--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,17 @@
+2012-03-08  Bruno Haible  <bruno@clisp.org>
+
+	New module 'exp2f'.
+	* lib/math.in.h (exp2f): New declaration.
+	* lib/exp2f.c: New file.
+	* m4/exp2f.m4: New file.
+	* m4/math_h.m4 (gl_MATH_H): Test whether exp2f is declared.
+	(gl_MATH_H_DEFAULTS): Initialize GNULIB_EXP2F, HAVE_DECL_EXP2F.
+	* modules/math (Makefile.am): Substitute GNULIB_EXP2F, HAVE_DECL_EXP2F.
+	* modules/exp2f: New file.
+	* tests/test-math-c++.cc: Check the declaration of exp2f.
+	* doc/posix-functions/exp2f.texi: Mention the new module and the
+	IRIX problem.
+
 2012-03-08  Bruno Haible  <bruno@clisp.org>
 
 	Tests for module 'exp2'.

--- a/doc/posix-functions/exp2f.texi
+++ b/doc/posix-functions/exp2f.texi
@@ -4,15 +4,18 @@
 
 POSIX specification:@* @url{http://www.opengroup.org/onlinepubs/9699919799/functions/exp2f.html}
 
-Gnulib module: ---
+Gnulib module: exp2f
 
 Portability problems fixed by Gnulib:
 @itemize
+@item
+This function is missing on some platforms:
+FreeBSD 5.2.1, NetBSD 5.0, OpenBSD 3.8, Minix 3.1.8, AIX 5.1, HP-UX 11, older IRIX 6.5, OSF/1 4.0, Solaris 9, MSVC 9, Interix 3.5.
+@item
+This function is not declared on some platforms:
+IRIX 6.5.
 @end itemize
 
 Portability problems not fixed by Gnulib:
 @itemize
-@item
-This function is missing on some platforms:
-FreeBSD 5.2.1, NetBSD 5.0, OpenBSD 3.8, Minix 3.1.8, AIX 5.1, HP-UX 11, IRIX 6.5, OSF/1 4.0, Solaris 9, MSVC 9, Interix 3.5.
 @end itemize

new file mode 100644
--- /dev/null
+++ b/lib/exp2f.c
@@ -0,0 +1,26 @@
+/* Exponential base 2 function.
+   Copyright (C) 2011-2012 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 <math.h>
+
+float
+exp2f (float x)
+{
+  return (float) exp2 ((double) x);
+}

--- a/lib/math.in.h
+++ b/lib/math.in.h
@@ -532,6 +532,20 @@
 #endif
 
 
+#if @GNULIB_EXP2F@
+# if !@HAVE_DECL_EXP2F@
+_GL_FUNCDECL_SYS (exp2f, float, (float x));
+# endif
+_GL_CXXALIAS_SYS (exp2f, float, (float x));
+_GL_CXXALIASWARN (exp2f);
+#elif defined GNULIB_POSIXCHECK
+# undef exp2f
+# if HAVE_RAW_DECL_EXP2F
+_GL_WARN_ON_USE (exp2f, "exp2f is unportable - "
+                 "use gnulib module exp2f for portability");
+# endif
+#endif
+
 #if @GNULIB_EXP2@
 # if @REPLACE_EXP2@
 #  if !(defined __cplusplus && defined GNULIB_NAMESPACE)

new file mode 100644
--- /dev/null
+++ b/m4/exp2f.m4
@@ -0,0 +1,34 @@
+# exp2f.m4 serial 1
+dnl Copyright (C) 2011-2012 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_EXP2F],
+[
+  AC_REQUIRE([gl_MATH_H_DEFAULTS])
+  AC_REQUIRE([gl_FUNC_EXP2])
+
+  dnl Persuade glibc <math.h> to declare exp2f().
+  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+
+  dnl Test whether exp2f() exists. Assume that exp2f(), if it exists, is
+  dnl defined in the same library as exp2().
+  save_LIBS="$LIBS"
+  LIBS="$LIBS $EXP2_LIBM"
+  AC_CHECK_FUNCS([exp2f])
+  LIBS="$save_LIBS"
+  if test $ac_cv_func_exp2f = yes; then
+    HAVE_EXP2F=1
+    EXP2F_LIBM="$EXP2_LIBM"
+    dnl Also check whether it's declared.
+    dnl IRIX 6.5 has exp2f() in libm but doesn't declare it in <math.h>.
+    AC_CHECK_DECL([exp2f], , [HAVE_DECL_EXP2F=0], [[#include <math.h>]])
+  else
+    HAVE_EXP2F=0
+    HAVE_DECL_EXP2F=0
+    dnl Find libraries needed to link lib/exp2f.c.
+    EXP2F_LIBM="$EXP2_LIBM"
+  fi
+  AC_SUBST([EXP2F_LIBM])
+])

