expm1f-ieee: Work around AIX 7.2 bug

[Bruno Haible]

On AIX 7.2 I see a test failure:

FAIL: test-expm1f-ieee
======================

../../gltests/test-expm1-ieee.h:37: assertion '!!signbit (z) == !!signbit 
(MINUS_ZERO)' failed
FAIL test-expm1f-ieee (exit status: 134)

The cause is that expm1f (-0.0f) return +0.0f instead of -0.0f.
This patch fixes it.


2021-01-04  Bruno Haible  <bruno@clisp.org>

        expm1f-ieee: Work around AIX 7.2 bug.
        * m4/expm1f.m4 (gl_FUNC_EXPM1F): Initialize gl_expm1f_required. If
        module 'expm1f-ieee' is in use, check whether expm1f works according to
        IEEE.
        * m4/expm1f-ieee.m4: New file.
        * modules/expm1f-ieee (Files): Add it.
        (Depends-on): Update conditions.
        (configure.ac): Invoke gl_FUNC_EXPM1F_IEEE.
        * doc/posix-functions/expm1f.texi: Mention the AIX bug.

diff --git a/doc/posix-functions/expm1f.texi b/doc/posix-functions/expm1f.texi
index c732cfe..e95e510 100644
--- a/doc/posix-functions/expm1f.texi
+++ b/doc/posix-functions/expm1f.texi
@@ -4,9 +4,9 @@
 
 POSIX specification:@* 
@url{https://pubs.opengroup.org/onlinepubs/9699919799/functions/expm1f.html}
 
-Gnulib module: expm1f
+Gnulib module: expm1f or expm1f-ieee
 
-Portability problems fixed by Gnulib:
+Portability problems fixed by either Gnulib module @code{expm1f} or 
@code{expm1f-ieee}:
 @itemize
 @item
 This function is missing on some platforms:
@@ -16,6 +16,14 @@ This function produces wrong results for arguments <= 
@minus{}17.32868 on some p
 IRIX 6.5.
 @end itemize
 
+Portability problems fixed by Gnulib module @code{expm1f-ieee}:
+@itemize
+@item
+This function returns a positive zero for a minus zero argument
+on some platforms:
+AIX 7.2.
+@end itemize
+
 Portability problems not fixed by Gnulib:
 @itemize
 @end itemize
diff --git a/m4/expm1f-ieee.m4 b/m4/expm1f-ieee.m4
new file mode 100644
index 0000000..5344955
--- /dev/null
+++ b/m4/expm1f-ieee.m4
@@ -0,0 +1,15 @@
+# expm1f-ieee.m4 serial 1
+dnl Copyright (C) 2021 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.
+
+dnl This macro is in a separate file (not in expm1f.m4 and not inlined in the
+dnl module description), so that gl_FUNC_EXPM1F can test whether 'aclocal' has
+dnl found uses of this macro.
+
+AC_DEFUN([gl_FUNC_EXPM1F_IEEE],
+[
+  m4_divert_text([INIT_PREPARE], [gl_expm1f_required=ieee])
+  AC_REQUIRE([gl_FUNC_EXPM1F])
+])
diff --git a/m4/expm1f.m4 b/m4/expm1f.m4
index 5cb661f..c18ff1a 100644
--- a/m4/expm1f.m4
+++ b/m4/expm1f.m4
@@ -1,4 +1,4 @@
-# expm1f.m4 serial 3
+# expm1f.m4 serial 4
 dnl Copyright (C) 2011-2021 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -6,6 +6,7 @@ dnl with or without modifications, as long as this notice is 
preserved.
 
