From e5b4f3f0c310a8396bc1fd5556c3662be012ca09 Mon Sep 17 00:00:00 2001
From: Matt Borland <matt@mattborland.com>
Date: Mon, 3 Apr 2023 14:50:22 +0200
Subject: [PATCH] Improve trunc handling

---
 .../boost/math/special_functions/round.hpp    |  1 +
 .../boost/math/special_functions/trunc.hpp    | 36 +++++++-
 test/git_issue_430.cpp                        | 92 +++++++++++++++++++
 3 files changed, 125 insertions(+), 4 deletions(-)

diff --git a/include/boost/math/special_functions/round.hpp b/include/boost/math/special_functions/round.hpp
index 454ee1a55..a1287d941 100644
--- a/include/boost/math/special_functions/round.hpp
+++ b/include/boost/math/special_functions/round.hpp
@@ -1,4 +1,5 @@
 //  Copyright John Maddock 2007.
+//  Copyright Matt Borland 2023.
 //  Use, modification and distribution are subject to the
 //  Boost Software License, Version 1.0. (See accompanying file
 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
diff --git a/include/boost/math/special_functions/trunc.hpp b/include/boost/math/special_functions/trunc.hpp
index d128d2c48..93a3f3056 100644
--- a/include/boost/math/special_functions/trunc.hpp
+++ b/include/boost/math/special_functions/trunc.hpp
@@ -1,4 +1,5 @@
 //  Copyright John Maddock 2007.
+//  Copyright Matt Borland 2023.
 //  Use, modification and distribution are subject to the
 //  Boost Software License, Version 1.0. (See accompanying file
 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
@@ -16,6 +17,13 @@
 #include <boost/math/policies/error_handling.hpp>
 #include <boost/math/special_functions/fpclassify.hpp>
 
+#if __cplusplus >= 201703L || _MSVC_LANG >= 201703L
+#include <boost/math/ccmath/ldexp.hpp>
+#  if !defined(BOOST_MATH_NO_CONSTEXPR_DETECTION) && !defined(TEST_GROUP_7) // Concept tests throw off constexpr ldexp
+#    define BOOST_MATH_HAS_CONSTEXPR_LDEXP
+#  endif
+#endif
+
 namespace boost{ namespace math{ namespace detail{
 
 template <class T, class Policy>
@@ -67,7 +75,14 @@ inline int itrunc(const T& v, const Policy& pol)
    BOOST_MATH_STD_USING
    using result_type = tools::promote_args_t<T>;
    result_type r = boost::math::trunc(v, pol);
-   if(r > static_cast<result_type>((std::numeric_limits<int>::max)()) || r < static_cast<result_type>((std::numeric_limits<int>::min)()))
+
+   #ifdef BOOST_MATH_HAS_CONSTEXPR_LDEXP
+   constexpr result_type max_val = boost::math::ccmath::ldexp(static_cast<result_type>(1), std::numeric_limits<int>::digits);
+   #else
+   static const result_type max_val = ldexp(static_cast<result_type>(1), std::numeric_limits<int>::digits);
+   #endif   
+
+   if(r >= max_val || r < -max_val)
    {
       return static_cast<int>(policies::raise_rounding_error("boost::math::itrunc<%1%>(%1%)", nullptr, static_cast<result_type>(v), 0, pol));
    }
@@ -85,7 +100,14 @@ inline long ltrunc(const T& v, const Policy& pol)
    BOOST_MATH_STD_USING
    using result_type = tools::promote_args_t<T>;
    result_type r = boost::math::trunc(v, pol);
-   if(r > static_cast<result_type>((std::numeric_limits<long>::max)()) || r < static_cast<result_type>((std::numeric_limits<long>::min)()))
+
+   #ifdef BOOST_MATH_HAS_CONSTEXPR_LDEXP
+   constexpr result_type max_val = boost::math::ccmath::ldexp(static_cast<result_type>(1), std::numeric_limits<long>::digits);
+   #else
+   static const result_type max_val = ldexp(static_cast<result_type>(1), std::numeric_limits<long>::digits);
+   #endif
+
+   if(r >= max_val || r < -max_val)
    {
       return static_cast<long>(policies::raise_rounding_error("boost::math::ltrunc<%1%>(%1%)", nullptr, static_cast<result_type>(v), 0L, pol));
    }
@@ -103,8 +125,14 @@ inline long long lltrunc(const T& v, const Policy& pol)
    BOOST_MATH_STD_USING
    using result_type = tools::promote_args_t<T>;
    result_type r = boost::math::trunc(v, pol);
-   if(r > static_cast<result_type>((std::numeric_limits<long long>::max)()) ||
-      r < static_cast<result_type>((std::numeric_limits<long long>::min)()))
+
+   #ifdef BOOST_MATH_HAS_CONSTEXPR_LDEXP
+   constexpr result_type max_val = boost::math::ccmath::ldexp(static_cast<result_type>(1), std::numeric_limits<long long>::digits);
+   #else
+   static const result_type max_val = ldexp(static_cast<result_type>(1), std::numeric_limits<long long>::digits);
+   #endif
+
+   if(r >= max_val || r < -max_val)
    {
       return static_cast<long long>(policies::raise_rounding_error("boost::math::lltrunc<%1%>(%1%)", nullptr, v, static_cast<long long>(0), pol));
    }
diff --git a/test/git_issue_430.cpp b/test/git_issue_430.cpp
index 236168179..053c9c553 100644
--- a/test/git_issue_430.cpp
+++ b/test/git_issue_430.cpp
@@ -7,6 +7,7 @@
 // See: https://godbolt.org/z/Ev4ManrsW
 
