
    {
        /* Should be 2-byte, validate */
        if ((*(s + 1) >= 0x40 && *(s + 1) <= 0x7e) ||
            (*(s + 1) >= 0x80 && *(s + 1) <= 0xfe))
            l = 2;
        else
            l = -1;
    }
    else
        l = -1;
    return l;
}
 
static int
pg_gb18030_verifystr(const unsigned char *s, int len)
{
    const unsigned char *start = s;
 
    while (len > 0)
    {
        int         l;
 
        /* fast path for ASCII-subset characters */
        if (!IS_HIGHBIT_SET(*s))
        {
            if (*s == '\0')
                break;
            l = 1;
        }
        else
        {
            l = pg_gb18030_verifychar(s, len);
            if (l == -1)
                break;
        }
        s += l;
        len -= l;
    }
 
    return s - start;
}
 
static int
pg_utf8_verifychar(const unsigned char *s, int len)
{
    int         l;
 
    if ((*s & 0x80) == 0)
    {
        if (*s == '\0')
            return -1;
        return 1;
    }
    else if ((*s & 0xe0) == 0xc0)
        l = 2;
    else if ((*s & 0xf0) == 0xe0)
        l = 3;
    else if ((*s & 0xf8) == 0xf0)
        l = 4;
    else
        l = 1;
 
    if (l > len)
        return -1;
 
    if (!pg_utf8_islegal(s, l))
        return -1;
 
    return l;
}
 
/*
 * The fast path of the UTF-8 verifier uses a deterministic finite automaton
 * (DFA) for multibyte characters. In a traditional table-driven DFA, the
 * input byte and current state are used to compute an index into an array of
 * state transitions. Since the address of the next transition is dependent
 * on this computation, there is latency in executing the load instruction,
 * and the CPU is not kept busy.
 *
 * Instead, we use a "shift-based" DFA as described by Per Vognsen:
 *
 * https://gist.github.com/pervognsen/218ea17743e1442e59bb60d29b1aa725
 *
 * In a shift-based DFA, the input byte is an index into array of integers
 * whose bit pattern encodes the state transitions. To compute the next
 * state, we simply right-shift the integer by the current state and apply a
 * mask. In this scheme, the address of the transition only depends on the
 * input byte, so there is better pipelining.
 *
 * The naming convention for states and transitions was adopted from a UTF-8
 * to UTF-16/32 transcoder, whose table is reproduced below:
 *
 * https://github.com/BobSteagall/utf_utils/blob/6b7a465265de2f5fa6133d653df0c9bdd73bbcf8/src/utf_utils.cpp
 *
 * ILL  ASC  CR1  CR2  CR3  L2A  L3A  L3B  L3C  L4A  L4B  L4C CLASS / STATE
 * ==========================================================================
 * err, END, err, err, err, CS1, P3A, CS2, P3B, P4A, CS3, P4B,      | BGN/END
 * err, err, err, err, err, err, err, err, err, err, err, err,      | ERR
 *                                                                  |
 * err, err, END, END, END, err, err, err, err, err, err, err,      | CS1
 * err, err, CS1, CS1, CS1, err, err, err, err, err, err, err,      | CS2
 * err, err, CS2, CS2, CS2, err, err, err, err, err, err, err,      | CS3
 *                                                                  |
 * err, err, err, err, CS1, err, err, err, err, err, err, err,      | P3A
 * err, err, CS1, CS1, err, err, err, err, err, err, err, err,      | P3B
 *                                                                  |
 * err, err, err, CS2, CS2, err, err, err, err, err, err, err,      | P4A
 * err, err, CS2, err, err, err, err, err, err, err, err, err,      | P4B
 *
 * In the most straightforward implementation, a shift-based DFA for UTF-8
 * requires 64-bit integers to encode the transitions, but with an SMT solver
 * it's possible to find state numbers such that the transitions fit within
 * 32-bit integers, as Dougall Johnson demonstrated:
 *
 * https://gist.github.com/dougallj/166e326de6ad4cf2c94be97a204c025f
 *
 * This packed representation is the reason for the seemingly odd choice of
 * state values below.
 */
 
