From f3e0cde514e444c2e25a3522d05a6e244fb2f23a Mon Sep 17 00:00:00 2001
From: jzmaddock <john@johnmaddock.co.uk>
Date: Fri, 17 May 2024 19:17:04 +0100
Subject: [PATCH 1/2] Correct float_next(+INF) and float_prior(-INF) Fixes
 https://github.com/boostorg/math/issues/1132

---
 include/boost/math/special_functions/next.hpp | 32 ++++++++++++++-----
 test/test_next.cpp                            | 11 +++++--
 2 files changed, 32 insertions(+), 11 deletions(-)

diff --git a/include/boost/math/special_functions/next.hpp b/include/boost/math/special_functions/next.hpp
index c696b97b5..02a208e4e 100644
--- a/boost/math/special_functions/next.hpp
+++ b/boost/math/special_functions/next.hpp
@@ -194,10 +194,14 @@ T float_next_imp(const T& val, const std::true_type&, const Policy& pol)
 
    int fpclass = (boost::math::fpclassify)(val);
 
-   if((fpclass == (int)FP_NAN) || (fpclass == (int)FP_INFINITE))
+   if (fpclass == (int)FP_INFINITE)
    {
-      if(val < 0)
+      if (val < 0)
          return -tools::max_value<T>();
+      return val;  // +INF
+   }
+   else if (fpclass == (int)FP_NAN)
+   {
       return policies::raise_domain_error<T>(
          function,
          "Argument must be finite, but got %1%", val, pol);
@@ -243,10 +247,14 @@ T float_next_imp(const T& val, const std::false_type&, const Policy& pol)
 
    int fpclass = (boost::math::fpclassify)(val);
 
-   if((fpclass == (int)FP_NAN) || (fpclass == (int)FP_INFINITE))
+   if (fpclass == (int)FP_INFINITE)
    {
-      if(val < 0)
+      if (val < 0)
          return -tools::max_value<T>();
+      return val;  // +INF
+   }
+   else if (fpclass == (int)FP_NAN)
+   {
       return policies::raise_domain_error<T>(
          function,
          "Argument must be finite, but got %1%", val, pol);
@@ -328,10 +336,14 @@ T float_prior_imp(const T& val, const std::true_type&, const Policy& pol)
 
    int fpclass = (boost::math::fpclassify)(val);
 
-   if((fpclass == (int)FP_NAN) || (fpclass == (int)FP_INFINITE))
+   if (fpclass == (int)FP_INFINITE)
    {
-      if(val > 0)
+      if (val > 0)
          return tools::max_value<T>();
+      return val; // -INF
+   }
+   else if (fpclass == (int)FP_NAN)
+   {
       return policies::raise_domain_error<T>(
          function,
          "Argument must be finite, but got %1%", val, pol);
@@ -378,10 +390,14 @@ T float_prior_imp(const T& val, const std::false_type&, const Policy& pol)
 
    int fpclass = (boost::math::fpclassify)(val);
 
-   if((fpclass == (int)FP_NAN) || (fpclass == (int)FP_INFINITE))
+   if (fpclass == (int)FP_INFINITE)
    {
-      if(val > 0)
+      if (val > 0)
          return tools::max_value<T>();
+      return val; // -INF
+   }
+   else if (fpclass == (int)FP_NAN)
+   {
       return policies::raise_domain_error<T>(
          function,
          "Argument must be finite, but got %1%", val, pol);
diff --git a/test/test_next.cpp b/test/test_next.cpp
index b4f05b437..8bb5f8d99 100644
--- a/libs/math/test/test_next.cpp
+++ b/libs/math/test/test_next.cpp
@@ -171,12 +171,12 @@ void test_values(const T& val, const char* name)
       BOOST_CHECK_EQUAL(boost::math::float_advance(val, primes[i]), v1);
       BOOST_CHECK_EQUAL(boost::math::float_advance(val, -primes[i]), v2);
    }
-   if(std::numeric_limits<T>::is_specialized && (std::numeric_limits<T>::has_infinity))
+   BOOST_IF_CONSTEXPR(std::numeric_limits<T>::is_specialized && (std::numeric_limits<T>::has_infinity))
    {
       BOOST_CHECK_EQUAL(boost::math::float_prior(std::numeric_limits<T>::infinity()), (std::numeric_limits<T>::max)());
       BOOST_CHECK_EQUAL(boost::math::float_next(-std::numeric_limits<T>::infinity()), -(std::numeric_limits<T>::max)());
-      BOOST_MATH_CHECK_THROW(boost::math::float_prior(-std::numeric_limits<T>::infinity()), std::domain_error);
-      BOOST_MATH_CHECK_THROW(boost::math::float_next(std::numeric_limits<T>::infinity()), std::domain_error);
+      BOOST_CHECK_EQUAL(boost::math::float_prior(-std::numeric_limits<T>::infinity()), -std::numeric_limits<T>::infinity());
+      BOOST_CHECK_EQUAL(boost::math::float_next(std::numeric_limits<T>::infinity()), std::numeric_limits<T>::infinity());
       if(boost::math::policies:: BOOST_MATH_OVERFLOW_ERROR_POLICY == boost::math::policies::throw_on_error)
       {
          BOOST_MATH_CHECK_THROW(boost::math::float_prior(-(std::numeric_limits<T>::max)()), std::overflow_error);
@@ -188,6 +188,11 @@ void test_values(const T& val, const char* name)
          BOOST_CHECK_EQUAL(boost::math::float_next((std::numeric_limits<T>::max)()), std::numeric_limits<T>::infinity());
       }
    }
+   BOOST_IF_CONSTEXPR(std::numeric_limits<T>::is_specialized && (std::numeric_limits<T>::has_quiet_NaN))
+   {
+      BOOST_MATH_CHECK_THROW(boost::math::float_prior((std::numeric_limits<T>::quiet_NaN)()), std::domain_error);
+      BOOST_MATH_CHECK_THROW(boost::math::float_next((std::numeric_limits<T>::quiet_NaN)()), std::domain_error);
+   }
    //
    // We need to test float_distance over multiple orders of magnitude,
    // the only way to get an accurate true result is to count the representations
-- 
2.45.1