diff --git a/include/libtorrent/hex.hpp b/include/libtorrent/hex.hpp
index 69299178a..f97dfbbc3 100644
--- a/include/libtorrent/hex.hpp
+++ b/include/libtorrent/hex.hpp
@@ -35,22 +35,17 @@ POSSIBILITY OF SUCH DAMAGE.
 
 #include "libtorrent/config.hpp"
 #include "libtorrent/error_code.hpp"
-
-#include "libtorrent/aux_/disable_warnings_push.hpp"
+#include "libtorrent/span.hpp"
 
 #include <string>
-#include <boost/limits.hpp>
 #include <array>
 
-#include "libtorrent/aux_/disable_warnings_pop.hpp"
-
 namespace libtorrent
 {
 	namespace aux {
 
 	TORRENT_EXTRA_EXPORT int hex_to_int(char in);
-	// TODO: 3 take an span here instead
-	TORRENT_EXTRA_EXPORT bool is_hex(char const *in, int len);
+	TORRENT_EXTRA_EXPORT bool is_hex(span<char const> in);
 
 	// The overload taking a ``std::string`` converts (binary) the string ``s``
 	// to hexadecimal representation and returns it.
@@ -58,23 +53,29 @@ namespace libtorrent
 	// buffer [``in``, ``in`` + len) to hexadecimal and prints it to the buffer
 	// ``out``. The caller is responsible for making sure the buffer pointed to
 	// by ``out`` is large enough, i.e. has at least len * 2 bytes of space.
-	TORRENT_DEPRECATED_EXPORT std::string to_hex(std::string const& s);
-	// TODO: 3 take an span here instead
-	TORRENT_DEPRECATED_EXPORT void to_hex(char const *in, int len, char* out);
+	TORRENT_DEPRECATED_EXPORT std::string to_hex(span<char const> s);
+	TORRENT_DEPRECATED_EXPORT void to_hex(span<char const> in, char* out);
 
 	// converts the buffer [``in``, ``in`` + len) from hexadecimal to
 	// binary. The binary output is written to the buffer pointed to
 	// by ``out``. The caller is responsible for making sure the buffer
 	// at ``out`` has enough space for the result to be written to, i.e.
 	// (len + 1) / 2 bytes.
-	// TODO: 3 take an span here instead
-	TORRENT_DEPRECATED_EXPORT bool from_hex(char const *in, int len, char* out);
+	TORRENT_DEPRECATED_EXPORT bool from_hex(span<char const> in, char* out);
 
 	}
 
 #ifndef TORRENT_NO_DEPRECATE
-	using aux::to_hex;
-	using aux::from_hex;
+	// deprecated in 1.2
+	TORRENT_DEPRECATED
+	inline void to_hex(char const* in, int len, char* out)
+	{ aux::to_hex({in, static_cast<size_t>(len)}, out); }
+	TORRENT_DEPRECATED
+	inline std::string to_hex(std::string const& s)
+	{ return aux::to_hex(s); }
+	TORRENT_DEPRECATED
+	inline bool from_hex(char const *in, int len, char* out)
+	{ return aux::from_hex({in, static_cast<size_t>(len)}, out); }
 #endif
 }
 
diff --git a/include/libtorrent/sha1_hash.hpp b/include/libtorrent/sha1_hash.hpp
index 799717268..5ded405df 100644
--- a/include/libtorrent/sha1_hash.hpp
+++ b/include/libtorrent/sha1_hash.hpp
@@ -131,7 +131,7 @@ namespace libtorrent
 		// shift left ``n`` bits.
 		sha1_hash& operator<<=(int n);
 
-		// shift r ``n`` bits.
+		// shift right ``n`` bits.
 		sha1_hash& operator>>=(int n);
 
