From c3dee50e5bee92564d6da23a4310c099218b4b56 Mon Sep 17 00:00:00 2001
From: King_DuckZ <king_duckz@gmx.com>
Date: Thu, 13 Apr 2017 19:21:25 +0100
Subject: [PATCH] Don't use pow and log10 directly because it causes an
 overflow.

---
 include/duckhandy/lexical_cast.hpp | 6 +++++-
 test/unit/lexical_cast_test.cpp    | 5 +++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/duckhandy/lexical_cast.hpp b/include/duckhandy/lexical_cast.hpp
index 3ad1877..0bcb5ff 100644
--- a/include/duckhandy/lexical_cast.hpp
+++ b/include/duckhandy/lexical_cast.hpp
@@ -166,11 +166,15 @@ namespace dhandy {
 		template <typename T>
 		template <std::size_t... Powers, std::size_t... Digits>
 		std::size_t dec<T>::count_digits_implem (T parValue, dhandy::bt::index_seq<Powers...>, dhandy::bt::index_seq<Digits...>) {
+			static_assert(sizeof...(Digits) == CHAR_BIT * sizeof(T) + 1, "Too many values for Digits");
 			typedef typename std::make_unsigned<T>::type UT;
 			static constexpr UT powers[] = { 0, static_cast<UT>(dhandy::implem::power<10, Powers + 1>::value)... };
-			static constexpr std::size_t maxdigits[] = { count_digits_bt(static_cast<T>(sprout::pow(2.0, Digits))) - (std::numeric_limits<T>::is_signed ? 1 : 0)... };
+			//the maxdigits table is [len(str(pow(2,b))) for b in range(0,MAX_BITS)]
+			static constexpr std::size_t maxdigits[] = { static_cast<std::size_t>(static_cast<double>(Digits) / sprout::log2(10.0)) + 1 ... };
+			static_assert(maxdigits[sizeof(maxdigits) / sizeof(maxdigits[0]) - 1] <= std::numeric_limits<T>::max(), "Last item in maxdigits overflows T");
 			const auto bits = sizeof(parValue) * CHAR_BIT - dhandy::implem::count_leading_zeroes<T>(dhandy::implem::abs(parValue));
 			static_assert(std::is_same<UT, decltype(dhandy::implem::abs(parValue))>::value, "Unexpected type");
+			assert(bits < sizeof(maxdigits) / sizeof(maxdigits[0]));
 			return (dhandy::implem::abs(parValue) < powers[maxdigits[bits] - 1] ? maxdigits[bits] - 1 : maxdigits[bits]) + dhandy::implem::is_negative<T>::check(parValue);
 		}
 
diff --git a/test/unit/lexical_cast_test.cpp b/test/unit/lexical_cast_test.cpp
index 98dc0b6..bee3d1e 100644
--- a/test/unit/lexical_cast_test.cpp
+++ b/test/unit/lexical_cast_test.cpp
@@ -78,4 +78,9 @@ TEST_CASE ("Check string to int conversions", "[s2i][lexical_cast]") {
 }
 
 TEST_CASE ("Check int to string conversions", "[i2s][lexical_cast]") {
+	using std::string;
+	using dhandy::lexical_cast;
+
+	CHECK(lexical_cast<string>(1) == "1");
+	CHECK(lexical_cast<string>(static_cast<uint16_t>(0xFFFF)) == "65535");
 }