Merge pull request #1130 from cppalliance/1110v2

Fix detection of pure powers of 10 for large significands

Author: mborland

include/boost/decimal/detail/cmath/cbrt.hpp

@@ -61,7 +61,7 @@ constexpr auto cbrt_impl(const T x) noexcept
                 remove_trailing_zeros(gn)
             };
 
-        const bool is_pure { static_cast<unsigned>(zeros_removal.trimmed_number) == 1U };
+        const bool is_pure { zeros_removal.trimmed_number == 1U };
 
         if(is_pure)
         {

include/boost/decimal/detail/cmath/log10.hpp

@@ -63,7 +63,7 @@ constexpr auto log10_impl(const T x) noexcept
                 remove_trailing_zeros(gn)
             };
 
-        const bool is_pure { static_cast<unsigned>(zeros_removal.trimmed_number) == 1U };
+        const bool is_pure { zeros_removal.trimmed_number == 1U };
 
         if(is_pure)
         {

include/boost/decimal/detail/cmath/sqrt.hpp

@@ -61,7 +61,7 @@ constexpr auto sqrt_impl(const T x) noexcept
                 remove_trailing_zeros(gn)
             };
 
-        const bool is_pure { static_cast<unsigned>(zeros_removal.trimmed_number) == 1U };
+        const bool is_pure { zeros_removal.trimmed_number == 1U };
 
         constexpr T one { 1 };
 

include/boost/decimal/detail/power_tables.hpp

@@ -70,6 +70,7 @@ run github_issue_1057.cpp ;
 compile-fail github_issue_1087.cpp ;
 run github_issue_1091.cpp ;
 run github_issue_1094.cpp ;
+run github_issue_1110.cpp ;
 run github_issue_1112.cpp ;
 
 run link_1.cpp link_2.cpp link_3.cpp ;

test/Jamfile

@@ -0,0 +1,68 @@
+// Copyright 2025 Christopher Kormanyos
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+//
+// See: https://github.com/cppalliance/decimal/issues/1110
+
+#include <boost/decimal/decimal128_t.hpp>
+#include <boost/decimal/cmath.hpp>
+#include <boost/decimal/iostream.hpp>
+
+#include <boost/core/lightweight_test.hpp>
+
+#include <iomanip>
+#include <iostream>
+#include <sstream>
+
+using namespace boost::decimal;
+
+namespace local {
+
+auto test() -> void;
+
+auto test() -> void
+{
+    const boost::decimal::decimal128_t one { 1 };
+    const boost::decimal::decimal128_t del { 1, -32 };
+    const boost::decimal::decimal128_t sum { one + del };
+
+    const boost::decimal::decimal128_t sqr { sqrt(sum) };
+
+    {
+        std::stringstream strm { };
+
+        strm << std::setprecision(std::numeric_limits<boost::decimal::decimal128_t>::digits10) << sqr;
+
+        BOOST_TEST_CSTR_EQ(strm.str().c_str(), "1.000000000000000000000000000000005");
+    }
+
+    const boost::decimal::decimal128_t cbr { cbrt(sum) };
+
+    {
+        std::stringstream strm { };
+
+        strm << std::setprecision(std::numeric_limits<boost::decimal::decimal128_t>::digits10)<< cbr;
+
+        // TODO: This tolerance isn't the best
+        BOOST_TEST_CSTR_EQ(strm.str().c_str(), "1.000000000000000000000000000000641");
+    }
+
+    const boost::decimal::decimal128_t lgt { log10(sum) };
+
+    {
+        std::stringstream strm { };
+
+        strm << std::setprecision(std::numeric_limits<boost::decimal::decimal128_t>::digits10)<< lgt;
+
+        BOOST_TEST_CSTR_EQ(strm.str().c_str(), "4.4e-33");
+    }
+}
+
+} // namespace local
+
+auto main() -> int
+{
+    local::test();
+
+    return boost::report_errors();
+}

test/github_issue_1110.cpp

@@ -39,30 +39,11 @@ void test()
 void test_extended()
 {
     using namespace boost::decimal;
-    constexpr std::array<boost::int128::uint128_t, 18> powers_of_10 =
-    {{
-        boost::int128::uint128_t {UINT64_C(0x5), UINT64_C(0x6BC75E2D63100000)},
-        boost::int128::uint128_t {UINT64_C(0x36), UINT64_C(0x35C9ADC5DEA00000)},
-        boost::int128::uint128_t {UINT64_C(0x21E), UINT64_C(0x19E0C9BAB2400000)},
-        boost::int128::uint128_t {UINT64_C(0x152D), UINT64_C(0x02C7E14AF6800000)},
-        boost::int128::uint128_t {UINT64_C(0x84595), UINT64_C(0x161401484A000000)},
-        boost::int128::uint128_t {UINT64_C(0x52B7D2), UINT64_C(0xDCC80CD2E4000000)},
-        boost::int128::uint128_t {UINT64_C(0x33B2E3C), UINT64_C(0x9FD0803CE8000000)},
-        boost::int128::uint128_t {UINT64_C(0x204FCE5E), UINT64_C(0x3E25026110000000)},
-        boost::int128::uint128_t {UINT64_C(0x1431E0FAE), UINT64_C(0x6D7217CAA0000000)},
-        boost::int128::uint128_t {UINT64_C(0xC9F2C9CD0), UINT64_C(0x4674EDEA40000000)},
-        boost::int128::uint128_t {UINT64_C(0x7E37BE2022), UINT64_C(0xC0914B2680000000)},
-        boost::int128::uint128_t {UINT64_C(0x4EE2D6D415B), UINT64_C(0x85ACEF8100000000)},
-        boost::int128::uint128_t {UINT64_C(0x314DC6448D93), UINT64_C(0x38C15B0A00000000)},
-        boost::int128::uint128_t {UINT64_C(0x1ED09BEAD87C0), UINT64_C(0x378D8E6400000000)},
-        boost::int128::uint128_t {UINT64_C(0x13426172C74D82), UINT64_C(0x2B878FE800000000)},
-        boost::int128::uint128_t {UINT64_C(0xC097CE7BC90715), UINT64_C(0xB34B9F1000000000)},
-        boost::int128::uint128_t {UINT64_C(0x785EE10D5DA46D9), UINT64_C(0x00F436A000000000)},
-        boost::int128::uint128_t {UINT64_C(0x4B3B4CA85A86C47A), UINT64_C(0x098A224000000000)}
-     }};
+    const auto powers_of_10 = detail::impl::BOOST_DECIMAL_DETAIL_INT128_pow10;
 
-    for (const auto& val : powers_of_10)
+    for (std::size_t i {}; i < 39; ++i)
     {
+        const auto val = powers_of_10[i];
         const auto temp {boost::decimal::detail::remove_trailing_zeros(val)};
         if (!BOOST_TEST_EQ(temp.trimmed_number, boost::int128::uint128_t(1)))
         {