 		// standard comparison operators
diff --git a/src/alert.cpp b/src/alert.cpp
index bc964d4f0..6ef9f35a3 100644
--- a/src/alert.cpp
+++ b/src/alert.cpp
@@ -76,7 +76,7 @@ namespace libtorrent {
 			else
 			{
 				char msg[41];
-				aux::to_hex(t->info_hash().data(), 20, msg);
+				aux::to_hex(t->info_hash(), msg);
 				m_name_idx = alloc.copy_string(msg);
 			}
 		}
@@ -1138,7 +1138,7 @@ namespace libtorrent {
 	{
 		error_code ec;
 		char ih_hex[41];
-		aux::to_hex(info_hash.data(), 20, ih_hex);
+		aux::to_hex(info_hash, ih_hex);
 		char msg[200];
 		std::snprintf(msg, sizeof(msg), "incoming dht announce: %s:%u (%s)"
 			, ip.to_string(ec).c_str(), port, ih_hex);
@@ -1153,7 +1153,7 @@ namespace libtorrent {
 	std::string dht_get_peers_alert::message() const
 	{
 		char ih_hex[41];
-		aux::to_hex(info_hash.data(), 20, ih_hex);
+		aux::to_hex(info_hash, ih_hex);
 		char msg[200];
 		std::snprintf(msg, sizeof(msg), "incoming dht get_peers: %s", ih_hex);
 		return msg;
@@ -1379,7 +1379,7 @@ namespace libtorrent {
 		if (params.ti) torrent_name = params.ti->name().c_str();
 		else if (!params.name.empty()) torrent_name = params.name.c_str();
 		else if (!params.url.empty()) torrent_name = params.url.c_str();
-		else aux::to_hex(params.info_hash.data(), 20, info_hash);
+		else aux::to_hex(params.info_hash, info_hash);
 
 		if (error)
 		{
@@ -1481,8 +1481,8 @@ namespace libtorrent {
 	{
 		char msg[200];
 		std::snprintf(msg, sizeof(msg), " torrent changed info-hash from: %s to %s"
-			, aux::to_hex(old_ih.to_string()).c_str()
-			, aux::to_hex(new_ih.to_string()).c_str());
+			, aux::to_hex(old_ih).c_str()
+			, aux::to_hex(new_ih).c_str());
 		return torrent_alert::message() + msg;
 	}
 #endif
@@ -1548,7 +1548,7 @@ namespace libtorrent {
 	{
 		char msg[1050];
 		std::snprintf(msg, sizeof(msg), "DHT immutable item %s [ %s ]"
-			, aux::to_hex(target.to_string()).c_str()
+			, aux::to_hex(target).c_str()
 			, item.to_string().c_str());
 		return msg;
 	}
@@ -1569,7 +1569,7 @@ namespace libtorrent {
 	{
 		char msg[1050];
 		std::snprintf(msg, sizeof(msg), "DHT mutable item (key=%s salt=%s seq=%" PRId64 " %s) [ %s ]"
-			, aux::to_hex(std::string(&key[0], 32)).c_str()
+			, aux::to_hex(key).c_str()
 			, salt.c_str()
 			, seq
 			, authoritative ? "auth" : "non-auth"
@@ -1604,8 +1604,8 @@ namespace libtorrent {
 		{
 			std::snprintf(msg, sizeof(msg), "DHT put complete (success=%d key=%s sig=%s salt=%s seq=%" PRId64 ")"
 				, num_success
-				, aux::to_hex(std::string(&public_key[0], 32)).c_str()
-				, aux::to_hex(std::string(&signature[0], 64)).c_str()
+				, aux::to_hex(public_key).c_str()
+				, aux::to_hex(signature).c_str()
 				, salt.c_str()
 				, seq);
 			return msg;
@@ -1613,7 +1613,7 @@ namespace libtorrent {
 
 		std::snprintf(msg, sizeof(msg), "DHT put commplete (success=%d hash=%s)"
 			, num_success
-			, aux::to_hex(target.to_string()).c_str());
+			, aux::to_hex(target).c_str());
 		return msg;
 	}
 
