postgres/src/common/wchar.c

/*-------------------------------------------------------------------------
 *
 * wchar.c
 *	  Functions for working with multibyte characters in various encodings.
 *
 * Portions Copyright (c) 1998-2020, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *	  src/common/wchar.c
 *
 *-------------------------------------------------------------------------
 */
#include "c.h"

#include <limits.h>

#include "mb/pg_wchar.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() and verifier() 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;
}


/*
 * Map a Unicode code point to UTF-8.  utf8string must have 4 bytes of
 * space allocated.
 */
unsigned char *
unicode_to_utf8(pg_wchar c, unsigned char *utf8string)
{
	if (c <= 0x7F)
	{
		utf8string[0] = c;
	}
	else if (c <= 0x7FF)
	{
		utf8string[0] = 0xC0 | ((c >> 6) & 0x1F);
		utf8string[1] = 0x80 | (c & 0x3F);
	}
	else if (c <= 0xFFFF)
	{
		utf8string[0] = 0xE0 | ((c >> 12) & 0x0F);
		utf8string[1] = 0x80 | ((c >> 6) & 0x3F);
		utf8string[2] = 0x80 | (c & 0x3F);
	}
	else
	{
		utf8string[0] = 0xF0 | ((c >> 18) & 0x07);
		utf8string[1] = 0x80 | ((c >> 12) & 0x3F);
		utf8string[2] = 0x80 | ((c >> 6) & 0x3F);
		utf8string[3] = 0x80 | (c & 0x3F);
	}

	return utf8string;
}

/*
 * 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 short first;
	unsigned short 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 or Me in the Unicode database) have a
 *		column width of 0.
 *
 *	  - Other format characters (general category code Cf in the Unicode
 *		database) and ZERO WIDTH SPACE (U+200B) have a column width of 0.
 *
 *	  - Hangul Jamo medial vowels and final consonants (U+1160-U+11FF)
 *		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_combining_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 */
	if (mbbisearch(ucs, combining,
				   sizeof(combining) / sizeof(struct mbinterval) - 1))
		return 0;

	/*
	 * if we arrive here, ucs is not a combining or C0/C1 control character
	 */

	return 1 +
		(ucs >= 0x1100 &&
		 (ucs <= 0x115f ||		/* Hangul Jamo init. consonants */
		  (ucs >= 0x2e80 && ucs <= 0xa4cf && (ucs & ~0x0011) != 0x300a &&
		   ucs != 0x303f) ||	/* CJK ... Yi */
		  (ucs >= 0xac00 && ucs <= 0xd7a3) ||	/* Hangul Syllables */
		  (ucs >= 0xf900 && ucs <= 0xfaff) ||	/* CJK Compatibility
												 * Ideographs */
		  (ucs >= 0xfe30 && ucs <= 0xfe6f) ||	/* CJK Compatibility Forms */
		  (ucs >= 0xff00 && ucs <= 0xff5f) ||	/* Fullwidth Forms */
		  (ucs >= 0xffe0 && ucs <= 0xffe6) ||
		  (ucs >= 0x20000 && ucs <= 0x2ffff)));
}

/*
 * Convert a UTF-8 character to a Unicode code point.
 * This is a one-character version of pg_utf2wchar_with_len.
 *
 * No error checks here, c must point to a long-enough string.
 */
pg_wchar
utf8_to_unicode(const unsigned char *c)
{
	if ((*c & 0x80) == 0)
		return (pg_wchar) c[0];
	else if ((*c & 0xe0) == 0xc0)
		return (pg_wchar) (((c[0] & 0x1f) << 6) |
						   (c[1] & 0x3f));
	else if ((*c & 0xf0) == 0xe0)
		return (pg_wchar) (((c[0] & 0x0f) << 12) |
						   ((c[1] & 0x3f) << 6) |
						   (c[2] & 0x3f));
	else if ((*c & 0xf8) == 0xf0)
		return (pg_wchar) (((c[0] & 0x07) << 18) |
						   ((c[1] & 0x3f) << 12) |
						   ((c[2] & 0x3f) << 6) |
						   (c[3] & 0x3f));
	else
		/* that is an invalid code on purpose */
		return 0xffffffff;
}

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
 *
 * These 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 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_verifier(const unsigned char *s, int len)
{
	return 1;
}

#define IS_EUC_RANGE_VALID(c)	((c) >= 0xa1 && (c) <= 0xfe)

static int
pg_eucjp_verifier(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_euckr_verifier(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;
}

/* EUC-CN byte sequences are exactly same as EUC-KR */
#define pg_euccn_verifier	pg_euckr_verifier

static int
pg_euctw_verifier(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_johab_verifier(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_mule_verifier(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_latin1_verifier(const unsigned char *s, int len)
{
	return 1;
}

static int
pg_sjis_verifier(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_big5_verifier(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_gbk_verifier(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_uhc_verifier(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_gb18030_verifier(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_utf8_verifier(const unsigned char *s, int len)
{
	int			l = pg_utf_mblen(s);

	if (len < l)
		return -1;

	if (!pg_utf8_islegal(s, l))
		return -1;

