exp2l: Work around a NetBSD 10.0/i386 bug

[Bruno Haible]

On NetBSD 10.0/i386, I see this test failure:

FAIL: test-exp2l
================

../../gltests/test-exp2.h:50: assertion 'z == y' failed
FAIL test-exp2l (exit status: 134)

The cause is that exp2l(x) is Infinity already for x = 1024.
Although LDBL_MAX_EXP is 16384.

This patch activates a gnulib override.


2024-04-05  Bruno Haible  <bruno@clisp.org>

        exp2l: Work around a NetBSD 10.0/i386 bug.
        * m4/exp2l.m4 (gl_FUNC_EXP2L): Test the value of exp2l(LDBL_MAX_EXP-1).
        * doc/posix-functions/exp2l.texi: Mention the NetBSD 10.0/i386 bug.

diff --git a/doc/posix-functions/exp2l.texi b/doc/posix-functions/exp2l.texi
index 777182ec51..5de6d47469 100644
--- a/doc/posix-functions/exp2l.texi
+++ b/doc/posix-functions/exp2l.texi
@@ -15,9 +15,12 @@
 This function is not declared on some platforms:
 IRIX 6.5.
 @item
+This function returns Infinity instead of large finite values on some 
platforms:
+NetBSD 10.0/i386.
+@item
 This function produces results which are accurate to only 16 digits on some
 platforms:
-NetBSD 10.0.
+NetBSD 10.0/x86_64.
 @end itemize
 
 Portability problems fixed by Gnulib module @code{exp2l-ieee}:
diff --git a/m4/exp2l.m4 b/m4/exp2l.m4
index 2dd134740c..7de6f8de4b 100644
--- a/m4/exp2l.m4
+++ b/m4/exp2l.m4
@@ -1,5 +1,5 @@
 # exp2l.m4
-# serial 14
+# serial 15
 dnl Copyright (C) 2010-2024 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -81,7 +81,7 @@ AC_DEFUN([gl_FUNC_EXP2L]
 {
   long double (* volatile my_exp2l) (long double) = argc ? exp2l : dummy;
   int result = 0;
-  /* This test fails on NetBSD 9.3.  */
+  /* This test fails on NetBSD 10.0/x86_64.  */
   {
     const long double TWO_LDBL_MANT_DIG = /* 2^LDBL_MANT_DIG */
       (long double) (1U << ((LDBL_MANT_DIG - 1) / 5))
@@ -94,6 +94,13 @@ AC_DEFUN([gl_FUNC_EXP2L]
     if (!(err >= -100.0L && err <= 100.0L))
       result |= 1;
   }
+  /* This test fails on NetBSD 10.0/i386.  */
+  {
+    long double x = LDBL_MAX_EXP - 1;
+    long double z = my_exp2l (x);
+    if (z + z == z) /* isinf (z) */
+      result |= 2;
+  }
   return result;
 }
             ]])],