 #include <boost/math/special_functions/round.hpp>
+#include <boost/math/special_functions/trunc.hpp>
 #include <boost/math/special_functions/next.hpp>
 #define BOOST_TEST_MAIN
 #include <boost/test/unit_test.hpp>
@@ -94,12 +95,103 @@ void test_iround_near_boundary()
     }  
 }
 
+template <typename Real>
+void test_lltrunc_near_boundary()
+{
+   using std::ldexp;
+   Real boundary = ldexp(static_cast<Real>(1), std::numeric_limits<long long>::digits);
+
+   Real value;
+   int i;    
+
+    for (value = boundary, i = 0; i < 100; value = boost::math::float_next(value), ++i)
+    {
+        BOOST_CHECK_THROW(boost::math::lltrunc(value), boost::math::rounding_error);
+    }
+    for (value = boost::math::float_prior(boundary), i = 0; i < 1000; value = boost::math::float_prior(value), ++i)
+    {
+        BOOST_CHECK_EQUAL(static_cast<Real>(boost::math::lltrunc(value)), boost::math::lltrunc(value));
+    }
+    for (value = boost::math::float_prior(-boundary), i = 0; i < 100; value = boost::math::float_prior(value), ++i)
+    {
+        BOOST_CHECK_THROW(boost::math::lltrunc(value), boost::math::rounding_error);
+    }
+    for (value = -boundary, i = 0; i < 1000; value = boost::math::float_next(value), ++i)
+    {
+        BOOST_CHECK_EQUAL(static_cast<Real>(boost::math::lltrunc(value)), boost::math::lltrunc(value));
+    } 
+}
+
+template <typename Real>
+void test_ltrunc_near_boundary()
+{
+   using std::ldexp;
+   Real boundary = ldexp(static_cast<Real>(1), std::numeric_limits<long>::digits);
+
+   Real value;
+   int i;    
+
+    for (value = boundary, i = 0; i < 100; value = boost::math::float_next(value), ++i)
+    {
+        BOOST_CHECK_THROW(boost::math::ltrunc(value), boost::math::rounding_error);
+    }
+    for (value = boost::math::float_prior(boundary), i = 0; i < 1000; value = boost::math::float_prior(value), ++i)
+    {
+        BOOST_CHECK_EQUAL(static_cast<Real>(boost::math::ltrunc(value)), boost::math::ltrunc(value));
+    }
+    for (value = boost::math::float_prior(-boundary), i = 0; i < 100; value = boost::math::float_prior(value), ++i)
+    {
+        BOOST_CHECK_THROW(boost::math::ltrunc(value), boost::math::rounding_error);
+    }
+    for (value = -boundary, i = 0; i < 1000; value = boost::math::float_next(value), ++i)
+    {
+        BOOST_CHECK_EQUAL(static_cast<Real>(boost::math::ltrunc(value)), boost::math::ltrunc(value));
+    } 
+}
+
+template <typename Real>
+void test_itrunc_near_boundary()
+{
+   using std::ldexp;
+   Real boundary = ldexp(static_cast<Real>(1), std::numeric_limits<int>::digits);
+
+   Real value;
+   int i;    
+
+    for (value = boundary, i = 0; i < 100; value = boost::math::float_next(value), ++i)
+    {
+        BOOST_CHECK_THROW(boost::math::itrunc(value), boost::math::rounding_error);
+    }
+    for (value = boost::math::float_prior(boundary), i = 0; i < 1000; value = boost::math::float_prior(value), ++i)
+    {
+        BOOST_CHECK_EQUAL(static_cast<Real>(boost::math::itrunc(value)), boost::math::itrunc(value));
+    }
+    for (value = boost::math::float_prior(-boundary), i = 0; i < 100; value = boost::math::float_prior(value), ++i)
+    {
+        BOOST_CHECK_THROW(boost::math::itrunc(value), boost::math::rounding_error);
+    }
+    for (value = -boundary, i = 0; i < 1000; value = boost::math::float_next(value), ++i)
+    {
+        BOOST_CHECK_EQUAL(static_cast<Real>(boost::math::itrunc(value)), boost::math::itrunc(value));
+    } 
+}
+
+
 BOOST_AUTO_TEST_CASE( test_main )
 {
+    // Round
     test_llround_near_boundary<float>();
     test_llround_near_boundary<double>();
 
     test_lround_near_boundary<float>();
 
     test_iround_near_boundary<float>();
+
+    // Trunc
+    test_lltrunc_near_boundary<float>();
+    test_lltrunc_near_boundary<double>();
+
+    test_ltrunc_near_boundary<float>();
+
+    test_itrunc_near_boundary<float>();
 }