/* Error */
#define ERR  0
/* Begin */
#define BGN 11
/* Continuation states, expect 1/2/3 continuation bytes */
#define CS1 16
#define CS2  1
#define CS3  5
/* Partial states, where the first continuation byte has a restricted range */
#define P3A  6                  /* Lead was E0, check for 3-byte overlong */
#define P3B 20                  /* Lead was ED, check for surrogate */
#define P4A 25                  /* Lead was F0, check for 4-byte overlong */
#define P4B 30                  /* Lead was F4, check for too-large */
/* Begin and End are the same state */
#define END BGN
 
/* the encoded state transitions for the lookup table */
 
/* ASCII */
#define ASC (END << BGN)
/* 2-byte lead */
#define L2A (CS1 << BGN)
/* 3-byte lead */
#define L3A (P3A << BGN)
#define L3B (CS2 << BGN)
#define L3C (P3B << BGN)
/* 4-byte lead */
#define L4A (P4A << BGN)
#define L4B (CS3 << BGN)
#define L4C (P4B << BGN)
/* continuation byte */
#define CR1 (END << CS1) | (CS1 << CS2) | (CS2 << CS3) | (CS1 << P3B) | (CS2 << P4B)
#define CR2 (END << CS1) | (CS1 << CS2) | (CS2 << CS3) | (CS1 << P3B) | (CS2 << P4A)
#define CR3 (END << CS1) | (CS1 << CS2) | (CS2 << CS3) | (CS1 << P3A) | (CS2 << P4A)
/* invalid byte */
#define ILL ERR
 
static const uint32 Utf8Transition[256] =
{
    /* ASCII */
 
    ILL, ASC, ASC, ASC, ASC, ASC, ASC, ASC,
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,
 
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,
 
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,
 
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,
 
    /* continuation bytes */
 
    /* 80..8F */
    CR1, CR1, CR1, CR1, CR1, CR1, CR1, CR1,
    CR1, CR1, CR1, CR1, CR1, CR1, CR1, CR1,
 
    /* 90..9F */
    CR2, CR2, CR2, CR2, CR2, CR2, CR2, CR2,
    CR2, CR2, CR2, CR2, CR2, CR2, CR2, CR2,
 
    /* A0..BF */
    CR3, CR3, CR3, CR3, CR3, CR3, CR3, CR3,
    CR3, CR3, CR3, CR3, CR3, CR3, CR3, CR3,
    CR3, CR3, CR3, CR3, CR3, CR3, CR3, CR3,
    CR3, CR3, CR3, CR3, CR3, CR3, CR3, CR3,
 
    /* leading bytes */
 
    /* C0..DF */
    ILL, ILL, L2A, L2A, L2A, L2A, L2A, L2A,
    L2A, L2A, L2A, L2A, L2A, L2A, L2A, L2A,
    L2A, L2A, L2A, L2A, L2A, L2A, L2A, L2A,
    L2A, L2A, L2A, L2A, L2A, L2A, L2A, L2A,
 
    /* E0..EF */
    L3A, L3B, L3B, L3B, L3B, L3B, L3B, L3B,
    L3B, L3B, L3B, L3B, L3B, L3C, L3B, L3B,
 
    /* F0..FF */
    L4A, L4B, L4B, L4B, L4C, ILL, ILL, ILL,
    ILL, ILL, ILL, ILL, ILL, ILL, ILL, ILL
};
 
static void
utf8_advance(const unsigned char *s, uint32 *state, int len)
{
    /* Note: We deliberately don't check the state's value here. */
    while (len > 0)
    {
        /*
         * It's important that the mask value is 31: In most instruction sets,
         * a shift by a 32-bit operand is understood to be a shift by its mod
         * 32, so the compiler should elide the mask operation.
         */
        *state = Utf8Transition[*s++] >> (*state & 31);
        len--;
    }
 
    *state &= 31;
}
 
static int
pg_utf8_verifystr(const unsigned char *s, int len)
{
    const unsigned char *start = s;
    const int   orig_len = len;
    uint32      state = BGN;
 
