Re: module for missing math.h functions?

[Ben Pfaff]

Paul Eggert <address@hidden> writes:

> For other math.h functions it's a vital question, but you should be
> able to implement trunc and round portably using ceil and floor, and
> this should work correctly even for IEEE 754 hosts.  Something like
> this:
>
>    double
>    rpl_trunc (double x)
>    {
>      return x < 0 ? ceil (x) : 0 < x ? floor (x) : x;
>    }
>    [...]

You are cleverer than me.  Thanks.

Here is my first stab at a module.  I don't really know what I'm
doing--I just tried to look at modules that did similar things
for guidance, but it wasn't always clear to me which of several
choices to pick--so feedback is very much appreciated.

The following actually makes an unconditional wrapper around
<math.h>, in the same way as the fcntl module does.

I used floorl and ceill from the mathl module to implement roundl
and truncl.  I defined roundf and truncf to just call round and
trunc, but another option would be to implement floorf and ceilf
in the same way as roundl and truncl.

I haven't actually tested the function implementations.  It does
pass "gnulib-tool --test math" for what it's worth, at least on
my GNU/Linux system.

Index: MODULES.html.sh
===================================================================
RCS file: /cvsroot/gnulib/gnulib/MODULES.html.sh,v
retrieving revision 1.161
diff -u -p -r1.161 MODULES.html.sh
--- MODULES.html.sh     20 Nov 2006 22:07:27 -0000      1.161
+++ MODULES.html.sh     28 Nov 2006 06:08:45 -0000
@@ -1832,6 +1832,7 @@ func_all_modules ()
   func_echo "$element"
 
