chr-iscntrl: recognize Unicode C0 and C1.

* lib.c (chr_iscntrl): Don't use iswcntrl; it fails to report
0x80-0x9F as control characters. A bit of hand-crafted logic
does the job.

* txr.1: Redocumented.

2 files changed, 13 insertions, 4 deletions

diff --git a/lib.c b/lib.c
index 11ad76b5..38837e43 100644
--- a/lib.c
+++ b/lib.c
@@ -5897,7 +5897,13 @@ val chr_isascii(val ch)
 
 val chr_iscntrl(val ch)
 {
-  return tnil(iswcntrl(c_chr(ch)));
+  wchar_t c = c_chr(ch);
+  switch ((c >> 5)) {
+  case 0: case 4:
+    return t;
+  default:
+    return tnil(c == 0x7F);
+  }
 }
 
 val chr_isdigit(val ch)
diff --git a/txr.1 b/txr.1
index 9de10070..de1e1912 100644
--- a/txr.1
+++ b/txr.1
@@ -24586,11 +24586,14 @@ function returns
 .code t
 if the character
 .meta char
-is a character whose code
-ranges from 0 to 31, or is 127. In other words, any non-printable ASCII
-character. For other characters, it returns
+is a control character. For all other character, it returns
 .codn nil .
 
+A control character is one which belongs to the Unicode C0 or C1 block.
+C0 consists of the the characters U+0000 through U+001F, plus the
+character U+007F. These are the original ASCII control characters.
+Block C1 consists of U+0080 through U+009F.
+
 .coNP Functions @ chr-isdigit and @ chr-digit
 .synb
 .mets (chr-isdigit << char )