/*
 * With a stride of two vector widths, gcc will unroll the loop. Even if
 * the compiler can unroll a longer loop, it's not worth it because we
 * must fall back to the byte-wise algorithm if we find any non-ASCII.
 */
#define STRIDE_LENGTH (2 * sizeof(Vector8))
 
    if (len >= STRIDE_LENGTH)
    {
        while (len >= STRIDE_LENGTH)
        {
            /*
             * If the chunk is all ASCII, we can skip the full UTF-8 check,
             * but we must first check for a non-END state, which means the
             * previous chunk ended in the middle of a multibyte sequence.
             */
            if (state != END || !is_valid_ascii(s, STRIDE_LENGTH))
                utf8_advance(s, &state, STRIDE_LENGTH);
 
            s += STRIDE_LENGTH;
            len -= STRIDE_LENGTH;
        }
 
        /* The error state persists, so we only need to check for it here. */
        if (state == ERR)
        {
            /*
             * Start over from the beginning with the slow path so we can
             * count the valid bytes.
             */
            len = orig_len;
            s = start;
        }
        else if (state != END)
        {
            /*
             * The fast path exited in the middle of a multibyte sequence.
             * Walk backwards to find the leading byte so that the slow path
             * can resume checking from there. We must always backtrack at
             * least one byte, since the current byte could be e.g. an ASCII
             * byte after a 2-byte lead, which is invalid.
             */
            do
            {
                Assert(s > start);
                s--;
                len++;
                Assert(IS_HIGHBIT_SET(*s));
            } while (pg_utf_mblen(s) <= 1);
        }
    }
 
    /* check remaining bytes */
    while (len > 0)
    {
        int         l;
 
        /* fast path for ASCII-subset characters */
        if (!IS_HIGHBIT_SET(*s))
        {
            if (*s == '\0')
                break;
            l = 1;
        }
        else
        {
            l = pg_utf8_verifychar(s, len);
            if (l == -1)
                break;
        }
        s += l;
        len -= l;
    }
 
    return s - start;
}
 
/*
 * Check for validity of a single UTF-8 encoded character
 *
 * This directly implements the rules in RFC3629.  The bizarre-looking
 * restrictions on the second byte are meant to ensure that there isn't
 * more than one encoding of a given Unicode character point; that is,
 * you may not use a longer-than-necessary byte sequence with high order
 * zero bits to represent a character that would fit in fewer bytes.
 * To do otherwise is to create security hazards (eg, create an apparent
 * non-ASCII character that decodes to plain ASCII).
 *
 * length is assumed to have been obtained by pg_utf_mblen(), and the
 * caller must have checked that that many bytes are present in the buffer.
 */
bool
pg_utf8_islegal(const unsigned char *source, int length)
{
    unsigned char a;
 
    switch (length)
    {
        default:
            /* reject lengths 5 and 6 for now */
            return false;
        case 4:
            a = source[3];
            if (a < 0x80 || a > 0xBF)
                return false;
            /* FALL THRU */
        case 3:
            a = source[2];
            if (a < 0x80 || a > 0xBF)
                return false;
            /* FALL THRU */
        case 2:
            a = source[1];
            switch (*source)
            {
                case 0xE0:
                    if (a < 0xA0 || a > 0xBF)
                        return false;
                    break;
                case 0xED:
                    if (a < 0x80 || a > 0x9F)
                        return false;
                    break;
                case 0xF0:
                    if (a < 0x90 || a > 0xBF)
                        return false;
                    break;
                case 0xF4:
                    if (a < 0x80 || a > 0x8F)
                        return false;
                    break;
                default:
                    if (a < 0x80 || a > 0xBF)
                        return false;
                    break;
            }
            /* FALL THRU */
        case 1:
            a = *source;
            if (a >= 0x80 && a < 0xC2)
                return false;
            if (a > 0xF4)
                return false;
            break;
    }
    return true;
}
 
 
/*
 * Fills the provided buffer with two bytes such that:
 *   pg_encoding_mblen(dst) == 2 && pg_encoding_verifymbstr(dst) == 0
 */
void
pg_encoding_set_invalid(int encoding, char *dst)
{
    Assert(pg_encoding_max_length(encoding) > 1);
 
    dst[0] = (encoding == PG_UTF8 ? 0xc0 : NONUTF8_INVALID_BYTE0);
    dst[1] = NONUTF8_INVALID_BYTE1;
}
 