	return l;
}

/*
 * 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
 * XXX must be sorted by the same order as enum pg_enc (in mb/pg_wchar.h)
 *-------------------------------------------------------------------
 */
const pg_wchar_tbl pg_wchar_table[] = {
	{pg_ascii2wchar_with_len, pg_wchar2single_with_len, pg_ascii_mblen, pg_ascii_dsplen, pg_ascii_verifier, 1}, /* PG_SQL_ASCII */
	{pg_eucjp2wchar_with_len, pg_wchar2euc_with_len, pg_eucjp_mblen, pg_eucjp_dsplen, pg_eucjp_verifier, 3},	/* PG_EUC_JP */
	{pg_euccn2wchar_with_len, pg_wchar2euc_with_len, pg_euccn_mblen, pg_euccn_dsplen, pg_euccn_verifier, 2},	/* PG_EUC_CN */
	{pg_euckr2wchar_with_len, pg_wchar2euc_with_len, pg_euckr_mblen, pg_euckr_dsplen, pg_euckr_verifier, 3},	/* PG_EUC_KR */
	{pg_euctw2wchar_with_len, pg_wchar2euc_with_len, pg_euctw_mblen, pg_euctw_dsplen, pg_euctw_verifier, 4},	/* PG_EUC_TW */
	{pg_eucjp2wchar_with_len, pg_wchar2euc_with_len, pg_eucjp_mblen, pg_eucjp_dsplen, pg_eucjp_verifier, 3},	/* PG_EUC_JIS_2004 */
	{pg_utf2wchar_with_len, pg_wchar2utf_with_len, pg_utf_mblen, pg_utf_dsplen, pg_utf8_verifier, 4},	/* PG_UTF8 */
	{pg_mule2wchar_with_len, pg_wchar2mule_with_len, pg_mule_mblen, pg_mule_dsplen, pg_mule_verifier, 4},	/* PG_MULE_INTERNAL */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_LATIN1 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_LATIN2 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_LATIN3 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_LATIN4 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_LATIN5 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_LATIN6 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_LATIN7 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_LATIN8 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_LATIN9 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_LATIN10 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_WIN1256 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_WIN1258 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_WIN866 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_WIN874 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_KOI8R */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_WIN1251 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_WIN1252 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* ISO-8859-5 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* ISO-8859-6 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* ISO-8859-7 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* ISO-8859-8 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_WIN1250 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_WIN1253 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_WIN1254 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_WIN1255 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_WIN1257 */
	{pg_latin12wchar_with_len, pg_wchar2single_with_len, pg_latin1_mblen, pg_latin1_dsplen, pg_latin1_verifier, 1}, /* PG_KOI8U */
	{0, 0, pg_sjis_mblen, pg_sjis_dsplen, pg_sjis_verifier, 2}, /* PG_SJIS */
	{0, 0, pg_big5_mblen, pg_big5_dsplen, pg_big5_verifier, 2}, /* PG_BIG5 */
	{0, 0, pg_gbk_mblen, pg_gbk_dsplen, pg_gbk_verifier, 2},	/* PG_GBK */
	{0, 0, pg_uhc_mblen, pg_uhc_dsplen, pg_uhc_verifier, 2},	/* PG_UHC */
	{0, 0, pg_gb18030_mblen, pg_gb18030_dsplen, pg_gb18030_verifier, 4},	/* PG_GB18030 */
	{0, 0, pg_johab_mblen, pg_johab_dsplen, pg_johab_verifier, 3},	/* PG_JOHAB */
	{0, 0, pg_sjis_mblen, pg_sjis_dsplen, pg_sjis_verifier, 2}	/* PG_SHIFT_JIS_2004 */
};

/*
 * 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 mbverify API.)
 */
int
pg_encoding_verifymb(int encoding, const char *mbstr, int len)
{
	return (PG_VALID_ENCODING(encoding) ?
			pg_wchar_table[encoding].mbverify((const unsigned char *) mbstr, len) :
			pg_wchar_table[PG_SQL_ASCII].mbverify((const unsigned char *) mbstr, len));
}

/* v14+ function name, for easier backpatching */
int
pg_encoding_verifymbchar(int encoding, const char *mbstr, int len)
{
	int ok_bytes = pg_encoding_verifymb(encoding, mbstr, len);

	if (ok_bytes == 0)
		return -1;
	return ok_bytes;
}

/* replace v14+ function, adapted from pg_verify_mbstr_len */
int
pg_encoding_verifymbstr(int encoding, const char *mbstr, int len)
{
	mbverifier	mbverify;
	int			ok_bytes;

	Assert(PG_VALID_ENCODING(encoding));

	/*
	 * In single-byte encodings, we need only reject nulls (\0).
	 */
	if (pg_encoding_max_length(encoding) <= 1)
	{
		const char *nullpos = memchr(mbstr, 0, len);

		if (nullpos == NULL)
			return len;
		return nullpos - mbstr;
	}

	/* fetch function pointer just once */
	mbverify = pg_wchar_table[encoding].mbverify;

	ok_bytes = 0;

	while (len > 0)
	{
		int			l;

		/* fast path for ASCII-subset characters */
		if (!IS_HIGHBIT_SET(*mbstr))
		{
			if (*mbstr != '\0')
			{
				ok_bytes++;
				mbstr++;
				len--;
				continue;
			}
			return ok_bytes;
		}

		l = (*mbverify) ((const unsigned char *) mbstr, len);

		if (l < 0)
			return ok_bytes;

		mbstr += l;
		len -= l;
		ok_bytes += l;
	}
	return ok_bytes;
}

/*
 * 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;
}