Provide %b in #'format; use it for converting between ints and bit vectors. lisp/ChangeLog addition: 2007-12-17 Aidan Kehoe <kehoea@parhasard.net> * subr.el (integer-to-bit-vector): New. * subr.el (bit-vector-to-integer): New. Provide naive implementations using the Lisp reader for these. src/ChangeLog addition: 2007-12-17 Aidan Kehoe <kehoea@parhasard.net> * doprnt.c (emacs_doprnt_1): Add support for formatted printing of both longs and bignums as base 2. * editfns.c (Fformat): Document the new %b escape for #'format. * lisp.h: Make ulong_to_bit_string available beside long_to_string. * lread.c: Fix a bug where the integer base was being ignored in certain contexts; thank you Sebastian Freundt. This is necessary for correct behaviour of #'integer-to-bit-vector and #'bit-vector-to-integer, just added to subr.el * print.c (ulong_to_bit_string): New. Analagous to long_to_string, but used all the time when %b is encountered, since we can't pass that to sprintf. man/ChangeLog addition: 2007-12-17 Aidan Kehoe <kehoea@parhasard.net> * lispref/strings.texi (Formatting Strings): Document %b for binary output.

--- a/src/print.c	Fri Dec 14 14:25:04 2007 +0100
+++ b/src/print.c	Mon Dec 17 08:44:14 2007 +0100
@@ -1269,6 +1269,29 @@
 #undef DIGITS_18
 #undef DIGITS_19
 
+void
+ulong_to_bit_string (char *p, unsigned long number)
+{
+  int i, seen_high_order = 0;;
+  
+  for (i = ((SIZEOF_LONG * 8) - 1); i >= 0; --i)
+    {
+      if (number & (unsigned long)1 << i)
+        {
+          seen_high_order = 1;
+          *p++ = '1';
+        }
+      else
+        {
+          if (seen_high_order)
+            {
+              *p++ = '0';
+            }
+        }
+    }
+  *p = '\0';
+}
+
 static void
 print_vector_internal (const char *start, const char *end,
                        Lisp_Object obj,