--- a/m4/math_h.m4
+++ b/m4/math_h.m4
@@ -1,4 +1,4 @@
-# math_h.m4 serial 89
+# math_h.m4 serial 90
 dnl Copyright (C) 2007-2012 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -41,7 +41,8 @@
   gl_WARN_ON_USE_PREPARE([[#include <math.h>]],
     [acosf acosl asinf asinl atanf atanl
      cbrt cbrtf cbrtl ceilf ceill copysign copysignf copysignl cosf cosl coshf
-     expf expl exp2 expm1 expm1f expm1l fabsf fabsl floorf floorl fma fmaf fmal
+     expf expl exp2 exp2f expm1 expm1f expm1l
+     fabsf fabsl floorf floorl fma fmaf fmal
      fmod fmodf fmodl frexpf frexpl hypotf hypotl
      ldexpf ldexpl logb logf logl log10f log10l modf modff modfl powf
      remainder remainderf remainderl
@@ -82,6 +83,7 @@
   GNULIB_EXPF=0;       AC_SUBST([GNULIB_EXPF])
   GNULIB_EXPL=0;       AC_SUBST([GNULIB_EXPL])
   GNULIB_EXP2=0;       AC_SUBST([GNULIB_EXP2])
+  GNULIB_EXP2F=0;      AC_SUBST([GNULIB_EXP2F])
   GNULIB_EXPM1=0;      AC_SUBST([GNULIB_EXPM1])
   GNULIB_EXPM1F=0;     AC_SUBST([GNULIB_EXPM1F])
   GNULIB_EXPM1L=0;     AC_SUBST([GNULIB_EXPM1L])
@@ -204,6 +206,7 @@
   HAVE_DECL_COSL=1;            AC_SUBST([HAVE_DECL_COSL])
   HAVE_DECL_EXPL=1;            AC_SUBST([HAVE_DECL_EXPL])
   HAVE_DECL_EXP2=1;            AC_SUBST([HAVE_DECL_EXP2])
+  HAVE_DECL_EXP2F=1;           AC_SUBST([HAVE_DECL_EXP2F])
   HAVE_DECL_EXPM1L=1;          AC_SUBST([HAVE_DECL_EXPM1L])
   HAVE_DECL_FLOORF=1;          AC_SUBST([HAVE_DECL_FLOORF])
   HAVE_DECL_FLOORL=1;          AC_SUBST([HAVE_DECL_FLOORL])

new file mode 100644
--- /dev/null
+++ b/modules/exp2f
@@ -0,0 +1,32 @@
+Description:
+exp2f() function: exponential base 2 function.
+
+Files:
+lib/exp2f.c
+m4/exp2f.m4
+
+Depends-on:
+math
+extensions
+exp2            [test $HAVE_EXP2F = 0]
+
+configure.ac:
+gl_FUNC_EXP2F
+if test $HAVE_EXP2F = 0; then
+  AC_LIBOBJ([exp2f])
+fi
+gl_MATH_MODULE_INDICATOR([exp2f])
+
+Makefile.am:
+
+Include:
+<math.h>
+
+Link:
+$(EXP2F_LIBM)
+
+License:
+LGPL
+
+Maintainer:
+Bruno Haible

--- a/modules/math
+++ b/modules/math
@@ -50,6 +50,7 @@
 	      -e 's/@''GNULIB_EXPF''@/$(GNULIB_EXPF)/g' \
 	      -e 's/@''GNULIB_EXPL''@/$(GNULIB_EXPL)/g' \
 	      -e 's/@''GNULIB_EXP2''@/$(GNULIB_EXP2)/g' \
+	      -e 's/@''GNULIB_EXP2F''@/$(GNULIB_EXP2F)/g' \
 	      -e 's/@''GNULIB_EXPM1''@/$(GNULIB_EXPM1)/g' \
 	      -e 's/@''GNULIB_EXPM1F''@/$(GNULIB_EXPM1F)/g' \
 	      -e 's/@''GNULIB_EXPM1L''@/$(GNULIB_EXPM1L)/g' \
@@ -172,6 +173,7 @@
 	      -e 's|@''HAVE_DECL_COSL''@|$(HAVE_DECL_COSL)|g' \
 	      -e 's|@''HAVE_DECL_EXPL''@|$(HAVE_DECL_EXPL)|g' \
 	      -e 's|@''HAVE_DECL_EXP2''@|$(HAVE_DECL_EXP2)|g' \
+	      -e 's|@''HAVE_DECL_EXP2F''@|$(HAVE_DECL_EXP2F)|g' \
 	      -e 's|@''HAVE_DECL_EXPM1L''@|$(HAVE_DECL_EXPM1L)|g' \
 	      -e 's|@''HAVE_DECL_FLOORF''@|$(HAVE_DECL_FLOORF)|g' \
 	      -e 's|@''HAVE_DECL_FLOORL''@|$(HAVE_DECL_FLOORL)|g' \

--- a/tests/test-math-c++.cc
+++ b/tests/test-math-c++.cc
@@ -124,6 +124,9 @@
 SIGNATURE_CHECK (GNULIB_NAMESPACE::expl, long double, (long double));
 #endif
 
+#if GNULIB_TEST_EXP2F
+SIGNATURE_CHECK (GNULIB_NAMESPACE::exp2f, float, (float));
+#endif
 #if GNULIB_TEST_EXP2
 SIGNATURE_CHECK (GNULIB_NAMESPACE::exp2, double, (double));
 #endif