@@ -1645,10 +1645,10 @@ namespace libtorrent {
 		if (obfuscated_info_hash != info_hash)
 		{
 			std::snprintf(obf, sizeof(obf), " [obfuscated: %s]"
-			, aux::to_hex(obfuscated_info_hash.to_string()).c_str());
+			, aux::to_hex(obfuscated_info_hash).c_str());
 		}
 		std::snprintf(msg, sizeof(msg), "outgoing dht get_peers : %s%s -> %s"
-			, aux::to_hex(info_hash.to_string()).c_str()
+			, aux::to_hex(info_hash).c_str()
 			, obf
 			, print_endpoint(ip).c_str());
 		return msg;
@@ -1953,7 +1953,7 @@ namespace libtorrent {
 	std::string dht_get_peers_reply_alert::message() const
 	{
 		char ih_hex[41];
-		aux::to_hex(info_hash.data(), 20, ih_hex);
+		aux::to_hex(info_hash, ih_hex);
 		char msg[200];
 		std::snprintf(msg, sizeof(msg), "incoming dht get_peers reply: %s, peers %d", ih_hex, m_num_peers);
 		return msg;
diff --git a/src/bt_peer_connection.cpp b/src/bt_peer_connection.cpp
index c0765432a..8687edcc1 100644
--- a/src/bt_peer_connection.cpp
+++ b/src/bt_peer_connection.cpp
@@ -818,14 +818,14 @@ namespace libtorrent
 #ifndef TORRENT_DISABLE_LOGGING
 		{
 			char hex_pid[41];
-			aux::to_hex(m_our_peer_id.data(), 20, hex_pid);
+			aux::to_hex(m_our_peer_id, hex_pid);
 			hex_pid[40] = 0;
 			peer_log(peer_log_alert::outgoing, "HANDSHAKE"
 				, "sent peer_id: %s client: %s"
 				, hex_pid, identify_client(m_our_peer_id).c_str());
 		}
 		peer_log(peer_log_alert::outgoing_message, "HANDSHAKE"
-			, "ih: %s", aux::to_hex(ih.to_string()).c_str());
+			, "ih: %s", aux::to_hex(ih).c_str());
 #endif
 		send_buffer(handshake, sizeof(handshake));
 	}
@@ -3262,7 +3262,7 @@ namespace libtorrent
 #ifndef TORRENT_DISABLE_LOGGING
 			{
 				char hex_pid[41];
-				aux::to_hex(recv_buffer.begin(), 20, hex_pid);
+				aux::to_hex({recv_buffer.data(), 20}, hex_pid);
 				hex_pid[40] = 0;
 				char ascii_pid[21];
 				ascii_pid[20] = 0;
diff --git a/src/hex.cpp b/src/hex.cpp
index 200ac2ac8..bc0ef7b29 100644
--- a/src/hex.cpp
+++ b/src/hex.cpp
@@ -45,27 +45,27 @@ namespace libtorrent
 		return -1;
 	}
 
-	bool is_hex(char const *in, int len)
+	bool is_hex(span<char const> in)
 	{
-		for (char const* end = in + len; in < end; ++in)
+		for (char const c : in)
 		{
-			int t = hex_to_int(*in);
+			int const t = hex_to_int(c);
 			if (t == -1) return false;
 		}
 		return true;
 	}
 
-	bool from_hex(char const *in, int len, char* out)
+	bool from_hex(span<char const> in, char* out)
 	{
-		for (char const* end = in + len; in < end; ++in, ++out)
+		for (auto i = in.begin(), end = in.end(); i != end; ++i, ++out)
 		{
-			int t = aux::hex_to_int(*in);
-			if (t == -1) return false;
-			*out = t << 4;
-			++in;
-			t = aux::hex_to_int(*in);
-			if (t == -1) return false;
-			*out |= t & 15;
+			int const t1 = aux::hex_to_int(*i);
+			if (t1 == -1) return false;
+			*out = t1 << 4;
+			++i;
+			int const t2 = aux::hex_to_int(*i);
+			if (t2 == -1) return false;
+			*out |= t2 & 15;
 		}
 		return true;
 	}
@@ -74,23 +74,25 @@ namespace libtorrent
 
 	char const hex_chars[] = "0123456789abcdef";
 
