bug#29609: 27.0.50; Format number as hexadecimal with hash-flag

bug#29609: 27.0.50; Format number as hexadecimal with hash-flag

[Gustaf Waldemarson]

Hello,

I recently noticed that the `format` function behaves incorrectly when
formatting numbers as hexadecimal together with the hash-flag. E.g.,
following this recipe yields:

1. M-x ielm
2. Evaluate: (format "%#08x" #x10) -> "00000x10"

Typically Bash, C and other formatting implementations typically formats
this as "0x00000010", and I think Emacs should do the same in this case.

This seems to be present in a few different versions of Emacs, I've
tried it on 24.5.1 and 27.0.50 and they both behave the same.

Regards,
Gustaf


In GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.11)
 of 2017-11-29 built on ShadowX
Repository revision: 95369ac346d75a7b75bc2c5adf632cc4faa1241a
Windowing system distributor 'The X.Org Foundation', version 11.0.11903000
System Description:    Ubuntu 17.04

Recent messages:
scroll-down-command: Beginning of buffer
Mark set (rectangle mode)
When done with a buffer, type C-x #
Configuring package message...done
Configuring package git-commit...done
Configuring package magit...done [2 times]
When done with a buffer, type C-x # [2 times]
Making completion list... [2 times]
delete-backward-char: Text is read-only
Making completion list...

Configured using:
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 '--program-transform-name=s/^ctags$/ctags.emacs/''

Configured features:
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GNUTLS LIBXML2 FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 LCMS2

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Load-path shadows:
None found.

Features:
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magit-wip magit-log magit-diff smerge-mode diff-mode magit-core
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Memory information:
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 (symbols 48 49359 3)
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bug#29609: 27.0.50; Format number as hexadecimal with hash-flag

[Paul Eggert]

[-- Attachment #1: Type: text/plain, Size: 79 bytes --]

Thanks for reporting that. I installed the attached, which should fix the bug.

[-- Attachment #2: 0001-Fix-zero-padding-bug-with-format-08x-n.patch --]
[-- Type: text/x-patch, Size: 2700 bytes --]

From 47423f0603f2ecfb78352be5477fb02c44f1fd35 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Thu, 7 Dec 2017 18:07:54 -0800
Subject: [PATCH] Fix zero-padding bug with (format "%#08x" n)

Problem reported by Gustaf Waldemarson (Bug#29609).
* src/editfns.c (styled_format):
Put zero padding after a leading "0x", not before.
* test/src/editfns-tests.el (format-sharp-0-x): New test.
---
 src/editfns.c             | 24 ++++++++++++++++--------
 test/src/editfns-tests.el |  6 ++++++
 2 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/src/editfns.c b/src/editfns.c
index e671ba0..ebf6518 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -4722,11 +4722,19 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
 		  char src0 = src[0];
 		  int exponent_bytes = 0;
 		  bool signedp = src0 == '-' || src0 == '+' || src0 == ' ';
-		  unsigned char after_sign = src[signedp];
-		  if (zero_flag && 0 <= char_hexdigit (after_sign))
+		  int prefix_bytes = (signedp
+				      + ((src[signedp] == '0'
+					  && (src[signedp + 1] == 'x'
+					      || src[signedp + 1] == 'X'))
+					 ? 2 : 0));
+		  if (zero_flag)
 		    {
-		      leading_zeros += padding;
-		      padding = 0;
+		      unsigned char after_prefix = src[prefix_bytes];
+		      if (0 <= char_hexdigit (after_prefix))
+			{
+			  leading_zeros += padding;
+			  padding = 0;
+			}
 		    }
 
 		  if (excess_precision
@@ -4745,13 +4753,13 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
 		      nchars += padding;
 		    }
 
-		  *p = src0;
-		  src += signedp;
-		  p += signedp;
+		  memcpy (p, src, prefix_bytes);
+		  p += prefix_bytes;
+		  src += prefix_bytes;
 		  memset (p, '0', leading_zeros);
 		  p += leading_zeros;
 		  int significand_bytes
-		    = sprintf_bytes - signedp - exponent_bytes;
+		    = sprintf_bytes - prefix_bytes - exponent_bytes;
 		  memcpy (p, src, significand_bytes);
                   p += significand_bytes;
 		  src += significand_bytes;
diff --git a/test/src/editfns-tests.el b/test/src/editfns-tests.el
index 70dc937..283a642 100644
--- a/test/src/editfns-tests.el
+++ b/test/src/editfns-tests.el
@@ -136,6 +136,12 @@ transpose-test-get-byte-positions
 (ert-deftest format-c-float ()
   (should-error (format "%c" 0.5)))
 
+;;; Test for Bug#29609.
+(ert-deftest format-sharp-0-x ()
+  (should (string-equal (format "%#08x" #x10) "0x000010"))
+  (should (string-equal (format "%#05X" #x10) "0X010"))
+  (should (string-equal (format "%#04x" 0) "0000")))
+
 ;;; Check format-time-string with various TZ settings.
 ;;; Use only POSIX-compatible TZ values, since the tests should work
 ;;; even if tzdb is not in use.
-- 
2.7.4

bug#29609: 27.0.50; Format number as hexadecimal with hash-flag

[Glenn Morris]

Since 47423f0, three bootstraps in a row have failed for me on RHEL7.4,
with a segfault at some random point in the build. Eg:
    
    /bin/sh: line 1: 26588 Segmentation fault      (core dumped)
    EMACSLOADPATH= '../src/emacs' -batch --no-site-file --no-site-lisp
     --eval '(setq load-prefer-newer t)' -f batch-byte-compile
    calc/calc-keypd.el
    make[2]: *** [calc/calc-keypd.elc] Error 139

Could be a coincidence, but before this change I haven't had such
failures. Could there be something wrong with 47423f0?

bug#29609: 27.0.50; Format number as hexadecimal with hash-flag

[Paul Eggert]

[-- Attachment #1: Type: text/plain, Size: 203 bytes --]

On 12/08/2017 09:51 AM, Glenn Morris wrote:
> Could there be something wrong with 47423f0?

Yes there could, and thanks for reporting it. I installed the attached 
to fix the bug I recently introduced.


[-- Attachment #2: 0001-Fix-core-dump-from-format-08x-n-patch.patch --]
[-- Type: text/x-patch, Size: 859 bytes --]

From c9d450ffcc755c4af39c2ab5a9e585f05eeddf94 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Fri, 8 Dec 2017 13:30:06 -0800
Subject: [PATCH] Fix core dump from (format "%#08x" n) patch

Problem reported by Glenn Morris (Bug#29609#13).
* src/editfns.c (styled_format): Null-terminate output,
as later code now expects this.
---
 src/editfns.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/editfns.c b/src/editfns.c
index ebf6518994..084d92346f 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -4623,6 +4623,7 @@ styled_format (ptrdiff_t nargs, Lisp_Object *args, bool message)
 		  /* Don't use sprintf here, as it might mishandle prec.  */
 		  sprintf_buf[0] = XINT (arg);
 		  sprintf_bytes = prec != 0;
+		  sprintf_buf[sprintf_bytes] = '\0';
 		}
 	      else if (conversion == 'd' || conversion == 'i')
 		{
-- 
2.14.3