 AC_DEFUN([gl_FUNC_EXPM1F],
 [
+  m4_divert_text([DEFAULTS], [gl_expm1f_required=plain])
   AC_REQUIRE([gl_MATH_H_DEFAULTS])
   AC_REQUIRE([gl_FUNC_EXPM1])
 
@@ -20,6 +21,7 @@ AC_DEFUN([gl_FUNC_EXPM1F],
   LIBS="$save_LIBS"
   if test $ac_cv_func_expm1f = yes; then
     EXPM1F_LIBM="$EXPM1_LIBM"
+
     save_LIBS="$LIBS"
     LIBS="$LIBS $EXPM1F_LIBM"
     gl_FUNC_EXPM1F_WORKS
@@ -28,6 +30,73 @@ AC_DEFUN([gl_FUNC_EXPM1F],
       *yes) ;;
       *) REPLACE_EXPM1F=1 ;;
     esac
+
+    m4_ifdef([gl_FUNC_EXPM1F_IEEE], [
+      if test $gl_expm1f_required = ieee && test $REPLACE_EXPM1F = 0; then
+        AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+        AC_CACHE_CHECK([whether expm1f works according to ISO C 99 with IEC 
60559],
+          [gl_cv_func_expm1f_ieee],
+          [
+            save_LIBS="$LIBS"
+            LIBS="$LIBS $EXPM1F_LIBM"
+            AC_RUN_IFELSE(
+              [AC_LANG_SOURCE([[
+#ifndef __NO_MATH_INLINES
+# define __NO_MATH_INLINES 1 /* for glibc */
+#endif
+#include <math.h>
+]gl_FLOAT_MINUS_ZERO_CODE[
+]gl_FLOAT_SIGNBIT_CODE[
+#ifndef expm1f
+extern
+#ifdef __cplusplus
+"C"
+#endif
+float expm1f (float);
+#endif
+/* Compare two numbers with ==.
+   This is a separate function because IRIX 6.5 "cc -O" miscompiles an
+   'x == x' test.  */
+static int
+numeric_equal (float x, float y)
+{
+  return x == y;
+}
+static float dummy (float x) { return 0; }
+int main (int argc, char *argv[])
+{
+  float (* volatile my_expm1f) (float) = argc ? expm1f : dummy;
+  /* Test expm1f(-0.0f).
+     This test fails on AIX 7.2.  */
+  float y = my_expm1f (minus_zerof);
+  if (signbitf (minus_zerof) && !signbitf (y))
+    return 1;
+  return 0;
+}
+              ]])],
+              [gl_cv_func_expm1f_ieee=yes],
+              [gl_cv_func_expm1f_ieee=no],
+              [case "$host_os" in
+                                # Guess yes on glibc systems.
+                 *-gnu* | gnu*) gl_cv_func_expm1f_ieee="guessing yes" ;;
+                                # Guess yes on musl systems.
+                 *-musl*)       gl_cv_func_expm1f_ieee="guessing yes" ;;
+                                # Guess yes on native Windows.
+                 mingw*)        gl_cv_func_expm1f_ieee="guessing yes" ;;
+                                # Guess no on AIX.
+                 aix*)          gl_cv_func_expm1f_ieee="guessing no" ;;
+                                # If we don't know, obey 
--enable-cross-guesses.
+                 *)             
gl_cv_func_expm1f_ieee="$gl_cross_guess_normal" ;;
+               esac
+              ])
+            LIBS="$save_LIBS"
+          ])
+        case "$gl_cv_func_expm1f_ieee" in
+          *yes) ;;
+          *) REPLACE_EXPM1F=1 ;;
+        esac
+      fi
+    ])
   else
     HAVE_EXPM1F=0
   fi
diff --git a/modules/expm1f-ieee b/modules/expm1f-ieee
index ed966e0..ffab1d7 100644
--- a/modules/expm1f-ieee
+++ b/modules/expm1f-ieee
@@ -2,14 +2,15 @@ Description:
 expm1f() function according to ISO C 99 with IEC 60559.
 
 Files:
+m4/expm1f-ieee.m4
 
 Depends-on:
 expm1f
 fpieee
-expm1-ieee      [test $HAVE_EXPM1F = 0]
+expm1-ieee      [test $HAVE_EXPM1F = 0 || test $REPLACE_EXPM1F = 1]
 
 configure.ac:
-AC_REQUIRE([gl_FUNC_EXPM1F])
+gl_FUNC_EXPM1F_IEEE
 
 Makefile.am: