From 2859c22009d3f91d3a33d66414f14e6c88b17b5c Mon Sep 17 00:00:00 2001
From: cryptocode <stein@nano.org>
Date: Wed, 19 Feb 2020 11:29:29 +0100
Subject: [PATCH] Add GSL-style narrow_cast (#2567)

---
 nano/lib/utility.hpp    | 10 ++++++++++
 nano/node/election.cpp  |  8 ++++----
 nano/node/telemetry.cpp |  2 +-
 3 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/nano/lib/utility.hpp b/nano/lib/utility.hpp
index 4b66d3feb..debec4689 100644
--- a/nano/lib/utility.hpp
+++ b/nano/lib/utility.hpp
@@ -2,6 +2,7 @@
 
 #include <nano/lib/locks.hpp>
 
+#include <cassert>
 #include <functional>
 #include <mutex>
 #include <vector>
@@ -161,6 +162,15 @@ void transform_if (InputIt first, InputIt last, OutputIt dest, Pred pred, Func t
 		++first;
 	}
 }
+
+/** Safe narrowing cast which silences warnings and asserts on data loss in debug builds. This is optimized away. */
+template <typename TARGET_TYPE, typename SOURCE_TYPE>
+constexpr TARGET_TYPE narrow_cast (SOURCE_TYPE const & val)
+{
+	auto res (static_cast<TARGET_TYPE> (val));
+	assert (val == static_cast<SOURCE_TYPE> (res));
+	return res;
+}
 }
 
 void release_assert_internal (bool check, const char * check_expr, const char * file, unsigned int line);
diff --git a/nano/node/election.cpp b/nano/node/election.cpp
index 3e816159f..4f6131a5f 100644
--- a/nano/node/election.cpp
+++ b/nano/node/election.cpp
@@ -31,8 +31,8 @@ void nano::election::confirm_once (nano::election_status_type type_a)
 		status.election_end = std::chrono::duration_cast<std::chrono::milliseconds> (std::chrono::system_clock::now ().time_since_epoch ());
 		status.election_duration = std::chrono::duration_cast<std::chrono::milliseconds> (std::chrono::steady_clock::now () - election_start);
 		status.confirmation_request_count = confirmation_request_count;
-		status.block_count = blocks.size ();
-		status.voter_count = last_votes.size ();
+		status.block_count = nano::narrow_cast<decltype (status.block_count)> (blocks.size ());
+		status.voter_count = nano::narrow_cast<decltype (status.voter_count)> (last_votes.size ());
 		status.type = type_a;
 		auto status_l (status);
 		auto node_l (node.shared ());
@@ -57,8 +57,8 @@ void nano::election::stop ()
 		status.election_end = std::chrono::duration_cast<std::chrono::milliseconds> (std::chrono::system_clock::now ().time_since_epoch ());
 		status.election_duration = std::chrono::duration_cast<std::chrono::milliseconds> (std::chrono::steady_clock::now () - election_start);
 		status.confirmation_request_count = confirmation_request_count;
-		status.block_count = blocks.size ();
-		status.voter_count = last_votes.size ();
+		status.block_count = nano::narrow_cast<decltype (status.block_count)> (blocks.size ());
+		status.voter_count = nano::narrow_cast<decltype (status.voter_count)> (last_votes.size ());
 		status.type = nano::election_status_type::stopped;
 	}
 }
diff --git a/nano/node/telemetry.cpp b/nano/node/telemetry.cpp
index 18a68d431..508d34811 100644
--- a/nano/node/telemetry.cpp
+++ b/nano/node/telemetry.cpp
@@ -680,7 +680,7 @@ nano::telemetry_data nano::local_telemetry_data (nano::ledger_cache const & ledg
 	telemetry_data.uptime = std::chrono::duration_cast<std::chrono::seconds> (std::chrono::steady_clock::now () - statup_time_a).count ();
 	telemetry_data.unchecked_count = ledger_cache_a.unchecked_count;
 	telemetry_data.genesis_block = network_params_a.ledger.genesis_hash;
-	telemetry_data.peer_count = network_a.size ();
+	telemetry_data.peer_count = nano::narrow_cast<decltype (telemetry_data.peer_count)> (network_a.size ());
 	telemetry_data.account_count = ledger_cache_a.account_count;
 	telemetry_data.major_version = nano::get_major_node_version ();
 	telemetry_data.minor_version = nano::get_minor_node_version ();