-	std::string to_hex(std::string const& s)
+	std::string to_hex(span<char const> s)
 	{
 		std::string ret;
-		for (std::string::const_iterator i = s.begin(); i != s.end(); ++i)
+		ret.resize(s.size() * 2);
+		int idx = 0;
+		for (char const i : s)
 		{
-			ret += hex_chars[std::uint8_t(*i) >> 4];
-			ret += hex_chars[std::uint8_t(*i) & 0xf];
+			ret[idx++] = hex_chars[std::uint8_t(i) >> 4];
+			ret[idx++] = hex_chars[std::uint8_t(i) & 0xf];
 		}
 		return ret;
 	}
 
-	void to_hex(char const *in, int len, char* out)
+	void to_hex(span<char const> in, char* out)
 	{
-		for (char const* end = in + len; in < end; ++in)
+		for (char const i : in)
 		{
-			*out++ = hex_chars[std::uint8_t(*in) >> 4];
-			*out++ = hex_chars[std::uint8_t(*in) & 0xf];
+			*out++ = hex_chars[std::uint8_t(i) >> 4];
+			*out++ = hex_chars[std::uint8_t(i) & 0xf];
 		}
 		*out = '\0';
 	}
diff --git a/src/http_seed_connection.cpp b/src/http_seed_connection.cpp
index 3ed0fbc62..56e49975d 100644
--- a/src/http_seed_connection.cpp
+++ b/src/http_seed_connection.cpp
@@ -365,7 +365,7 @@ namespace libtorrent
 				std::int64_t chunk_size = 0;
 				span<char const> chunk_start(recv_buffer.begin() + m_chunk_pos, int(recv_buffer.size()) - m_chunk_pos);
 				TORRENT_ASSERT(chunk_start[0] == '\r'
-					|| aux::is_hex(chunk_start.data(), 1));
+					|| aux::is_hex(chunk_start[0]));
 				bool ret = m_parser.parse_chunk_header(chunk_start, &chunk_size, &header_size);
 				if (!ret)
 				{
diff --git a/src/i2p_stream.cpp b/src/i2p_stream.cpp
index a15785fe7..1d490fcd7 100644
--- a/src/i2p_stream.cpp
+++ b/src/i2p_stream.cpp
@@ -133,7 +133,7 @@ namespace libtorrent
 		char tmp[20];
 		std::generate(tmp, tmp + sizeof(tmp), &std::rand);
 		m_session_id.resize(sizeof(tmp)*2);
-		aux::to_hex(tmp, 20, &m_session_id[0]);
+		aux::to_hex(tmp, &m_session_id[0]);
 
 		m_sam_socket.reset(new i2p_stream(m_io_service));
 		m_sam_socket->set_proxy(m_hostname, m_port);
diff --git a/src/kademlia/dht_tracker.cpp b/src/kademlia/dht_tracker.cpp
index 3669802c7..730232d02 100644
--- a/src/kademlia/dht_tracker.cpp
+++ b/src/kademlia/dht_tracker.cpp
@@ -145,10 +145,10 @@ namespace libtorrent { namespace dht
 
