From 5335d788dc601a50fc26319d39b21bdcaf1457b6 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Wed, 23 Dec 2015 06:58:09 -0800
Subject: chr-isdigit and chr-isxdigit return value.

* lib.c (chr_isdigit, chr_isxdigit): Return the integer value
rather than the symbol t, which can be exploited to write
more compact scanning code.

* txr.1: Documented.
---
 lib.c | 15 +++++++++++++--
 txr.1 | 35 ++++++++++++++++++++++-------------
 2 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/lib.c b/lib.c
index 05ccb45a..2aa5029d 100644
--- a/lib.c
+++ b/lib.c
@@ -4025,7 +4025,7 @@ val chr_iscntrl(val ch)
 
 val chr_isdigit(val ch)
 {
-  return tnil(iswdigit(c_chr(ch)));
+  return if2(iswdigit(c_chr(ch)), minus(ch, chr('0')));
 }
 
 val chr_isgraph(val ch)
@@ -4070,7 +4070,18 @@ val chr_isupper(val ch)
 
 val chr_isxdigit(val ch)
 {
-  return tnil(iswxdigit(c_chr(ch)));
+  wchar_t cc = c_chr(ch);
+
+  if ('0' <= cc && cc <= '9')
+    return num_fast(cc - '0');
+
+  if ('A' <= cc && cc <= 'F')
+    return num_fast(cc - 'A' + 10);
+
+  if ('a' <= cc && cc <= 'a')
+    return num_fast(cc - 'a' + 10);
+
+  return nil;
 }
 
 val chr_toupper(val ch)
diff --git a/txr.1 b/txr.1
index 27e72bcd..003ace07 100644
--- a/txr.1
+++ b/txr.1
@@ -17646,11 +17646,11 @@ character. For other characters, it returns
 .mets (chr-isdigit << char )
 .syne
 .desc
-This function returns
-.code t
-if the character
+If
 .meta char
-is is an ASCII digit.
+is is an ASCII digit character,
+.code chr-isdigit
+returns the integer value, 0 to 9, corresponding to that character.
 Otherwise, it returns
 .codn nil .
 
@@ -17803,19 +17803,28 @@ is an ASCII upper case letter. Otherwise it returns
 .mets (chr-isxdigit << char )
 .syne
 .desc
-This function returns
-.code t
-if
+If
 .meta char
-is a hexadecimal digit. One of the ASCII
-letters
+is a hexadecimal digit character,
+.code chr-isxdigit
+returns its integer value 0 to 15.
+Otherwise it returns
+.codn nil  .
+
+A hexadecimal digit is one of the ASCII
+digit characters
+.code 0
+through
+.codn 9 ,
+or else one of the letters
 .code A
 through
-.codn F ,
-or their lower-case equivalents, or an ASCII digit
-.code 0
+.code F
+or their lower-case equivalents
+.code a
 through
-.codn 9 .
+.code f
+denoting the values 10 to 15.
 
 .coNP Function @ chr-toupper
 .synb
-- 
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