Support RN (roman-numeral format) in to_number().

We've long had roman-numeral output support in to_char(),
but lacked the reverse conversion.  Here it is.

Author: Hunaid Sohail <hunaidpgml@gmail.com>
Reviewed-by: Maciek Sakrejda <m.sakrejda@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Tomas Vondra <tomas@vondra.me>
Discussion: https://postgr.es/m/CAMWA6ybh4M1VQqpmnu2tfSwO+3gAPeA8YKnMHVADeB=XDEvT_A@mail.gmail.com

doc/src/sgml/func.sgml

@@ -8669,8 +8669,8 @@ SELECT regexp_match('abc01234xyz', '(?:(.*?)(\d+)(.*)){1,1}');
         <entry>plus/minus sign in specified position</entry>
        </row>
        <row>
-        <entry><literal>RN</literal></entry>
+        <entry><literal>RN</literal> or <literal>rn</literal></entry>
-        <entry>Roman numeral (input between 1 and 3999)</entry>
+        <entry>Roman numeral (values between 1 and 3999)</entry>
        </row>
        <row>
         <entry><literal>TH</literal> or <literal>th</literal></entry>
@@ -8798,6 +8798,19 @@ SELECT regexp_match('abc01234xyz', '(?:(.*?)(\d+)(.*)){1,1}');
        (e.g., <literal>9.99EEEE</literal> is a valid pattern).
       </para>
      </listitem>
+
+     <listitem>
+      <para>
+       In <function>to_number()</function>, the <literal>RN</literal>
+       pattern converts Roman numerals (in standard form) to numbers.
+       Input is case-insensitive, so <literal>RN</literal>
+       and <literal>rn</literal> are equivalent.  <literal>RN</literal>
+       cannot be used in combination with any other formatting patterns or
+       modifiers except <literal>FM</literal>, which is applicable only
+       in <function>to_char()</function> and is ignored
+       in <function>to_number()</function>.
+      </para>
+     </listitem>
     </itemizedlist>
    </para>
 

src/backend/utils/adt/formatting.c

@@ -49,7 +49,6 @@
  *	- better number building (formatting) / parsing, now it isn't
  *		  ideal code
  *	- use Assert()
- *	- add support for roman number to standard number conversion
  *	- add support for number spelling
  *	- add support for string to string formatting (we must be better
  *	  than Oracle :-),
@@ -257,13 +256,39 @@ static const char *const rm_months_lower[] =
 {"xii", "xi", "x", "ix", "viii", "vii", "vi", "v", "iv", "iii", "ii", "i", NULL};
 
 /* ----------
- * Roman numbers
+ * Roman numerals
  * ----------
  */
 static const char *const rm1[] = {"I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX", NULL};
 static const char *const rm10[] = {"X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC", NULL};
 static const char *const rm100[] = {"C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM", NULL};
 
+/*
+ * MACRO: Check if the current and next characters form a valid subtraction
+ * combination for roman numerals.
+ */
+#define IS_VALID_SUB_COMB(curr, next) \
+	(((curr) == 'I' && ((next) == 'V' || (next) == 'X')) || \
+	 ((curr) == 'X' && ((next) == 'L' || (next) == 'C')) || \
+	 ((curr) == 'C' && ((next) == 'D' || (next) == 'M')))
+
+/*
+ * MACRO: Roman numeral value, or 0 if character isn't a roman numeral.
+ */
+#define ROMAN_VAL(r) \
+	((r) == 'I' ? 1 : \
+	 (r) == 'V' ? 5 : \
+	 (r) == 'X' ? 10 : \
+	 (r) == 'L' ? 50 : \
+	 (r) == 'C' ? 100 : \
+	 (r) == 'D' ? 500 : \
+	 (r) == 'M' ? 1000 : 0)
+
+/*
+ * 'MMMDCCCLXXXVIII' (3888) is the longest valid roman numeral (15 characters).
+ */
+#define MAX_ROMAN_LEN	15
+
 /* ----------
  * Ordinal postfixes
  * ----------
@@ -1028,6 +1053,15 @@ typedef struct NUMProc
 #define DCH_TIMED	0x02
 #define DCH_ZONED	0x04
 
