bug#13419: make 'eabs' act more like a function

[Paul Eggert <eggert@cs.ucla.edu>]

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On 01/12/2013 05:25 AM, Stefan Monnier wrote:
> Do you really consider this code cleaner?

The implementation's worse, but the use is nicer,
since eabs is guaranteed to evaluate its argument just once.

Anyway, here's a simpler implementation that also evaluates
its argument just once: would you prefer this?

  #define eabs(x) imaxabs (x)

(This is shorter and simpler than what's in Emacs now.)

I've attached a complete patch based on this idea.
It incorporates Eli's suggestion to implement imaxabs
via abs rather than labs on 32-bit MS-Windows.  (The
idea is to avoid the need to build imaxabs.o on Windows.)

[-- Attachment #2: eabs-imaxabs.txt --]
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=== modified file 'ChangeLog'
--- ChangeLog	2013-01-12 05:21:06 +0000
+++ ChangeLog	2013-01-12 23:02:00 +0000
@@ -1,5 +1,9 @@
 2013-01-12  Paul Eggert  <eggert@cs.ucla.edu>
 
+	Make eabs act more like a function.
+	* lib/imaxabs.c, m4/imaxabs.m4: New files, from gnulib.
+	* lib/gnulib.mk, m4/gnulib-comp.m4: Regenerate.
+
 	Enable conservative stack scanning for all architectures.
 	Suggested by Stefan Monnier in
 	<http://lists.gnu.org/archive/html/emacs-devel/2013-01/msg00183.html>.

=== modified file 'admin/ChangeLog'
--- admin/ChangeLog	2013-01-10 03:43:02 +0000
+++ admin/ChangeLog	2013-01-12 23:02:00 +0000
@@ -1,3 +1,8 @@
+2013-01-12  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Make eabs act more like a function.
+	* merge-gnulib (GNULIB_MODULES): Add imaxabs.
+
 2013-01-03  Glenn Morris  <rgm@gnu.org>
 
 	* check-doc-strings: Update for CVS->bzr, moved lispref/ directory.

=== modified file 'admin/merge-gnulib'
--- admin/merge-gnulib	2013-01-02 16:13:04 +0000
+++ admin/merge-gnulib	2013-01-12 23:02:00 +0000
@@ -30,7 +30,7 @@
   careadlinkat close-stream crypto/md5 crypto/sha1 crypto/sha256 crypto/sha512
   dtoastr dtotimespec dup2 environ execinfo faccessat
   fcntl-h filemode getloadavg getopt-gnu gettime gettimeofday
-  ignore-value intprops largefile lstat
+  ignore-value imaxabs intprops largefile lstat
   manywarnings mktime pselect pthread_sigmask putenv readlink
   sig2str socklen stat-time stdalign stdarg stdbool stdio
   strftime strtoimax strtoumax symlink sys_stat

