In terminal output, unify handling of Unicode and numbered character

escape sequences just like it was earlier implemented for -Thtml.
Do not let control characters other than ASCII 9 (horizontal tab)
propagate to the output, even though groff allows them; but that
really doesn't look like a great idea.

Let mchars_num2char() return int such that we can distinguish invalid \N
syntax from \N'0'.  This also reduces the danger of signed char issues
popping up.

1 files changed, 6 insertions, 3 deletions

diff --git a/html.c b/html.c
index 01514937..ff68e6e1 100644
--- a/html.c
+++ b/html.c
@@ -422,9 +422,13 @@ print_encode(struct html *h, const char *p, int norecurse)
 			break;
 		case ESCAPE_NUMBERED:
 			c = mchars_num2char(seq, len);
+			if (c < 0)
+				continue;
 			break;
 		case ESCAPE_SPECIAL:
 			c = mchars_spec2cp(h->symtab, seq, len);
+			if (c <= 0)
+				continue;
 			break;
 		case ESCAPE_NOSPACE:
 			if ('\0' == *p)
@@ -433,9 +437,8 @@ print_encode(struct html *h, const char *p, int norecurse)
 		default:
 			continue;
 		}
-		if (c <= 0)
-			continue;
-		if (c < 0x20 || (c > 0x7E && c < 0xA0))
+		if ((c < 0x20 && c != 0x09) ||
+		    (c > 0x7E && c < 0xA0))
 			c = 0xFFFD;
 		if (c > 0x7E)
 			printf("&#%d;", c);