In -Tascii mode, provide approximations even for some Unicode escape

sequences above codepoint 512 by doing a reverse lookup in the
existing mandoc_char(7) character table.

Again, groff isn't smart enough to do this and silently discards such
escape sequences without printing anything.

4 files changed, 27 insertions, 2 deletions

diff --git a/chars.c b/chars.c
index e11e64c9..950f9edc 100644
--- a/chars.c
+++ b/chars.c
@@ -149,6 +149,17 @@ mchars_spec2str(const struct mchars *arg,
 	return(ln->ascii);
 }
 
+const char *
+mchars_uc2str(int uc)
+{
+	int	 i;
+
+	for (i = 0; i < LINES_MAX; i++)
+		if (uc == lines[i].unicode)
+			return(lines[i].ascii);
+	return("<?>");
+}
+
 static const struct ln *
 find(const struct mchars *tab, const char *p, size_t sz)
 {
diff --git a/mandoc.h b/mandoc.h
index 14fddd36..5052a8b3 100644
--- a/mandoc.h
+++ b/mandoc.h
@@ -426,6 +426,7 @@ enum mandoc_esc	  mandoc_escape(const char **, const char **, int *);
 struct mchars	 *mchars_alloc(void);
 void		  mchars_free(struct mchars *);
 char		  mchars_num2char(const char *, size_t);
+const char	 *mchars_uc2str(int);
 int		  mchars_num2uc(const char *, size_t);
 int		  mchars_spec2cp(const struct mchars *,
 			const char *, size_t);
diff --git a/mchars_alloc.3 b/mchars_alloc.3
index 34c9fa3f..44442e4a 100644
--- a/mchars_alloc.3
+++ b/mchars_alloc.3
@@ -59,6 +59,8 @@
 .Fa "size_t sz"
 .Fa "size_t *rsz"
 .Fc
+.Ft "const char *"
+.Fn mchars_uc2str "int codepoint"
 .Sh DESCRIPTION
 These functions translate Unicode character numbers and
 .Xr roff 7
@@ -199,6 +201,14 @@ output module use this function to render
 and
 .Ic \eC\(aq Ns Ar name Ns Ic \(aq
 escape sequences.
+.Pp
+The function
+.Fn mchars_uc2str
+performs a reverse lookup of the Unicode
+.Fa codepoint
+and returns an ASCII string representation, or the string
+.Qq <?>
+if none is available.
 .Sh FILES
 These funtions are implemented in the file
 .Pa chars.c .
@@ -218,6 +228,7 @@ following mandoc versions:
 .It Fn mchars_num2uc Ta 1.11.3 Ta \(em Ta \(em
 .It Fn mchars_spec2cp Ta 1.11.2 Ta Fn chars_spec2cp Ta 1.10.5
 .It Fn mchars_spec2str Ta 1.11.2 Ta Fn a2ascii Ta 1.5.3
+.It Fn mchars_uc2str Ta 1.13.2 Ta \(em Ta \(em
 .El
 .Sh AUTHORS
 .An Kristaps Dzonsons Aq Mt kristaps@bsd.lv
diff --git a/term_ascii.c b/term_ascii.c
index d7283411..f5782ff2 100644
--- a/term_ascii.c
+++ b/term_ascii.c
@@ -236,9 +236,11 @@ ascii_uc2str(int uc)
 	"j",	"DZ",	"D",	"dz",	"G",	"g",	"HV",	"W",
 	"N",	"n",	"A",	"a",	"AE",	"ae",	"O",	"o"};
 
-	if (uc < 0 || (size_t)uc >= sizeof(tab)/sizeof(tab[0]))
+	if (uc < 0)
 		return("<?>");
-	return(tab[uc]);
+	if ((size_t)uc < sizeof(tab)/sizeof(tab[0]))
+		return(tab[uc]);
+	return(mchars_uc2str(uc));
 }
 
 static size_t