GNU bug report logs - #16283
24.2; Built-in function * , used for calculating product, gives wrong output

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Mohammed Sami <abdussami101 <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.2; Built-in function * , used for calculating product, gives wrong
 output
Date: Sat, 28 Dec 2013 23:45:38 +0530

[Message part 1 (text/plain, inline)]

Please describe exactly what actions triggered the bug, and
the precise symptoms of the bug.  If you can, give a recipe
starting from `emacs -Q':

After starting window Emacs with "emacs -q", when I evaluate (* 1024 1024
1024 1024), I get 0.
(* 1024 1024) works correctly, but repeating '1024' more than two times
gives wrong value.

In GNU Emacs 24.2.1 (i386-mingw-nt5.1.2600)
 of 2012-08-29 on MARVIN
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.6) --cflags
 -ID:/devel/emacs/libs/libXpm-3.5.8/include
 -ID:/devel/emacs/libs/libXpm-3.5.8/src
 -ID:/devel/emacs/libs/libpng-dev_1.4.3-1/include
 -ID:/devel/emacs/libs/zlib-dev_1.2.5-2/include
 -ID:/devel/emacs/libs/giflib-4.1.4-1/include
 -ID:/devel/emacs/libs/jpeg-6b-4/include
 -ID:/devel/emacs/libs/tiff-3.8.2-1/include
 -ID:/devel/emacs/libs/gnutls-3.0.9/include'

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: ENU
  value of $XMODIFIERS: nil
  locale-coding-system: cp1252
  default enable-multibyte-characters: t

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
C-x b s c <return> M-< M-> ( * SPC 1 0 2 4 SPC 1 0
2 4 SPC 1 0 2 4 SPC 1 0 2 4 ) C-u C-x C-e <help-echo>
<return> M-x r e p o r t <tab> <return>



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Message #8 received at 16283 <at> debbugs.gnu.org (full text, mbox):

From: Andreas Schwab <schwab <at> linux-m68k.org>
To: Mohammed Sami <abdussami101 <at> gmail.com>
Cc: 16283 <at> debbugs.gnu.org
Subject: Re: bug#16283: 24.2;
 Built-in function * , used for calculating product, gives wrong output
Date: Sat, 28 Dec 2013 19:51:32 +0100

Mohammed Sami <abdussami101 <at> gmail.com> writes:

> After starting window Emacs with "emacs -q", when I evaluate (* 1024 1024
> 1024 1024), I get 0.

Arithmetic functions generally don't check for overflow.

Andreas.

-- 
Andreas Schwab, schwab <at> linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Message #13 received at 16283-done <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Mohammed Sami <abdussami101 <at> gmail.com>
Cc: 16283-done <at> debbugs.gnu.org
Subject: Re: bug#16283: 24.2;
 Built-in function * , used for calculating product, gives wrong output
Date: Sat, 28 Dec 2013 20:52:02 +0200

> From: Mohammed Sami <abdussami101 <at> gmail.com>
> Date: Sat, 28 Dec 2013 23:45:38 +0530
> 
> After starting window Emacs with "emacs -q", when I evaluate (* 1024 1024
> 1024 1024), I get 0.
> (* 1024 1024) works correctly, but repeating '1024' more than two times
> gives wrong value.

A 32-bit build of Emacs cannot correctly do integer math beyond the
value of most-positive-fixnum, whose value is 536870911.  This is a
fundamental limitation of Emacs Lisp, not a bug.

You can work around this bu using floating-point numbers:

  (* 1024.0 1024.0 1024.0) => 1073741824.0

Closing.

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