[PATCH, libstdc++] PR libstdc++/68397 std::tr1::expint fails ... long double arguments.

[Ed Smith-Rowland]

Here is a patch for

   PR libstdc++/68397 std::tr1::expint fails in __expint_En_cont_frac 
for some long double arguments due to low __max_iter value.

The proposed resolution of increasing the max_iter to 1000 is a simple 
and obvious fix.

Built and tested on x86_64-linux.

OK?

Ed


-------------- next part --------------
2017-04-20  Edward Smith-Rowland  <3dw4rd@verizon.net>

	PR libstdc++/68397 std::tr1::expint fails ... long double arguments.
	* include/tr1/exp_integral.tcc: Increase iteration limits.
	* testsuite/tr1/5_numerical_facilities/special_functions/15_expint/
	pr68397.cc: New test.
	* testsuite/special_functions/14_expint/pr68397.cc: New test.
-------------- next part --------------
Index: include/tr1/exp_integral.tcc
===================================================================
--- include/tr1/exp_integral.tcc	(revision 246797)
+++ include/tr1/exp_integral.tcc	(working copy)
@@ -86,7 +86,7 @@
       _Tp __term = _Tp(1);
       _Tp __esum = _Tp(0);
       _Tp __osum = _Tp(0);
-      const unsigned int __max_iter = 100;
+      const unsigned int __max_iter = 1000;
       for (unsigned int __i = 1; __i < __max_iter; ++__i)
         {
           __term *= - __x / __i;
@@ -156,7 +156,7 @@
     _Tp
     __expint_En_series(unsigned int __n, _Tp __x)
     {
-      const unsigned int __max_iter = 100;
+      const unsigned int __max_iter = 1000;
       const _Tp __eps = std::numeric_limits<_Tp>::epsilon();
       const int __nm1 = __n - 1;
       _Tp __ans = (__nm1 != 0
@@ -202,7 +202,7 @@
     _Tp
     __expint_En_cont_frac(unsigned int __n, _Tp __x)
     {
-      const unsigned int __max_iter = 100;
+      const unsigned int __max_iter = 1000;
       const _Tp __eps = std::numeric_limits<_Tp>::epsilon();
       const _Tp __fp_min = std::numeric_limits<_Tp>::min();
       const int __nm1 = __n - 1;
Index: testsuite/tr1/5_numerical_facilities/special_functions/15_expint/pr68397.cc
===================================================================
--- testsuite/tr1/5_numerical_facilities/special_functions/15_expint/pr68397.cc	(nonexistent)
+++ testsuite/tr1/5_numerical_facilities/special_functions/15_expint/pr68397.cc	(working copy)
@@ -0,0 +1,46 @@
+// Copyright (C) 2017 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library 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, or (at your option)
+// any later version.
+//
+// This library 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 library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// PR libstdc++/68397 -  std::tr1::expint fails in __expint_En_cont_frac
+// for some long double arguments due to low __max_iter value
+
+#include <tr1/cmath>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  // Answers from Wolfram Alpha.
+  long double ans_ok = -0.10001943365331651406888645149537315243646135979573L;
+  long double ans_bomb = -0.10777727809650077516264612749163100483995270163783L;
+
+  long double Ei_ok = std::tr1::expint(-1.500001L);
+  long double diff_ok = std::abs(Ei_ok - ans_ok);
+  VERIFY(diff_ok < 1.0e-15L);
+
+  long double Ei_bomb = std::tr1::expint(-1.450001L);
+  long double diff_bomb = std::abs(Ei_bomb - ans_bomb);
+  VERIFY(diff_bomb < 1.0e-15L);
+}
+
+int
+main()
+{
+  test01();
+  return 0;
+}
+
Index: testsuite/special_functions/14_expint/pr68397.cc
===================================================================
--- testsuite/special_functions/14_expint/pr68397.cc	(nonexistent)
+++ testsuite/special_functions/14_expint/pr68397.cc	(working copy)
@@ -0,0 +1,47 @@
+// { dg-do run { target c++11 } }
+// { dg-options "-D__STDCPP_WANT_MATH_SPEC_FUNCS__" }
+// Copyright (C) 2017 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library 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, or (at your option)
+// any later version.
+//
+// This library 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 library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// PR libstdc++/68397 -  std::tr1::expint fails in __expint_En_cont_frac
+// for some long double arguments due to low __max_iter value
+
+#include <cmath>
+#include <testsuite_hooks.h>
+
+int
+test01()
+{
+  // Answers from Wolfram Alpha.
+  long double ans_ok = -0.10001943365331651406888645149537315243646135979573L;
+  long double ans_bomb = -0.10777727809650077516264612749163100483995270163783L;
+
+  auto Ei_ok = std::expint(-1.500001L);
+  auto diff_ok = Ei_ok - ans_ok;
+  VERIFY(std::abs(diff_ok) < 1.0e-15);
+
+  auto Ei_bomb = std::expint(-1.450001L);
+  auto diff_bomb = Ei_bomb - ans_bomb;
+  VERIFY(std::abs(diff_bomb) < 1.0e-15);
+}
+
+int
+main()
+{
+  test01();
+  return 0;
+}