 #ifndef TORRENT_DISABLE_LOGGING
 		m_log->log(dht_logger::tracker, "starting IPv4 DHT tracker with node id: %s"
-			, aux::to_hex(m_dht.nid().to_string()).c_str());
+			, aux::to_hex(m_dht.nid()).c_str());
 	#if TORRENT_USE_IPV6
 		m_log->log(dht_logger::tracker, "starting IPv6 DHT tracker with node id: %s"
-			, aux::to_hex(m_dht6.nid().to_string()).c_str());
+			, aux::to_hex(m_dht6.nid()).c_str());
 	#endif
 #endif
 	}
diff --git a/src/kademlia/find_data.cpp b/src/kademlia/find_data.cpp
index 94d7cbfad..1718db604 100644
--- a/src/kademlia/find_data.cpp
+++ b/src/kademlia/find_data.cpp
@@ -115,7 +115,7 @@ void find_data::got_write_token(node_id const& n, std::string const& write_token
 	get_node().observer()->log(dht_logger::traversal
 		, "[%p] adding write token '%s' under id '%s'"
 		, static_cast<void*>(this), aux::to_hex(write_token).c_str()
-		, aux::to_hex(n.to_string()).c_str());
+		, aux::to_hex(n).c_str());
 #endif
 	m_write_tokens[n] = write_token;
 }
diff --git a/src/kademlia/get_peers.cpp b/src/kademlia/get_peers.cpp
index c34871f8b..cbd58b224 100644
--- a/src/kademlia/get_peers.cpp
+++ b/src/kademlia/get_peers.cpp
@@ -72,7 +72,7 @@ void get_peers_observer::reply(msg const& m)
 			char const* end = peers + n.list_at(0).string_length();
 
 #ifndef TORRENT_DISABLE_LOGGING
-			bdecode_node id = r.dict_find_string("id");
+			bdecode_node const id = r.dict_find_string("id");
 			if (id && id.string_length() == 20)
 			{
 				get_observer()->log(dht_logger::traversal, "[%p] PEERS "
@@ -81,7 +81,7 @@ void get_peers_observer::reply(msg const& m)
 					, algorithm()->invoke_count()
 					, algorithm()->branch_factor()
 					, print_endpoint(m.addr).c_str()
-					, aux::to_hex(id.string_value()).c_str()
+					, aux::to_hex({id.string_ptr(), size_t(id.string_length())}).c_str()
 					, distance_exp(algorithm()->target(), node_id(id.string_ptr()))
 					, int((end - peers) / 6));
 			}
@@ -94,7 +94,7 @@ void get_peers_observer::reply(msg const& m)
 			// assume it's uTorrent/libtorrent format
 			read_endpoint_list<tcp::endpoint>(n, peer_list);
 #ifndef TORRENT_DISABLE_LOGGING
-			bdecode_node id = r.dict_find_string("id");
+			bdecode_node const id = r.dict_find_string("id");
 			if (id && id.string_length() == 20)
 			{
 				get_observer()->log(dht_logger::traversal, "[%p] PEERS "
@@ -103,7 +103,7 @@ void get_peers_observer::reply(msg const& m)
 					, algorithm()->invoke_count()
 					, algorithm()->branch_factor()
 					, print_endpoint(m.addr).c_str()
-					, aux::to_hex(id.string_value()).c_str()
+					, aux::to_hex({id.string_ptr(), size_t(id.string_length())}).c_str()
 					, distance_exp(algorithm()->target(), node_id(id.string_ptr()))
 					, int(n.list_size()));
 			}
diff --git a/src/kademlia/node.cpp b/src/kademlia/node.cpp
index b2c0eb471..fdf47d47d 100644
--- a/src/kademlia/node.cpp
+++ b/src/kademlia/node.cpp
@@ -361,7 +361,7 @@ namespace
 		if (node.observer())
 		{
 			char hex_ih[41];
-			aux::to_hex(ih.data(), 20, hex_ih);
+			aux::to_hex(ih, hex_ih);
 			node.observer()->log(dht_logger::node, "sending announce_peer [ ih: %s "
 				" p: %d nodes: %d ]", hex_ih, listen_port, int(v.size()));
 		}
@@ -451,7 +451,7 @@ void node::announce(sha1_hash const& info_hash, int listen_port, int flags
 	if (m_observer)
 	{
 		char hex_ih[41];
-		aux::to_hex(info_hash.data(), 20, hex_ih);
+		aux::to_hex(info_hash, hex_ih);
 		m_observer->log(dht_logger::node, "announcing [ ih: %s p: %d ]"
 			, hex_ih, listen_port);
 	}
@@ -485,7 +485,7 @@ void node::get_item(sha1_hash const& target
 	if (m_observer)
 	{
 		char hex_target[41];
-		aux::to_hex(target.data(), 20, hex_target);
+		aux::to_hex(target, hex_target);
 		m_observer->log(dht_logger::node, "starting get for [ hash: %s ]"
 			, hex_target);
 	}
@@ -503,7 +503,7 @@ void node::get_item(public_key const& pk, std::string const& salt
 	if (m_observer)
 	{
 		char hex_key[65];
-		aux::to_hex(pk.bytes.data(), 32, hex_key);
+		aux::to_hex(pk.bytes, hex_key);
 		m_observer->log(dht_logger::node, "starting get for [ key: %s ]", hex_key);
 	}
 #endif
@@ -542,7 +542,7 @@ void node::put_item(sha1_hash const& target, entry const& data, boost::function<
 	if (m_observer)
 	{
 		char hex_target[41];
-		aux::to_hex(target.data(), 20, hex_target);
+		aux::to_hex(target, hex_target);
 		m_observer->log(dht_logger::node, "starting get for [ hash: %s ]"
 			, hex_target);
 	}
@@ -568,7 +568,7 @@ void node::put_item(public_key const& pk, std::string const& salt
 	if (m_observer)
 	{
 		char hex_key[65];
-		aux::to_hex(pk.bytes.data(), 32, hex_key);
+		aux::to_hex(pk.bytes, hex_key);
 		m_observer->log(dht_logger::node, "starting get for [ key: %s ]", hex_key);
 	}
 	#endif
@@ -1028,9 +1028,9 @@ void node::incoming_request(msg const& m, entry& e)
 
 //		std::fprintf(stderr, "%s PUT target: %s salt: %s key: %s\n"
 //			, mutable_put ? "mutable":"immutable"
-//			, aux::to_hex(target.to_string()).c_str()
+//			, aux::to_hex(target).c_str()
 //			, salt.second > 0 ? std::string(salt.first, salt.second).c_str() : ""
-//			, pk ? aux::to_hex(std::string(pk, 32)).c_str() : "");
+//			, pk ? aux::to_hex(pk).c_str() : "");
 
 		// verify the write-token. tokens are only valid to write to
 		// specific target hashes. it must match the one we got a "get" for
@@ -1128,7 +1128,7 @@ void node::incoming_request(msg const& m, entry& e)
 
 //		std::fprintf(stderr, "%s GET target: %s\n"
 //			, msg_keys[1] ? "mutable":"immutable"
-//			, aux::to_hex(target.to_string()).c_str());
+//			, aux::to_hex(target).c_str());
 
 		reply["token"] = generate_token(m.addr, sha1_hash(msg_keys[1].string_ptr()));
 
diff --git a/src/kademlia/routing_table.cpp b/src/kademlia/routing_table.cpp
index dc7a3febf..1c7e2c480 100644
--- a/src/kademlia/routing_table.cpp
+++ b/src/kademlia/routing_table.cpp
@@ -256,7 +256,7 @@ void routing_table::print_state(std::ostream& os) const
 		"number of nodes per bucket:\n"
 		, m_bucket_size
 		, num_global_nodes()
-		, aux::to_hex(m_id.to_string()).c_str());
+		, aux::to_hex(m_id).c_str());
 	if (cursor > buf.size() - 500) buf.resize(buf.size() * 3 / 2);
 
 	int idx = 0;
@@ -318,7 +318,7 @@ void routing_table::print_state(std::ostream& os) const
 			cursor += std::snprintf(&buf[cursor], buf.size() - cursor
 				, " prefix: %2x id: %s"
 				, ((id[0] & top_mask) >> mask_shift)
-				, aux::to_hex(j->id.to_string()).c_str());
+				, aux::to_hex(j->id).c_str());
 