=== modified file 'lib/gnulib.mk'
--- lib/gnulib.mk	2013-01-04 02:17:49 +0000
+++ lib/gnulib.mk	2013-01-12 23:02:00 +0000
@@ -21,7 +21,7 @@
 # the same distribution terms as the rest of that program.
 #
 # Generated by gnulib-tool.
-# Reproduce by: gnulib-tool --import --dir=. --lib=libgnu --source-base=lib --m4-base=m4 --doc-base=doc --tests-base=tests --aux-dir=build-aux --avoid=at-internal --avoid=errno --avoid=fchdir --avoid=fcntl --avoid=fstat --avoid=malloc-posix --avoid=msvc-inval --avoid=msvc-nothrow --avoid=openat-die --avoid=openat-h --avoid=raise --avoid=save-cwd --avoid=select --avoid=sigprocmask --avoid=sys_types --avoid=threadlib --makefile-name=gnulib.mk --conditional-dependencies --no-libtool --macro-prefix=gl --no-vc-files alloca-opt c-ctype c-strcase careadlinkat close-stream crypto/md5 crypto/sha1 crypto/sha256 crypto/sha512 dtoastr dtotimespec dup2 environ execinfo faccessat fcntl-h filemode getloadavg getopt-gnu gettime gettimeofday ignore-value intprops largefile lstat manywarnings mktime pselect pthread_sigmask putenv readlink sig2str socklen stat-time stdalign stdarg stdbool stdio strftime strtoimax strtoumax symlink sys_stat sys_time time timer-time timespec-add timespec-sub unsetenv utimens warnings
+# Reproduce by: gnulib-tool --import --dir=. --lib=libgnu --source-base=lib --m4-base=m4 --doc-base=doc --tests-base=tests --aux-dir=build-aux --avoid=at-internal --avoid=errno --avoid=fchdir --avoid=fcntl --avoid=fstat --avoid=malloc-posix --avoid=msvc-inval --avoid=msvc-nothrow --avoid=openat-die --avoid=openat-h --avoid=raise --avoid=save-cwd --avoid=select --avoid=sigprocmask --avoid=sys_types --avoid=threadlib --makefile-name=gnulib.mk --conditional-dependencies --no-libtool --macro-prefix=gl --no-vc-files alloca-opt c-ctype c-strcase careadlinkat close-stream crypto/md5 crypto/sha1 crypto/sha256 crypto/sha512 dtoastr dtotimespec dup2 environ execinfo faccessat fcntl-h filemode getloadavg getopt-gnu gettime gettimeofday ignore-value imaxabs intprops largefile lstat manywarnings mktime pselect pthread_sigmask putenv readlink sig2str socklen stat-time stdalign stdarg stdbool stdio strftime strtoimax strtoumax symlink sys_stat sys_time time timer-time timespec-add timespec-sub unsetenv utimens warnings
 
 
 MOSTLYCLEANFILES += core *.stackdump
@@ -343,6 +343,15 @@
 
 ## end   gnulib module ignore-value
 
+## begin gnulib module imaxabs
+
+
+EXTRA_DIST += imaxabs.c
+
+EXTRA_libgnu_a_SOURCES += imaxabs.c
+
+## end   gnulib module imaxabs
+
 ## begin gnulib module intprops
 
 

=== added file 'lib/imaxabs.c'
--- lib/imaxabs.c	1970-01-01 00:00:00 +0000
+++ lib/imaxabs.c	2013-01-12 23:02:00 +0000
@@ -0,0 +1,26 @@
+/* imaxabs() function: absolute value of 'intmax_t'.
+   Copyright (C) 2006, 2009-2013 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <inttypes.h>
+
+intmax_t
+imaxabs (intmax_t x)
+{
+  return (x >= 0 ? x : - x);
+}

=== modified file 'm4/gnulib-comp.m4'
--- m4/gnulib-comp.m4	2013-01-04 02:17:49 +0000
+++ m4/gnulib-comp.m4	2013-01-12 23:02:00 +0000
@@ -72,6 +72,7 @@
   # Code from module gettimeofday:
   # Code from module group-member:
   # Code from module ignore-value:
+  # Code from module imaxabs:
   # Code from module include_next:
   # Code from module intprops:
   # Code from module inttypes-incomplete:
@@ -216,6 +217,12 @@
     gl_PREREQ_GETTIMEOFDAY
   fi
   gl_SYS_TIME_MODULE_INDICATOR([gettimeofday])
+  gl_FUNC_IMAXABS
+  if test $ac_cv_func_imaxabs = no; then
+    AC_LIBOBJ([imaxabs])
+    gl_PREREQ_IMAXABS
+  fi
+  gl_INTTYPES_MODULE_INDICATOR([imaxabs])
   gl_INTTYPES_INCOMPLETE
   AC_REQUIRE([gl_LARGEFILE])
   gl_FUNC_LSTAT
@@ -682,6 +689,7 @@
   lib/gettimeofday.c
   lib/group-member.c
   lib/ignore-value.h
+  lib/imaxabs.c
   lib/intprops.h
   lib/inttypes.in.h
   lib/lstat.c
@@ -764,6 +772,7 @@
   m4/gettimeofday.m4
   m4/gnulib-common.m4
   m4/group-member.m4
+  m4/imaxabs.m4
   m4/include_next.m4
   m4/inttypes.m4
   m4/largefile.m4