+/*
+ * These macros are used in NUM_processor() and its subsidiary routines.
+ * OVERLOAD_TEST: true if we've reached end of input string
+ * AMOUNT_TEST(s): true if at least s bytes remain in string
+ */
+#define OVERLOAD_TEST	(Np->inout_p >= Np->inout + input_len)
+#define AMOUNT_TEST(s)	(Np->inout_p <= Np->inout + (input_len - (s)))
+
+
 /* ----------
  * Functions
  * ----------
@@ -1075,6 +1109,7 @@ static bool do_to_timestamp(text *date_txt, text *fmt, Oid collid, bool std,
 static char *fill_str(char *str, int c, int max);
 static FormatNode *NUM_cache(int len, NUMDesc *Num, text *pars_str, bool *shouldFree);
 static char *int_to_roman(int number);
+static int	roman_to_int(NUMProc *Np, int input_len);
 static void NUM_prepare_locale(NUMProc *Np);
 static char *get_last_relevant_decnum(char *num);
 static void NUM_numpart_from_char(NUMProc *Np, int id, int input_len);
@@ -1285,6 +1320,10 @@ NUMDesc_prepare(NUMDesc *num, FormatNode *n)
 
 		case NUM_rn:
 		case NUM_RN:
+			if (IS_ROMAN(num))
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("cannot use \"RN\" twice")));
 			num->flag |= NUM_F_ROMAN;
 			break;
 
@@ -1316,6 +1355,13 @@ NUMDesc_prepare(NUMDesc *num, FormatNode *n)
 			num->flag |= NUM_F_EEEE;
 			break;
 	}
+
+	if (IS_ROMAN(num) &&
+		(num->flag & ~(NUM_F_ROMAN | NUM_F_FILLMODE)) != 0)
+		ereport(ERROR,
+				(errcode(ERRCODE_SYNTAX_ERROR),
+				 errmsg("\"RN\" is incompatible with other formats"),
+				 errdetail("\"RN\" may only be used together with \"FM\".")));
 }
 
 /* ----------
@@ -4956,7 +5002,7 @@ int_to_roman(int number)
 			   *result,
 				numstr[12];
 
-	result = (char *) palloc(16);
+	result = (char *) palloc(MAX_ROMAN_LEN + 1);
 	*result = '\0';
 
 	/*
@@ -4966,7 +5012,7 @@ int_to_roman(int number)
 	 */
 	if (number > 3999 || number < 1)
 	{
-		fill_str(result, '#', 15);
+		fill_str(result, '#', MAX_ROMAN_LEN);
 		return result;
 	}
 
