Merge pull request #546 from cppalliance/pow10_in_pow

Fix #205 via powers of 10 in pow() function

Author: ckormanyos

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

@@ -123,28 +123,53 @@ constexpr auto pow(T b, IntegralType p) noexcept
         {
             result = one;
         }
-        else BOOST_DECIMAL_IF_CONSTEXPR (std::is_signed<local_integral_type>::value)
+        else
         {
-            if(p < static_cast<local_integral_type>(UINT8_C(0)))
+            int exp10val { };
+
+            const auto bn { frexp10(b, &exp10val) };
+
+            const auto
+                zeros_removal
+                {
+                    detail::remove_trailing_zeros(bn)
+                };
+
+            const bool is_pure { static_cast<int>(zeros_removal.trimmed_number) == 1 };
+
+            if(is_pure)
             {
-                const auto up =
-                    static_cast<local_unsigned_integral_type>
-                    (
-                          static_cast<local_unsigned_integral_type>(~p)
-                        + static_cast<local_unsigned_integral_type>(UINT8_C(1))
-                    );
+                // Here, a pure power-of-10 argument (b) gets a pure integral result.
+                const int log10_val { exp10val + static_cast<int>(zeros_removal.number_of_removed_zeros) };
 
-                result = one / detail::pow_n_impl(b, up);
+                result = T { 1, static_cast<int>(log10_val * static_cast<int>(p)) };
             }
             else
             {
-                result = detail::pow_n_impl(b, static_cast<local_unsigned_integral_type>(p));
+                BOOST_DECIMAL_IF_CONSTEXPR (std::is_signed<local_integral_type>::value)
+                {
+                    if(p < static_cast<local_integral_type>(UINT8_C(0)))
+                    {
+                        const auto up =
+                            static_cast<local_unsigned_integral_type>
+                            (
+                                  static_cast<local_unsigned_integral_type>(~p)
+                                + static_cast<local_unsigned_integral_type>(UINT8_C(1))
+                            );
+
+                        result = one / detail::pow_n_impl(b, up);
+                    }
+                    else
+                    {
+                        result = detail::pow_n_impl(b, static_cast<local_unsigned_integral_type>(p));
+                    }
+                }
+                else
+                {
+                    result = detail::pow_n_impl(b, static_cast<local_unsigned_integral_type>(p));
+                }
             }
         }
-        else
-        {
-            result = detail::pow_n_impl(b, static_cast<local_unsigned_integral_type>(p));
-        }
     }
 
     return result;

test/link_1.cpp

@@ -6,6 +6,7 @@
 
 void test_odr_use(const boost::decimal::rounding_mode*);
 
+// LCOV_EXCL_START
 template <typename T>
 void test()
 {
@@ -18,3 +19,4 @@ void f1()
     test<boost::decimal::decimal64>();
     test<boost::decimal::decimal128>();
 }
+// LCOV_EXCL_STOP

test/link_2.cpp

@@ -6,6 +6,7 @@
 
 void test_odr_use(const boost::decimal::rounding_mode*);
 
+// LCOV_EXCL_START
 template <typename T>
 void test()
 {
@@ -18,3 +19,4 @@ void f2()
     test<boost::decimal::decimal64>();
     test<boost::decimal::decimal128>();
 }
+// LCOV_EXCL_STOP

test/link_3.cpp

@@ -4,6 +4,7 @@
 
 #include <boost/decimal.hpp>
 
+// LCOV_EXCL_START
 void f1();
 void f2();
 
@@ -16,3 +17,4 @@ int main()
 void test_odr_use(const boost::decimal::rounding_mode*)
 {
 }
+// LCOV_EXCL_STOP

test/test_acosh.cpp

@@ -56,7 +56,7 @@ namespace local
 
     if(b == static_cast<NumericType>(0))
     {
-      result_is_ok = (fabs(a - b) < tol);
+      result_is_ok = (fabs(a - b) < tol); // LCOV_EXCL_LINE
     }
     else
     {

test/test_asinh.cpp

@@ -22,7 +22,6 @@
 #include <boost/core/lightweight_test.hpp>
 
 auto my_zero() -> boost::decimal::decimal32&;
-auto my_one () -> boost::decimal::decimal32&;
 
 namespace local
 {
@@ -56,7 +55,7 @@ namespace local
 
     if(b == static_cast<NumericType>(0))
     {
-      result_is_ok = (fabs(a - b) < tol);
+      result_is_ok = (fabs(a - b) < tol); // LCOV_EXCL_LINE
     }
     else
     {
@@ -268,4 +267,3 @@ auto main() -> int
 }
 
 auto my_zero() -> boost::decimal::decimal32& { static boost::decimal::decimal32 val_zero { 0, 0 }; return val_zero; }
-auto my_one () -> boost::decimal::decimal32& { static boost::decimal::decimal32 val_one  { 1, 0 }; return val_one; }

test/test_atanh.cpp

@@ -56,7 +56,7 @@ namespace local
 
     if(b == static_cast<NumericType>(0))
     {
-      result_is_ok = (fabs(a - b) < tol);
+      result_is_ok = (fabs(a - b) < tol); // LCOV_EXCL_LINE
     }
     else
     {

test/test_edges_and_behave.cpp

@@ -62,7 +62,7 @@ namespace local
 
     if(b == static_cast<NumericType>(0))
     {
-      result_is_ok = (fabs(a - b) < tol);
+      result_is_ok = (fabs(a - b) < tol); // LCOV_EXCL_LINE
     }
     else
     {

test/test_expm1.cpp

@@ -55,7 +55,7 @@ namespace local
 
     if(b == static_cast<NumericType>(0))
     {
-      result_is_ok = (fabs(a - b) < tol);
+      result_is_ok = (fabs(a - b) < tol); // LCOV_EXCL_LINE
     }
     else
     {

test/test_frexp_ldexp.cpp

@@ -53,7 +53,7 @@ namespace local
 
     if(b == static_cast<NumericType>(0))
     {
-      result_is_ok = (fabs(a - b) < tol);
+      result_is_ok = (fabs(a - b) < tol); // LCOV_EXCL_LINE
     }
     else
     {