Add constexpr Float power(Float base, Exponent exponent).

Author: evoskuil

include/bitcoin/system/impl/math/power.ipp

@@ -112,6 +112,23 @@ constexpr Value power2(Exponent exponent) NOEXCEPT
         possible_narrow_and_sign_cast<unsigned>(exponent));
 }
 
+template <typename Float, typename Exponent,
+    if_floating_point<Float>,
+    if_unsigned_integer<Exponent>>
+constexpr Float power(Float base, Exponent exponent) NOEXCEPT
+{
+    // 0^0 is undefined, return 0.
+    if ((base == 0.0) && is_zero(exponent))
+        return 0.0;
+
+    Float product{ 1.0 };
+    while (exponent-- > 0u)
+        if ((product *= base) == 0.0)
+            break;
+
+    return product;
+}
+
 } // namespace system
 } // namespace libbitcoin
 

include/bitcoin/system/math/power.hpp

@@ -54,6 +54,12 @@ template <typename Value = size_t, typename Exponent,
     if_unsigned_integer<Exponent> = true>
 constexpr Value power2(Exponent exponent) NOEXCEPT;
 
+/// Floating point constexpr optimization for integer exponent.
+template <typename Float, typename Exponent,
+    if_floating_point<Float> = true,
+    if_unsigned_integer<Exponent> = true>
+constexpr Float power(Float base, Exponent exponent) NOEXCEPT;
+
 } // namespace system
 } // namespace libbitcoin
 

test/math/power.cpp

@@ -66,10 +66,25 @@ static_assert(power<3, size_t>(0u) == 1u);
 // uint256_t
 static_assert(power<2u, uint256_t>(10u) == 1024u);
 
-// uintx is not constexpr.
+
+// floating point
+static_assert(is_same_type<decltype(power(0.0f, 0u)), float>);
+static_assert(is_same_type<decltype(power(0.0, 0u)), double>);
+
+static_assert(power(0.0f, 0u) == 0.0f);
+static_assert(power(0.0, 0u) == 0.0);
+static_assert(power(1.0, 0u) == 1.0);
+static_assert(power(1.0, 1u) == 1.0);
+static_assert(power(2.0, 1u) == 2.0);
+static_assert(power(2.0, 2u) == 4.0);
+static_assert(power(3.0, 3u) == 27.0);
+
+// Actually 311.1696 but this is the floating point representation.
+static_assert(power(4.2, 4u) == 311.16960000000006);
 
 BOOST_AUTO_TEST_SUITE(power_tests)
 
+// uintx is not constexpr.
 BOOST_AUTO_TEST_CASE(power_uintx_tests)
 {
     BOOST_REQUIRE(true);