   func_begin_table
+  func_module math
   func_module mathl
   func_end_table
 
Index: lib/math_.h
===================================================================
RCS file: lib/math_.h
diff -N lib/math_.h
--- /dev/null   1 Jan 1970 00:00:00 -0000
+++ lib/math_.h 28 Nov 2006 06:08:45 -0000
@@ -0,0 +1,46 @@
+/* Provide a more complete set of math functions.
+   Copyright (C) 2006 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 2, 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, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+/* Written by Ben Pfaff.  */
+
+#ifndef _gl_MATH_H
+#define _gl_MATH_H
+
+#include @ABSOLUTE_MATH_H@
+#include "mathl.h"
+
+#if !HAVE_DECL_ROUNDF
+float roundf (float);
+#endif
+#if !HAVE_DECL_ROUND
+double round (double);
+#endif
+#if !HAVE_DECL_ROUNDL
+long double roundl (long double);
+#endif
+
+#if !HAVE_DECL_TRUNCF
+float truncf (float);
+#endif
+#if !HAVE_DECL_TRUNC
+double trunc (double);
+#endif
+#if !HAVE_DECL_TRUNCL
+long double truncl (long double);
+#endif
+
+#endif /* _gl_MATH_H */
Index: lib/round.c
===================================================================
RCS file: lib/round.c
diff -N lib/round.c
--- /dev/null   1 Jan 1970 00:00:00 -0000
+++ lib/round.c 28 Nov 2006 06:08:45 -0000
@@ -0,0 +1,75 @@
+/* round.c - portable implementation of round functions.
+
+   Copyright (C) 2006 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 2, 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, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+
+   Written by Paul Eggert and Ben Pfaff.  */
+
+#include <math.h>
+
+#if !HAVE_ROUNDF
+float
+roundf (float x)
+{
+  return round (x);
+}
+#endif /* !HAVE_ROUND */
+
+#if !HAVE_ROUND
+double
+round (double x)
+{
+  if (x < 0)
+    {
+      double t = ceil (x);
+      if (0.5 <= t - x)
+        t--;
+      return t;
+    }
+  else if (0 < x)
+    {
+      double t = floor (x);
+      if (0.5 <= x - t)
+        t++;
+      return t;  
+    }
+  else
+    return x;
+}
+#endif /* !HAVE_ROUND */
+
+#if !HAVE_ROUNDL
+long double
+roundl (long double x)
+{
+  if (x < 0)
+    {
+      long double t = ceill (x);
+      if (0.5 <= t - x)
+        t--;
+      return t;
+    }
+  else if (0 < x)
+    {
+      long double t = floorl (x);
+      if (0.5 <= x - t)
+        t++;
+      return t;  
+    }
+  else
+    return x;
+}
+#endif /* !HAVE_ROUNDL */
Index: lib/trunc.c
===================================================================
RCS file: lib/trunc.c
diff -N lib/trunc.c
--- /dev/null   1 Jan 1970 00:00:00 -0000
+++ lib/trunc.c 28 Nov 2006 06:08:45 -0000
@@ -0,0 +1,45 @@
+/* trunc.c - portable implementation of trunc functions.
+
+   Copyright (C) 2006 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 2, 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, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+
+   Written by Paul Eggert and Ben Pfaff.  */
+
+#include <math.h>
+
+#if !HAVE_TRUNCF
+float
+truncf (float x)
+{
+  return trunc (x);
+}
+#endif /* !HAVE_TRUNC */
+
+#if !HAVE_TRUNC
+double
+trunc (double x)
+{
+  return x < 0 ? ceil (x) : 0 < x ? floor (x) : x;
+}
+#endif /* !HAVE_TRUNC */
+
+#if !HAVE_TRUNCL
+long double
+truncl (long double x)
+{
+  return x < 0 ? ceill (x) : 0 < x ? floorl (x) : x;
+}
+#endif /* !HAVE_TRUNCL */
Index: m4/math.m4
===================================================================
RCS file: m4/math.m4
diff -N m4/math.m4
--- /dev/null   1 Jan 1970 00:00:00 -0000
+++ m4/math.m4  28 Nov 2006 06:08:45 -0000
@@ -0,0 +1,24 @@
+# math.m4 serial 1
+dnl Copyright (C) 2006 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_MATH_H],
+[
+  dnl Persuade glibc to declare C99 math functions.
+  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+
+  AC_CHECK_LIB(m, atan)
+
+  AC_CHECK_DECLS([roundf, round, roundl,
+                  truncf, trunc, truncl], , , [#include <math.h>])
+  AC_CHECK_FUNCS([roundf round roundl], , [AC_LIBOBJ(round)])
+  AC_CHECK_FUNCS([truncf trunc truncl], , [AC_LIBOBJ(trunc)])
+
+  gl_ABSOLUTE_HEADER([math.h])
+  ABSOLUTE_MATH_H=\"$gl_cv_absolute_math_h\"
+  AC_SUBST([ABSOLUTE_MATH_H])
+  MATH_H='math.h'
+  AC_SUBST([MATH_H])
+])
Index: modules/math
===================================================================
RCS file: modules/math
diff -N modules/math
--- /dev/null   1 Jan 1970 00:00:00 -0000
+++ modules/math        28 Nov 2006 06:08:46 -0000
@@ -0,0 +1,39 @@
+Description:
+C99 functions for rounding floating-point numbers.
+
+Files:
+lib/math_.h
+lib/round.c
+lib/trunc.c
+m4/absolute-header.m4
+m4/math.m4
+
+Depends-on:
+extensions
+mathl
+
+configure.ac:
+gl_MATH_H
+
+Makefile.am:
+BUILT_SOURCES += $(MATH_H)
+
+# Create a wrapper around <math.h> that declares any missing C99
+# functions.
+math.h: math_.h
+       rm -f address@hidden $@
+       { echo '/* DO NOT EDIT! GENERATED AUTOMATICALLY! */'; \
+         sed -e 's|@''ABSOLUTE_MATH_H''@|$(ABSOLUTE_MATH_H)|g' \
+             < $(srcdir)/math_.h; \
+       } > address@hidden
+       mv address@hidden $@
+MOSTLYCLEANFILES += math.h math.h-t
+
+Include:
+#include <math.h>
+
+License:
+GPL
+
+Maintainer:
+Ben Pfaff <address@hidden>

-- 
Ben Pfaff 
email: address@hidden
web: http://benpfaff.org