@@ -5000,6 +5046,157 @@ int_to_roman(int number)
 	return result;
 }
 
+/*
+ * Convert a roman numeral (standard form) to an integer.
+ * Result is an integer between 1 and 3999.
+ * Np->inout_p is advanced past the characters consumed.
+ *
+ * If input is invalid, return -1.
+ */
+static int
+roman_to_int(NUMProc *Np, int input_len)
+{
+	int			result = 0;
+	int			len;
+	char		romanChars[MAX_ROMAN_LEN];
+	int			romanValues[MAX_ROMAN_LEN];
+	int			repeatCount = 1;
+	int			vCount = 0,
+				lCount = 0,
+				dCount = 0;
+	bool		subtractionEncountered = false;
+	int			lastSubtractedValue = 0;
+
+	/*
+	 * Skip any leading whitespace.  Perhaps we should limit the amount of
+	 * space skipped to MAX_ROMAN_LEN, but that seems unnecessarily picky.
+	 */
+	while (!OVERLOAD_TEST && isspace((unsigned char) *Np->inout_p))
+		Np->inout_p++;
+
+	/*
+	 * Collect and decode valid roman numerals, consuming at most
+	 * MAX_ROMAN_LEN characters.  We do this in a separate loop to avoid
+	 * repeated decoding and because the main loop needs to know when it's at
+	 * the last numeral.
+	 */
+	for (len = 0; len < MAX_ROMAN_LEN && !OVERLOAD_TEST; len++)
+	{
+		char		currChar = pg_ascii_toupper(*Np->inout_p);
+		int			currValue = ROMAN_VAL(currChar);
+
+		if (currValue == 0)
+			break;				/* Not a valid roman numeral. */
+		romanChars[len] = currChar;
+		romanValues[len] = currValue;
+		Np->inout_p++;
+	}
+
+	if (len == 0)
+		return -1;				/* No valid roman numerals. */
+
+	/* Check for valid combinations and compute the represented value. */
+	for (int i = 0; i < len; i++)
+	{
+		char		currChar = romanChars[i];
+		int			currValue = romanValues[i];
+
+		/*
+		 * Ensure no numeral greater than or equal to the subtracted numeral
+		 * appears after a subtraction.
+		 */
+		if (subtractionEncountered && currValue >= lastSubtractedValue)
+			return -1;
+
+		/*
+		 * V, L, and D should not appear before a larger numeral, nor should
+		 * they be repeated.
+		 */
+		if ((vCount && currValue >= ROMAN_VAL('V')) ||
+			(lCount && currValue >= ROMAN_VAL('L')) ||
+			(dCount && currValue >= ROMAN_VAL('D')))
+			return -1;
+		if (currChar == 'V')
+			vCount++;
+		else if (currChar == 'L')
+			lCount++;
+		else if (currChar == 'D')
+			dCount++;
+
+		if (i < len - 1)
+		{
+			/* Compare current numeral to next numeral. */
+			char		nextChar = romanChars[i + 1];
+			int			nextValue = romanValues[i + 1];
+
+			/*
+			 * If the current value is less than the next value, handle
+			 * subtraction. Verify valid subtractive combinations and update
+			 * the result accordingly.
+			 */
+			if (currValue < nextValue)
+			{
+				if (!IS_VALID_SUB_COMB(currChar, nextChar))
+					return -1;
+
+				/*
+				 * Reject cases where same numeral is repeated with
+				 * subtraction (e.g. 'MCCM' or 'DCCCD').
+				 */
+				if (repeatCount > 1)
+					return -1;
+
+				/*
+				 * We are going to skip nextChar, so first make checks needed
+				 * for V, L, and D.  These are the same as we'd have applied
+				 * if we reached nextChar without a subtraction.
+				 */
+				if ((vCount && nextValue >= ROMAN_VAL('V')) ||
+					(lCount && nextValue >= ROMAN_VAL('L')) ||
+					(dCount && nextValue >= ROMAN_VAL('D')))
+					return -1;
+				if (nextChar == 'V')
+					vCount++;
+				else if (nextChar == 'L')
+					lCount++;
+				else if (nextChar == 'D')
+					dCount++;
+
+				/*
+				 * Skip the next numeral as it is part of the subtractive
+				 * combination.
+				 */
+				i++;
+
+				/* Update state. */
+				repeatCount = 1;
+				subtractionEncountered = true;
+				lastSubtractedValue = currValue;
+				result += (nextValue - currValue);
+			}
+			else
+			{
+				/* For same numerals, check for repetition. */
+				if (currChar == nextChar)
+				{
+					repeatCount++;
+					if (repeatCount > 3)
+						return -1;
+				}
+				else
+					repeatCount = 1;
+				result += currValue;
+			}
+		}
+		else
+		{
+			/* This is the last numeral; just add it to the result. */
+			result += currValue;
+		}
+	}
+
+	return result;
+}
 
 
 /* ----------
@@ -5112,14 +5309,6 @@ get_last_relevant_decnum(char *num)
 	return result;
 }
 
