Add functionality testing

Author: mborland

test/Jamfile

@@ -149,6 +149,7 @@ run-fail test_fprintf.cpp ;
 run test_frexp_ldexp.cpp ;
 run test_from_chars.cpp /boost/charconv//boost_charconv ;
 run test_from_chars_nan_payloads.cpp ;
+run test_from_string.cpp ;
 run test_git_issue_266.cpp ;
 run test_git_issue_271.cpp ;
 run test_hash.cpp ;

test/test_from_string.cpp

@@ -0,0 +1,90 @@
+// Copyright 2025 Matt Borland
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/decimal.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <random>
+#include <string>
+
+using namespace boost::decimal;
+
+static std::mt19937_64 rng {42};
+static constexpr std::size_t N {1024};
+
+template <typename T>
+T recover_value(const std::string& str, std::size_t* ptr);
+
+template <>
+decimal32_t recover_value<decimal32_t>(const std::string& str, std::size_t* ptr)
+{
+    return stod32(str, ptr);
+}
+
+template <>
+decimal_fast32_t recover_value<decimal_fast32_t>(const std::string& str, std::size_t* ptr)
+{
+    return stod32f(str, ptr);
+}
+
+template <>
+decimal64_t recover_value<decimal64_t>(const std::string& str, std::size_t* ptr)
+{
+    return stod64(str, ptr);
+}
+
+template <>
+decimal_fast64_t recover_value<decimal_fast64_t>(const std::string& str, std::size_t* ptr)
+{
+    return stod64f(str, ptr);
+}
+
+template <>
+decimal128_t recover_value<decimal128_t>(const std::string& str, std::size_t* ptr)
+{
+    return stod128(str, ptr);
+}
+
+template <>
+decimal_fast128_t recover_value<decimal_fast128_t>(const std::string& str, std::size_t* ptr)
+{
+    return stod128f(str, ptr);
+}
+
+template <typename T>
+void test()
+{
+    std::uniform_int_distribution<std::int32_t> sig_dist {-9'999'999, 9'999'999};
+    std::uniform_int_distribution<std::int32_t> exp_dist {-50, 50};
+
+    for (std::size_t i {}; i < N; ++i)
+    {
+        const T val {sig_dist(rng), exp_dist(rng)};
+
+        char buffer[64];
+        const auto r {to_chars(buffer, buffer + sizeof(buffer), val)};
+        BOOST_TEST(r);
+        const auto dist {static_cast<std::size_t>(r.ptr - buffer)};
+
+        *r.ptr = '\0';
+        const std::string str {buffer};
+        std::size_t idx {};
+        const T return_value {recover_value<T>(str, &idx)};
+
+        BOOST_TEST_EQ(return_value, val);
+        BOOST_TEST_EQ(idx, dist);
+    }
+}
+
+int main()
+{
+    test<decimal32_t>();
+    test<decimal_fast32_t>();
+    test<decimal64_t>();
+    test<decimal_fast64_t>();
+    test<decimal128_t>();
+    test<decimal_fast128_t>();
+
+    return boost::report_errors();
+}
+