Fix psql's code for locale-aware formatting of numeric output.

This code did the wrong thing entirely for numbers with an exponent
but no decimal point (e.g., '1e6'), as reported by Jeff Janes in
bug #13636.  More generally, it made lots of unverified assumptions
about what the input string could possibly look like.  Rearrange so
that it only fools with leading digits that it's directly verified
are there, and an immediately adjacent decimal point.  While at it,
get rid of some useless inefficiencies, like converting the grouping
count string to integer over and over (and over).

This has been broken for a long time, so back-patch to all supported
branches.

src/bin/psql/print.c

@@ -39,8 +39,9 @@
  */
 volatile bool cancel_pressed = false;
 
+/* info for locale-aware numeric formatting; set up by setDecimalLocale() */
 static char *decimal_point;
-static char *grouping;
+static int	groupdigits;
 static char *thousands_sep;
 
 static char default_footer[100];
@@ -196,44 +197,35 @@ static void IsPagerNeeded(const printTableContent *cont, const int extra_lines,
 static void print_aligned_vertical(const printTableContent *cont, FILE *fout);
 
 
+/* Count number of digits in integral part of number */
 static int
 integer_digits(const char *my_str)
 {
-	int			frac_len;
-
-	if (my_str[0] == '-')
+	/* ignoring any sign ... */
+	if (my_str[0] == '-' || my_str[0] == '+')
 		my_str++;
-
-	frac_len = strchr(my_str, '.') ? strlen(strchr(my_str, '.')) : 0;
-
-	return strlen(my_str) - frac_len;
+	/* ... count initial integral digits */
+	return strspn(my_str, "0123456789");
 }
 
-/* Return additional length required for locale-aware numeric output */
+/* Compute additional length required for locale-aware numeric output */
 static int
 additional_numeric_locale_len(const char *my_str)
 {
 	int			int_len = integer_digits(my_str),
 				len = 0;
-	int			groupdigits = atoi(grouping);
 
-	if (int_len > 0)
-		/* Don't count a leading separator */
-		len = (int_len / groupdigits - (int_len % groupdigits == 0)) *
-			strlen(thousands_sep);
+	/* Account for added thousands_sep instances */
+	if (int_len > groupdigits)
+		len += ((int_len - 1) / groupdigits) * strlen(thousands_sep);
 
+	/* Account for possible additional length of decimal_point */
 	if (strchr(my_str, '.') != NULL)
-		len += strlen(decimal_point) - strlen(".");
+		len += strlen(decimal_point) - 1;
 
 	return len;
 }
 
-static int
-strlen_with_numeric_locale(const char *my_str)
-{
-	return strlen(my_str) + additional_numeric_locale_len(my_str);
-}
-
 /*
  * Returns the appropriately formatted string in a new allocated block,
  * caller must free
@@ -241,53 +233,51 @@ strlen_with_numeric_locale(const char *my_str)
 static char *
 format_numeric_locale(const char *my_str)
 {
+	int			new_len = strlen(my_str) + additional_numeric_locale_len(my_str);
+	char	   *new_str = pg_malloc(new_len + 1);
+	int			int_len = integer_digits(my_str);
 	int			i,
-				j,
-				int_len = integer_digits(my_str),
 				leading_digits;
-	int			groupdigits = atoi(grouping);
-	int			new_str_start = 0;
-	char	   *new_str = pg_malloc(strlen_with_numeric_locale(my_str) + 1);
+	int			new_str_pos = 0;
 
-	leading_digits = (int_len % groupdigits != 0) ?
-		int_len % groupdigits : groupdigits;
+	/* number of digits in first thousands group */
+	leading_digits = int_len % groupdigits;
+	if (leading_digits == 0)
+		leading_digits = groupdigits;
 
-	if (my_str[0] == '-')		/* skip over sign, affects grouping
-								 * calculations */
+	/* process sign */
+	if (my_str[0] == '-' || my_str[0] == '+')
 	{
-		new_str[0] = my_str[0];
+		new_str[new_str_pos++] = my_str[0];
 		my_str++;
-		new_str_start = 1;
 	}
 
-	for (i = 0, j = new_str_start;; i++, j++)
+	/* process integer part of number */
+	for (i = 0; i < int_len; i++)
 	{
-		/* Hit decimal point? */
-		if (my_str[i] == '.')
+		/* Time to insert separator? */
+		if (i > 0 && --leading_digits == 0)
 		{
-			strcpy(&new_str[j], decimal_point);
-			j += strlen(decimal_point);
-			/* add fractional part */
-			strcpy(&new_str[j], &my_str[i] + 1);
-			break;
+			strcpy(&new_str[new_str_pos], thousands_sep);
+			new_str_pos += strlen(thousands_sep);
+			leading_digits = groupdigits;
 		}
+		new_str[new_str_pos++] = my_str[i];
+	}
 
-		/* End of string? */
-		if (my_str[i] == '\0')
-		{
-			new_str[j] = '\0';
-			break;
-		}
+	/* handle decimal point if any */
+	if (my_str[i] == '.')
+	{
+		strcpy(&new_str[new_str_pos], decimal_point);
+		new_str_pos += strlen(decimal_point);
+		i++;
+	}
 
-		/* Add separator? */
-		if (i != 0 && (i - leading_digits) % groupdigits == 0)
-		{
-			strcpy(&new_str[j], thousands_sep);
-			j += strlen(thousands_sep);
-		}
+	/* copy the rest (fractional digits and/or exponent, and \0 terminator) */
+	strcpy(&new_str[new_str_pos], &my_str[i]);
 
-		new_str[j] = my_str[i];
-	}
+	/* assert we didn't underestimate new_len (an overestimate is OK) */
+	Assert(strlen(new_str) <= new_len);
 
 	return new_str;
 }
@@ -3241,10 +3231,11 @@ setDecimalLocale(void)
 		decimal_point = pg_strdup(extlconv->decimal_point);
 	else
 		decimal_point = ".";	/* SQL output standard */
+
 	if (*extlconv->grouping && atoi(extlconv->grouping) > 0)
-		grouping = pg_strdup(extlconv->grouping);
+		groupdigits = atoi(extlconv->grouping);
 	else
-		grouping = "3";			/* most common */
+		groupdigits = 3;		/* most common */
 
 	/* similar code exists in formatting.c */
 	if (*extlconv->thousands_sep)