Add wchar -> mb conversion routines.

This is infrastructure for Alexander Korotkov's work on indexing regular
expression searches.

Alexander Korotkov, with a bit of further hackery on the MULE conversion
by me

src/backend/utils/mb/mbutils.c

@@ -710,6 +710,28 @@ pg_encoding_mb2wchar_with_len(int encoding,
 	return (*pg_wchar_table[encoding].mb2wchar_with_len) ((const unsigned char *) from, to, len);
 }
 
+/* convert a wchar string to a multibyte */
+int
+pg_wchar2mb(const pg_wchar *from, char *to)
+{
+	return (*pg_wchar_table[DatabaseEncoding->encoding].wchar2mb_with_len) (from, (unsigned char *)to, pg_wchar_strlen(from));
+}
+
+/* convert a wchar string to a multibyte with a limited length */
+int
+pg_wchar2mb_with_len(const pg_wchar *from, char *to, int len)
+{
+	return (*pg_wchar_table[DatabaseEncoding->encoding].wchar2mb_with_len) (from, (unsigned char *)to, len);
+}
+
+/* same, with any encoding */
+int
+pg_encoding_wchar2mb_with_len(int encoding,
+							  const pg_wchar *from, char *to, int len)
+{
+	return (*pg_wchar_table[encoding].wchar2mb_with_len) (from, (unsigned char *)to, len);
+}
+
 /* returns the byte length of a multibyte character */
 int
 pg_mblen(const char *mbstr)

src/include/mb/pg_wchar.h

@@ -140,6 +140,10 @@ typedef unsigned int pg_wchar;
 #define LCPRV1_A		0x9a
 #define LCPRV1_B		0x9b
 #define IS_LCPRV1(c)	((unsigned char)(c) == LCPRV1_A || (unsigned char)(c) == LCPRV1_B)
+#define IS_LCPRV1_A_RANGE(c)	\
+	((unsigned char)(c) >= 0xa0 && (unsigned char)(c) <= 0xdf)
+#define IS_LCPRV1_B_RANGE(c)	\
+	((unsigned char)(c) >= 0xe0 && (unsigned char)(c) <= 0xef)
 
 /*
  * Postgres-specific prefix bytes for "private" multibyte encodings
@@ -148,6 +152,10 @@ typedef unsigned int pg_wchar;
 #define LCPRV2_A		0x9c
 #define LCPRV2_B		0x9d
 #define IS_LCPRV2(c)	((unsigned char)(c) == LCPRV2_A || (unsigned char)(c) == LCPRV2_B)
+#define IS_LCPRV2_A_RANGE(c)	\
+	((unsigned char)(c) >= 0xf0 && (unsigned char)(c) <= 0xf4)
+#define IS_LCPRV2_B_RANGE(c)	\
+	((unsigned char)(c) >= 0xf5 && (unsigned char)(c) <= 0xfe)
 
 /*
  * Charset IDs for private single byte encodings (0xa0-0xef)
@@ -324,7 +332,11 @@ extern pg_enc2gettext pg_enc2gettext_tbl[];
  * pg_wchar stuff
  */
 typedef int (*mb2wchar_with_len_converter) (const unsigned char *from,
-														pg_wchar *to,
+													pg_wchar *to,
+													int len);
+
+typedef int (*wchar2mb_with_len_converter) (const pg_wchar *from,
+														unsigned char *to,
 														int len);
 
 typedef int (*mblen_converter) (const unsigned char *mbstr);
@@ -337,8 +349,10 @@ typedef int (*mbverifier) (const unsigned char *mbstr, int len);
 
 typedef struct
 {
-	mb2wchar_with_len_converter mb2wchar_with_len;		/* convert a multibyte
-														 * string to a wchar */
+	mb2wchar_with_len_converter mb2wchar_with_len;	/* convert a multibyte
+													 * string to a wchar */
+	wchar2mb_with_len_converter wchar2mb_with_len;	/* convert a wchar
+													 * string to a multibyte */
 	mblen_converter mblen;		/* get byte length of a char */
 	mbdisplaylen_converter dsplen;		/* get display width of a char */
 	mbverifier	mbverify;		/* verify multibyte sequence */
@@ -419,6 +433,10 @@ extern int	pg_mb2wchar(const char *from, pg_wchar *to);
 extern int	pg_mb2wchar_with_len(const char *from, pg_wchar *to, int len);
 extern int pg_encoding_mb2wchar_with_len(int encoding,
 							  const char *from, pg_wchar *to, int len);
+extern int	pg_wchar2mb(const pg_wchar *from, char *to);
+extern int	pg_wchar2mb_with_len(const pg_wchar *from, char *to, int len);
+extern int pg_encoding_wchar2mb_with_len(int encoding,
+							  const pg_wchar *from, char *to, int len);
 extern int	pg_char_and_wchar_strcmp(const char *s1, const pg_wchar *s2);
 extern int	pg_wchar_strncmp(const pg_wchar *s1, const pg_wchar *s2, size_t n);
 extern int	pg_char_and_wchar_strncmp(const char *s1, const pg_wchar *s2, size_t n);