From 2e28bd79cafb0db8be6d9688bff8e2c28fb0d311 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Reimar=20D=C3=B6ffinger?= <reimar.doeffinger@arm.com>
Date: Wed, 20 Nov 2024 17:43:52 +0100
Subject: [PATCH] Change BOOST_MATH_PROMOTE_DOUBLE_POLICY to false for non-x86

Avoids a massive performance loss due to use of emulated 128 bit types.
Fixes issue #1211.
---
 include/boost/math/policies/policy.hpp | 13 ++++++++++---
 test/test_policy_8.cpp                 |  4 ++--
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/include/boost/math/policies/policy.hpp b/include/boost/math/policies/policy.hpp
index ec7b36f2d5..d455aa9053 100644
--- a/include/boost/math/policies/policy.hpp
+++ b/include/boost/math/policies/policy.hpp
@@ -111,10 +111,17 @@ namespace policies{
 #define BOOST_MATH_PROMOTE_FLOAT_POLICY true
 #endif
 #ifndef BOOST_MATH_PROMOTE_DOUBLE_POLICY
-#ifdef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
-#define BOOST_MATH_PROMOTE_DOUBLE_POLICY false
-#else
+#if !defined(BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS) \
+    && (defined(__i386) || defined(__i386__) || defined(_M_IX86) \
+    || defined(__amd64) || defined(__amd64__)  || defined(_M_AMD64) \
+    || defined(__x86_64) || defined(__x86_64__) || defined(_M_X64))
+// On non-x86 long double is expected to be either the same as double
+// or an emulated 128 bit type - promotion is not sensible.
+// On x86 long double is also rather slow these days, but changing the
+// policy there has larger compatibility concerns and is left to a later time
 #define BOOST_MATH_PROMOTE_DOUBLE_POLICY true
+#else
+#define BOOST_MATH_PROMOTE_DOUBLE_POLICY false
 #endif
 #endif
 #ifndef BOOST_MATH_DISCRETE_QUANTILE_POLICY
diff --git a/test/test_policy_8.cpp b/test/test_policy_8.cpp
index 14a2897ad6..8b4c6b4eb2 100644
--- a/test/test_policy_8.cpp
+++ b/test/test_policy_8.cpp
@@ -39,8 +39,8 @@ BOOST_AUTO_TEST_CASE( test_main )
    BOOST_CHECK(check_same(make_policy(domain_error<ignore_error>(), pole_error<ignore_error>(), overflow_error<ignore_error>(), underflow_error<throw_on_error>(), denorm_error<throw_on_error>(), evaluation_error<ignore_error>(), indeterminate_result_error<throw_on_error>(), digits10<5>()), policy<domain_error<ignore_error>, pole_error<ignore_error>, overflow_error<ignore_error>, underflow_error<throw_on_error>, denorm_error<throw_on_error>, evaluation_error<ignore_error>, indeterminate_result_error<throw_on_error>, digits2<19> >()));
    BOOST_CHECK(check_same(make_policy(domain_error<ignore_error>(), pole_error<ignore_error>(), overflow_error<ignore_error>(), underflow_error<throw_on_error>(), denorm_error<throw_on_error>(), evaluation_error<ignore_error>(), indeterminate_result_error<throw_on_error>(), digits2<10>(), promote_float<false>()), policy<domain_error<ignore_error>, pole_error<ignore_error>, overflow_error<ignore_error>, underflow_error<throw_on_error>, denorm_error<throw_on_error>, evaluation_error<ignore_error>, indeterminate_result_error<throw_on_error>, digits2<10>, promote_float<false> >()));
 #ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
-   BOOST_CHECK(check_same(make_policy(domain_error<ignore_error>(), pole_error<ignore_error>(), overflow_error<ignore_error>(), underflow_error<throw_on_error>(), denorm_error<throw_on_error>(), evaluation_error<ignore_error>(), indeterminate_result_error<throw_on_error>(), digits2<10>(), promote_float<false>(), promote_double<false>()), policy<domain_error<ignore_error>, pole_error<ignore_error>, overflow_error<ignore_error>, underflow_error<throw_on_error>, denorm_error<throw_on_error>, evaluation_error<ignore_error>, indeterminate_result_error<throw_on_error>, digits2<10>, promote_float<false>, promote_double<false> >()));
-   BOOST_CHECK(check_same(make_policy(domain_error<ignore_error>(), pole_error<ignore_error>(), overflow_error<ignore_error>(), underflow_error<throw_on_error>(), denorm_error<throw_on_error>(), evaluation_error<ignore_error>(), indeterminate_result_error<throw_on_error>(), digits2<10>(), promote_float<false>(), promote_double<false>(), discrete_quantile<integer_round_down>()), policy<domain_error<ignore_error>, pole_error<ignore_error>, overflow_error<ignore_error>, underflow_error<throw_on_error>, denorm_error<throw_on_error>, evaluation_error<ignore_error>, indeterminate_result_error<throw_on_error>, digits2<10>, promote_float<false>, promote_double<false>, discrete_quantile<integer_round_down> >()));
+   BOOST_CHECK(check_same(make_policy(domain_error<ignore_error>(), pole_error<ignore_error>(), overflow_error<ignore_error>(), underflow_error<throw_on_error>(), denorm_error<throw_on_error>(), evaluation_error<ignore_error>(), indeterminate_result_error<throw_on_error>(), digits2<10>(), promote_float<false>(), promote_double<!BOOST_MATH_PROMOTE_DOUBLE_POLICY>()), policy<domain_error<ignore_error>, pole_error<ignore_error>, overflow_error<ignore_error>, underflow_error<throw_on_error>, denorm_error<throw_on_error>, evaluation_error<ignore_error>, indeterminate_result_error<throw_on_error>, digits2<10>, promote_float<false>, promote_double<!BOOST_MATH_PROMOTE_DOUBLE_POLICY> >()));
+   BOOST_CHECK(check_same(make_policy(domain_error<ignore_error>(), pole_error<ignore_error>(), overflow_error<ignore_error>(), underflow_error<throw_on_error>(), denorm_error<throw_on_error>(), evaluation_error<ignore_error>(), indeterminate_result_error<throw_on_error>(), digits2<10>(), promote_float<false>(), promote_double<!BOOST_MATH_PROMOTE_DOUBLE_POLICY>(), discrete_quantile<integer_round_down>()), policy<domain_error<ignore_error>, pole_error<ignore_error>, overflow_error<ignore_error>, underflow_error<throw_on_error>, denorm_error<throw_on_error>, evaluation_error<ignore_error>, indeterminate_result_error<throw_on_error>, digits2<10>, promote_float<false>, promote_double<!BOOST_MATH_PROMOTE_DOUBLE_POLICY>, discrete_quantile<integer_round_down> >()));
 #endif