-/*
- * These macros are used in NUM_processor() and its subsidiary routines.
- * OVERLOAD_TEST: true if we've reached end of input string
- * AMOUNT_TEST(s): true if at least s bytes remain in string
- */
-#define OVERLOAD_TEST	(Np->inout_p >= Np->inout + input_len)
-#define AMOUNT_TEST(s)	(Np->inout_p <= Np->inout + (input_len - (s)))
-
 /* ----------
  * Number extraction for TO_NUMBER()
  * ----------
@@ -5576,29 +5765,6 @@ NUM_processor(FormatNode *node, NUMDesc *Num, char *inout,
 		return strcpy(inout, number);
 	}
 
-	/*
-	 * Roman correction
-	 */
-	if (IS_ROMAN(Np->Num))
-	{
-		if (!Np->is_to_char)
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("\"RN\" not supported for input")));
-
-		Np->Num->lsign = Np->Num->pre_lsign_num = Np->Num->post =
-			Np->Num->pre = Np->out_pre_spaces = Np->sign = 0;
-
-		if (IS_FILLMODE(Np->Num))
-		{
-			Np->Num->flag = 0;
-			Np->Num->flag |= NUM_F_FILLMODE;
-		}
-		else
-			Np->Num->flag = 0;
-		Np->Num->flag |= NUM_F_ROMAN;
-	}
-
 	/*
 	 * Sign
 	 */
@@ -5849,28 +6015,35 @@ NUM_processor(FormatNode *node, NUMDesc *Num, char *inout,
 					break;
 
 				case NUM_RN:
-					if (IS_FILLMODE(Np->Num))
-					{
-						strcpy(Np->inout_p, Np->number_p);
-						Np->inout_p += strlen(Np->inout_p) - 1;
-					}
-					else
-					{
-						sprintf(Np->inout_p, "%15s", Np->number_p);
-						Np->inout_p += strlen(Np->inout_p) - 1;
-					}
-					break;
-
 				case NUM_rn:
-					if (IS_FILLMODE(Np->Num))
+					if (Np->is_to_char)
 					{
-						strcpy(Np->inout_p, asc_tolower_z(Np->number_p));
+						const char *number_p;
+
+						if (n->key->id == NUM_rn)
+							number_p = asc_tolower_z(Np->number_p);
+						else
+							number_p = Np->number_p;
+						if (IS_FILLMODE(Np->Num))
+							strcpy(Np->inout_p, number_p);
+						else
+							sprintf(Np->inout_p, "%15s", number_p);
 						Np->inout_p += strlen(Np->inout_p) - 1;
 					}
 					else
 					{
-						sprintf(Np->inout_p, "%15s", asc_tolower_z(Np->number_p));
+						int			roman_result = roman_to_int(Np, input_len);
-						Np->inout_p += strlen(Np->inout_p) - 1;
+						int			numlen;
+
+						if (roman_result < 0)
+							ereport(ERROR,
+									(errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
+									 errmsg("invalid Roman numeral")));
+						numlen = sprintf(Np->number_p, "%d", roman_result);
+						Np->number_p += numlen;
+						Np->Num->pre = numlen;
+						Np->Num->post = 0;
+						continue;	/* roman_to_int ate all the chars */
 					}
 					break;
 

src/test/regress/expected/numeric.out

@@ -2384,6 +2384,84 @@ SELECT to_number('123456', '99999V99');
  1234.560000000000000000
 (1 row)
 
