%o and %x can now format signed integers

Optionally treat integers as signed numbers with %o
and %x format specifiers, instead of treating them as
a machine-dependent two’s complement representation.
This option is more machine-independent, allows formats
like "#x%x" to be useful for reading later, and is
better-insulated for future changes involving bignums.
Setting the new variable ‘binary-as-unsigned’ to nil
enables the new behavior (Bug#32252).
This is a simplified version of the change proposed in:
https://lists.gnu.org/r/emacs-devel/2018-07/msg00763.html
I simplified that proposal by omitting bitwidth modifiers, as
I could not find an any example uses in the Emacs source code
that needed them and doing them correctly would have been
quite a bit more work for apparently little benefit.
* doc/lispref/strings.texi (Formatting Strings):
Document that %x and %o format negative integers in a
platform-dependent way.  Also, document how to format
numbers so that the same values can be read back in.
* etc/NEWS: Document the change.
* src/editfns.c (styled_format): Treat integers as signed
numbers even with %o and %x, if binary-as-unsigned is nil.
Support the + and space flags with %o and %x, since they’re
about signs.
(syms_of_editfns): New variable binary-as-unsigned.
* test/src/editfns-tests.el (read-large-integer):
Test that maximal integers can be read after printing
with all integer formats, if binary-as-unsigned is nil.

1 files changed, 6 insertions, 4 deletions

diff --git a/test/src/editfns-tests.el b/test/src/editfns-tests.el
index c828000bb4f..2951270dbf7 100644
--- a/test/src/editfns-tests.el
+++ b/test/src/editfns-tests.el
@@ -165,10 +165,12 @@
                 :type 'overflow-error)
   (should-error (read (substring (format "%d" most-negative-fixnum) 1))
                 :type 'overflow-error)
-  (should-error (read (format "#x%x" most-negative-fixnum))
-                :type 'overflow-error)
-  (should-error (read (format "#o%o" most-negative-fixnum))
-                :type 'overflow-error)
+  (let ((binary-as-unsigned nil))
+    (dolist (fmt '("%d" "%s" "#o%o" "#x%x"))
+      (dolist (val (list most-negative-fixnum (1+ most-negative-fixnum)
+                         -1 0 1
+                         (1- most-positive-fixnum) most-positive-fixnum))
+        (should (eq val (read (format fmt val)))))))
   (should-error (read (format "#32rG%x" most-positive-fixnum))
                 :type 'overflow-error))