/*
 *-------------------------------------------------------------------
 * encoding info table
 *-------------------------------------------------------------------
 */
const pg_wchar_tbl pg_wchar_table[] = {
    [PG_SQL_ASCII] = {pg_ascii2wchar_with_len, pg_wchar2single_with_len, pg_ascii_mblen, pg_ascii_dsplen, pg_ascii_verifychar, pg_ascii_verifystr, 1},
    [PG_EUC_JP] = {pg_eucjp2wchar_with_len, pg_wchar2euc_with_len, pg_eucjp_mblen, pg_eucjp_dsplen, pg_eucjp_verifychar, pg_eucjp_verifystr, 3},
    [PG_EUC_CN] = {pg_euccn2wchar_with_len, pg_wchar2euc_with_len, pg_euccn_mblen, pg_euccn_dsplen, pg_euccn_verifychar, pg_euccn_verifystr, 2},
    [PG_EUC_KR] = {pg_euckr2wchar_with_len, pg_wchar2euc_with_len, pg_euckr_mblen, pg_euckr_dsplen, pg_euckr_verifychar, pg_euckr_verifystr, 3},
    [PG_EUC_TW] = {pg_euctw2wchar_with_len, pg_wchar2euc_with_len, pg_euctw_mblen, pg_euctw_dsplen, pg_euctw_verifychar, pg_euctw_verifystr, 4},
    [PG_EUC_JIS_2004] = {pg_eucjp2wchar_with_len, pg_wchar2euc_with_len, pg_eucjp_mblen, pg_eucjp_dsplen, pg_eucjp_verifychar, pg_eucjp_verifystr, 3},
    [PG_UTF8] = {pg_utf2wchar_with_len, pg_wchar2utf_with_len, pg_utf_mblen, pg_utf_dsplen, pg_utf8_verifychar, pg_utf8_verifystr, 4},
    [PG_MULE_INTERNAL] = {pg_mule2wchar_with_len, pg_wchar2mule_with_len, pg_mule_mblen, pg_mule_dsplen, pg_mule_verifychar, pg_mule_verifystr, 4},
    [PG_LATIN1] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_LATIN2] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_LATIN3] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_LATIN4] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_LATIN5] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_LATIN6] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_LATIN7] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_LATIN8] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_LATIN9] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_LATIN10] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_WIN1256] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_WIN1258] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_WIN866] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_WIN874] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_KOI8R] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_WIN1251] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_WIN1252] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_ISO_8859_5] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_ISO_8859_6] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_ISO_8859_7] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_ISO_8859_8] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_WIN1250] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_WIN1253] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_WIN1254] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_WIN1255] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_WIN1257] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_KOI8U] = {pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifychar, pg_latin1_verifystr, 1},
    [PG_SJIS] = {0, 0, pg_sjis_mblen, pg_sjis_dsplen, pg_sjis_verifychar, pg_sjis_verifystr, 2},
    [PG_BIG5] = {0, 0, pg_big5_mblen, pg_big5_dsplen, pg_big5_verifychar, pg_big5_verifystr, 2},
    [PG_GBK] = {0, 0, pg_gbk_mblen, pg_gbk_dsplen, pg_gbk_verifychar, pg_gbk_verifystr, 2},
    [PG_UHC] = {0, 0, pg_uhc_mblen, pg_uhc_dsplen, pg_uhc_verifychar, pg_uhc_verifystr, 2},
    [PG_GB18030] = {0, 0, pg_gb18030_mblen, pg_gb18030_dsplen, pg_gb18030_verifychar, pg_gb18030_verifystr, 4},
    [PG_JOHAB] = {0, 0, pg_johab_mblen, pg_johab_dsplen, pg_johab_verifychar, pg_johab_verifystr, 3},
    [PG_SHIFT_JIS_2004] = {0, 0, pg_sjis_mblen, pg_sjis_dsplen, pg_sjis_verifychar, pg_sjis_verifystr, 2},
};
 