+-- Test for correct conversion between numbers and Roman numerals
+WITH rows AS
+  (SELECT i, to_char(i, 'RN') AS roman FROM generate_series(1, 3999) AS i)
+SELECT
+  bool_and(to_number(roman, 'RN') = i) as valid
+FROM rows;
+ valid 
+-------
+ t
+(1 row)
+
+-- Some additional tests for RN input
+SELECT to_number('CvIiI', 'rn');
+ to_number 
+-----------
+       108
+(1 row)
+
+SELECT to_number('MMXX  ', 'RN');
+ to_number 
+-----------
+      2020
+(1 row)
+
+SELECT to_number('  XIV', '  RN');
+ to_number 
+-----------
+        14
+(1 row)
+
+SELECT to_number('  XIV  ', '  RN');
+ to_number 
+-----------
+        14
+(1 row)
+
+SELECT to_number('M CC', 'RN');
+ to_number 
+-----------
+      1000
+(1 row)
+
+-- error cases
+SELECT to_number('viv', 'RN');
+ERROR:  invalid Roman numeral
+SELECT to_number('DCCCD', 'RN');
+ERROR:  invalid Roman numeral
+SELECT to_number('XIXL', 'RN');
+ERROR:  invalid Roman numeral
+SELECT to_number('MCCM', 'RN');
+ERROR:  invalid Roman numeral
+SELECT to_number('MMMM', 'RN');
+ERROR:  invalid Roman numeral
+SELECT to_number('VV', 'RN');
+ERROR:  invalid Roman numeral
+SELECT to_number('IL', 'RN');
+ERROR:  invalid Roman numeral
+SELECT to_number('VIX', 'RN');
+ERROR:  invalid Roman numeral
+SELECT to_number('LXC', 'RN');
+ERROR:  invalid Roman numeral
+SELECT to_number('DCM', 'RN');
+ERROR:  invalid Roman numeral
+SELECT to_number('MMMDCM', 'RN');
+ERROR:  invalid Roman numeral
+SELECT to_number('CLXC', 'RN');
+ERROR:  invalid Roman numeral
+SELECT to_number('CM', 'MIRN');
+ERROR:  "RN" is incompatible with other formats
+DETAIL:  "RN" may only be used together with "FM".
+SELECT to_number('CM', 'RNRN');
+ERROR:  cannot use "RN" twice
+SELECT to_number('qiv', 'RN');
+ERROR:  invalid Roman numeral
+SELECT to_number('', 'RN');
+ERROR:  invalid input syntax for type numeric: " "
+SELECT to_number(' ', 'RN');
+ERROR:  invalid Roman numeral
 RESET lc_numeric;
 --
 -- Input syntax

src/test/regress/sql/numeric.sql

@@ -1085,6 +1085,39 @@ SELECT to_number('1234.56','L99,999.99');
 SELECT to_number('1,234.56','L99,999.99');
 SELECT to_number('42nd', '99th');
 SELECT to_number('123456', '99999V99');
+
+-- Test for correct conversion between numbers and Roman numerals
+WITH rows AS
+  (SELECT i, to_char(i, 'RN') AS roman FROM generate_series(1, 3999) AS i)
+SELECT
+  bool_and(to_number(roman, 'RN') = i) as valid
+FROM rows;
+
+-- Some additional tests for RN input
+SELECT to_number('CvIiI', 'rn');
+SELECT to_number('MMXX  ', 'RN');
+SELECT to_number('  XIV', '  RN');
+SELECT to_number('  XIV  ', '  RN');
+SELECT to_number('M CC', 'RN');
+-- error cases
+SELECT to_number('viv', 'RN');
+SELECT to_number('DCCCD', 'RN');
+SELECT to_number('XIXL', 'RN');
+SELECT to_number('MCCM', 'RN');
+SELECT to_number('MMMM', 'RN');
+SELECT to_number('VV', 'RN');
+SELECT to_number('IL', 'RN');
+SELECT to_number('VIX', 'RN');
+SELECT to_number('LXC', 'RN');
+SELECT to_number('DCM', 'RN');
+SELECT to_number('MMMDCM', 'RN');
+SELECT to_number('CLXC', 'RN');
+SELECT to_number('CM', 'MIRN');
+SELECT to_number('CM', 'RNRN');
+SELECT to_number('qiv', 'RN');
+SELECT to_number('', 'RN');
+SELECT to_number(' ', 'RN');
+
 RESET lc_numeric;
 
 --