=== added file 'm4/imaxabs.m4'
--- m4/imaxabs.m4	1970-01-01 00:00:00 +0000
+++ m4/imaxabs.m4	2013-01-12 23:02:00 +0000
@@ -0,0 +1,20 @@
+# imaxabs.m4 serial 4
+dnl Copyright (C) 2006, 2009-2013 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_FUNC_IMAXABS],
+[
+  AC_REQUIRE([gl_INTTYPES_H_DEFAULTS])
+
+  dnl On OSF/1 5.1 with cc, this function is declared but not defined.
+  AC_CHECK_FUNCS_ONCE([imaxabs])
+  AC_CHECK_DECLS_ONCE([imaxabs])
+  if test "$ac_cv_have_decl_imaxabs" != yes; then
+    HAVE_DECL_IMAXABS=0
+  fi
+])
+
+# Prerequisites of lib/imaxabs.c.
+AC_DEFUN([gl_PREREQ_IMAXABS], [:])

=== modified file 'nt/ChangeLog'
--- nt/ChangeLog	2013-01-11 09:33:54 +0000
+++ nt/ChangeLog	2013-01-12 23:02:00 +0000
@@ -1,3 +1,8 @@
+2013-01-12  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Make eabs act more like a function.
+	* inc/inttypes.h (imaxabs) [!__MINGW32__]: New macro.
+
 2013-01-11  Eli Zaretskii  <eliz@gnu.org>
 
 	* inc/unistd.h (O_IGNORE_CTTY): Define, as it is unconditionally

=== modified file 'nt/inc/inttypes.h'
--- nt/inc/inttypes.h	2013-01-01 09:11:05 +0000
+++ nt/inc/inttypes.h	2013-01-12 23:02:00 +0000
@@ -25,9 +25,11 @@
 #else  /* !__MINGW32__ */
 #include "stdint.h"
 #ifdef _WIN64
+#define imaxabs _abs64
 #define strtoumax _strtoui64
 #define strtoimax _strtoi64
 #else
+#define imaxabs abs
 #define strtoumax strtoul
 #define strtoimax strtol
 #endif

=== modified file 'src/ChangeLog'
--- src/ChangeLog	2013-01-12 06:15:12 +0000
+++ src/ChangeLog	2013-01-12 23:02:00 +0000
@@ -1,3 +1,8 @@
+2013-01-12  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Make eabs act more like a function.
+	* lisp.h (eabs): Evaluate arg just once.
+
 2013-01-12  Dmitry Antipov  <dmantipov@yandex.ru>
 
 	* indent.c (Fvertical_motion): Remove now-incorrect GCPROs

=== modified file 'src/lisp.h'
--- src/lisp.h	2013-01-12 05:21:06 +0000
+++ src/lisp.h	2013-01-12 23:02:00 +0000
@@ -3626,12 +3626,10 @@
 /* Set up the name of the machine we're running on.  */
 extern void init_system_name (void);
 
-/* We used to use `abs', but that clashes with system headers on some
-   platforms, and using a name reserved by Standard C is a bad idea
-   anyway.  */
-#if !defined (eabs)
-#define eabs(x)         ((x) < 0 ? -(x) : (x))
-#endif
+/* Return the absolute value of X, without evaluating X more than once.
+   X should be a signed integer, and X's absolute value should not
+   exceed the maximum for its promoted type.  */
+#define eabs(x) imaxabs (x)
 
 /* Return a fixnum or float, depending on whether VAL fits in a Lisp
    fixnum.  */