/*
 * Returns the byte length of a multibyte character.
 *
 * Choose "mblen" functions based on the input string characteristics.
 * pg_encoding_mblen() can be used when ANY of these conditions are met:
 *
 * - The input string is zero-terminated
 *
 * - The input string is known to be valid in the encoding (e.g., string
 *   converted from database encoding)
 *
 * - The encoding is not GB18030 (e.g., when only database encodings are
 *   passed to 'encoding' parameter)
 *
 * encoding==GB18030 requires examining up to two bytes to determine character
 * length.  Therefore, callers satisfying none of those conditions must use
 * pg_encoding_mblen_or_incomplete() instead, as access to mbstr[1] cannot be
 * guaranteed to be within allocation bounds.
 *
 * When dealing with text that is not certainly valid in the specified
 * encoding, the result may exceed the actual remaining string length.
 * Callers that are not prepared to deal with that should use Min(remaining,
 * pg_encoding_mblen_or_incomplete()).  For zero-terminated strings, that and
 * pg_encoding_mblen_bounded() are interchangeable.
 */
int
pg_encoding_mblen(int encoding, const char *mbstr)
{
    return (PG_VALID_ENCODING(encoding) ?
            pg_wchar_table[encoding].mblen((const unsigned char *) mbstr) :
            pg_wchar_table[PG_SQL_ASCII].mblen((const unsigned char *) mbstr));
}
 
/*
 * Returns the byte length of a multibyte character (possibly not
 * zero-terminated), or INT_MAX if too few bytes remain to determine a length.
 */
int
pg_encoding_mblen_or_incomplete(int encoding, const char *mbstr,
                                size_t remaining)
{
    /*
     * Define zero remaining as too few, even for single-byte encodings.
     * pg_gb18030_mblen() reads one or two bytes; single-byte encodings read
     * zero; others read one.
     */
    if (remaining < 1 ||
        (encoding == PG_GB18030 && IS_HIGHBIT_SET(*mbstr) && remaining < 2))
        return INT_MAX;
    return pg_encoding_mblen(encoding, mbstr);
}
 
/*
 * Returns the byte length of a multibyte character; but not more than the
 * distance to the terminating zero byte.  For input that might lack a
 * terminating zero, use Min(remaining, pg_encoding_mblen_or_incomplete()).
 */
int
pg_encoding_mblen_bounded(int encoding, const char *mbstr)
{
    return strnlen(mbstr, pg_encoding_mblen(encoding, mbstr));
}
 
/*
 * Returns the display length of a multibyte character.
 */
int
pg_encoding_dsplen(int encoding, const char *mbstr)
{
    return (PG_VALID_ENCODING(encoding) ?
            pg_wchar_table[encoding].dsplen((const unsigned char *) mbstr) :
            pg_wchar_table[PG_SQL_ASCII].dsplen((const unsigned char *) mbstr));
}
 
/*
 * Verify the first multibyte character of the given string.
 * Return its byte length if good, -1 if bad.  (See comments above for
 * full details of the mbverifychar API.)
 */
int
pg_encoding_verifymbchar(int encoding, const char *mbstr, int len)
{
    return (PG_VALID_ENCODING(encoding) ?
            pg_wchar_table[encoding].mbverifychar((const unsigned char *) mbstr, len) :
            pg_wchar_table[PG_SQL_ASCII].mbverifychar((const unsigned char *) mbstr, len));
}
 
/*
 * Verify that a string is valid for the given encoding.
 * Returns the number of input bytes (<= len) that form a valid string.
 * (See comments above for full details of the mbverifystr API.)
 */
int
pg_encoding_verifymbstr(int encoding, const char *mbstr, int len)
{
    return (PG_VALID_ENCODING(encoding) ?
            pg_wchar_table[encoding].mbverifystr((const unsigned char *) mbstr, len) :
            pg_wchar_table[PG_SQL_ASCII].mbverifystr((const unsigned char *) mbstr, len));
}
 
/*
 * fetch maximum length of a given encoding
 */
int
pg_encoding_max_length(int encoding)
{
    Assert(PG_VALID_ENCODING(encoding));
 
    /*
     * Check for the encoding despite the assert, due to some mingw versions
     * otherwise issuing bogus warnings.
     */
    return PG_VALID_ENCODING(encoding) ?
        pg_wchar_table[encoding].maxmblen :
        pg_wchar_table[PG_SQL_ASCII].maxmblen;
}