 			if (j->rtt == 0xffff)
 			{
@@ -1000,7 +1000,7 @@ ip_ok:
 			if (m_log)
 			{
 				char hex_id[41];
-				aux::to_hex(e.id.data(), int(e.id.size()), hex_id);
+				aux::to_hex(e.id, hex_id);
 				m_log->log(dht_logger::routing_table, "replacing node with higher RTT: %s %s"
 					, hex_id, print_address(e.addr()).c_str());
 			}
diff --git a/src/kademlia/traversal_algorithm.cpp b/src/kademlia/traversal_algorithm.cpp
index eead62700..c5269ea2a 100644
--- a/src/kademlia/traversal_algorithm.cpp
+++ b/src/kademlia/traversal_algorithm.cpp
@@ -100,7 +100,7 @@ traversal_algorithm::traversal_algorithm(
 	if (get_node().observer())
 	{
 		char hex_target[41];
-		aux::to_hex(reinterpret_cast<char const*>(&target[0]), 20, hex_target);
+		aux::to_hex(target, hex_target);
 		get_node().observer()->log(dht_logger::traversal, "[%p] NEW target: %s k: %d"
 			, static_cast<void*>(this), hex_target, int(m_node.m_table.bucket_size()));
 	}
@@ -181,7 +181,7 @@ void traversal_algorithm::add_entry(node_id const& id, udp::endpoint addr, unsig
 			if (get_node().observer())
 			{
 				char hex_id[41];
-				aux::to_hex(reinterpret_cast<char const*>(&o->id()[0]), 20, hex_id);
+				aux::to_hex(o->id(), hex_id);
 				get_node().observer()->log(dht_logger::traversal
 					, "[%p] traversal DUPLICATE node. id: %s addr: %s type: %s"
 					, static_cast<void*>(this), hex_id, print_address(o->target_addr()).c_str(), name());
@@ -200,7 +200,7 @@ void traversal_algorithm::add_entry(node_id const& id, udp::endpoint addr, unsig
 		if (get_node().observer())
 		{
 			char hex_id[41];
-			aux::to_hex(reinterpret_cast<char const*>(&id[0]), 20, hex_id);
+			aux::to_hex(id, hex_id);
 			get_node().observer()->log(dht_logger::traversal
 				, "[%p] ADD id: %s addr: %s distance: %d invoke-count: %d type: %s"
 				, static_cast<void*>(this), hex_id, print_endpoint(addr).c_str()
@@ -331,7 +331,7 @@ void traversal_algorithm::failed(observer_ptr o, int flags)
 		if (get_node().observer())
 		{
 			char hex_id[41];
-			aux::to_hex(reinterpret_cast<char const*>(&o->id()[0]), 20, hex_id);
+			aux::to_hex(o->id(), hex_id);
 			get_node().observer()->log(dht_logger::traversal
 				, "[%p] 1ST_TIMEOUT id: %s distance: %d addr: %s branch-factor: %d "
 				"invoke-count: %d type: %s"
@@ -353,7 +353,7 @@ void traversal_algorithm::failed(observer_ptr o, int flags)
 		if (get_node().observer())
 		{
 			char hex_id[41];
-			aux::to_hex(reinterpret_cast<char const*>(&o->id()[0]), 20, hex_id);
+			aux::to_hex(o->id(), hex_id);
 			get_node().observer()->log(dht_logger::traversal
 				, "[%p] TIMEOUT id: %s distance: %d addr: %s branch-factor: %d "
 				"invoke-count: %d type: %s"
@@ -401,7 +401,7 @@ void traversal_algorithm::done()
 		{
 			TORRENT_ASSERT(o->flags & observer::flag_queried);
 			char hex_id[41];
-			aux::to_hex(reinterpret_cast<char const*>(&o->id()[0]), 20, hex_id);
+			aux::to_hex(o->id(), hex_id);
 			get_node().observer()->log(dht_logger::traversal
 				, "[%p] id: %s distance: %d addr: %s"
 				, static_cast<void*>(this), hex_id, closest_target
@@ -481,7 +481,7 @@ bool traversal_algorithm::add_requests()
 		if (get_node().observer())
 		{
 			char hex_id[41];
-			aux::to_hex(reinterpret_cast<char const*>(&o->id()[0]), 20, hex_id);
+			aux::to_hex(o->id(), hex_id);
 			get_node().observer()->log(dht_logger::traversal
 				, "[%p] INVOKE nodes-left: %d top-invoke-count: %d "
 				"invoke-count: %d branch-factor: %d "
@@ -589,7 +589,7 @@ void traversal_observer::reply(msg const& m)
 	{
 		bdecode_node nid = r.dict_find_string("id");
 		char hex_id[41];
-		aux::to_hex(nid.string_ptr(), 20, hex_id);
+		aux::to_hex({nid.string_ptr(), 20}, hex_id);
 		get_observer()->log(dht_logger::traversal
 			, "[%p] RESPONSE id: %s invoke-count: %d addr: %s type: %s"
 			, static_cast<void*>(algorithm()), hex_id, algorithm()->invoke_count()
diff --git a/src/lsd.cpp b/src/lsd.cpp
index 976067afc..29d479831 100644
--- a/src/lsd.cpp
+++ b/src/lsd.cpp
@@ -142,7 +142,7 @@ void lsd::announce_impl(sha1_hash const& ih, int const listen_port
 #endif
 
 	char ih_hex[41];
-	aux::to_hex(ih.data(), 20, ih_hex);
+	aux::to_hex(ih, ih_hex);
 	char msg[200];
 
 #ifndef TORRENT_DISABLE_LOGGING
@@ -278,7 +278,7 @@ void lsd::on_announce(udp::endpoint const& from, char* buf
 		}
 
 		sha1_hash ih(nullptr);
-		aux::from_hex(ih_str.c_str(), 40, ih.data());
+		aux::from_hex(ih_str, ih.data());
 
 		if (!ih.is_all_zeros() && port != 0)
 		{
diff --git a/src/magnet_uri.cpp b/src/magnet_uri.cpp
index 671e5c716..e0e5c186f 100644
--- a/src/magnet_uri.cpp
+++ b/src/magnet_uri.cpp
@@ -50,7 +50,7 @@ namespace libtorrent
 		std::string ret;
 		sha1_hash const& ih = handle.info_hash();
 		ret += "magnet:?xt=urn:btih:";
-		ret += aux::to_hex(ih.to_string());
+		ret += aux::to_hex(ih);
 
 		torrent_status st = handle.status(torrent_handle::query_name);
 		if (!st.name.empty())
@@ -82,7 +82,7 @@ namespace libtorrent
 		std::string ret;
 		sha1_hash const& ih = info.info_hash();
 		ret += "magnet:?xt=urn:btih:";
-		ret += aux::to_hex(ih.to_string());
+		ret += aux::to_hex(ih);
 
 		std::string const& name = info.name();
 
@@ -158,7 +158,7 @@ namespace libtorrent
 
 		if (btih.compare(0, 9, "urn:btih:") != 0) return torrent_handle();
 
-		if (btih.size() == 40 + 9) aux::from_hex(&btih[9], 40, params.info_hash.data());
+		if (btih.size() == 40 + 9) aux::from_hex({&btih[9], 40}, params.info_hash.data());
 		else params.info_hash.assign(base32decode(btih.substr(9)));
 
 		return ses.add_torrent(params);
@@ -265,7 +265,7 @@ namespace libtorrent
 #endif
 
 		sha1_hash info_hash;
-		if (btih.size() == 40 + 9) aux::from_hex(&btih[9], 40, info_hash.data());
+		if (btih.size() == 40 + 9) aux::from_hex({&btih[9], 40}, info_hash.data());
 		else if (btih.size() == 32 + 9)
 		{
 			std::string ih = base32decode(btih.substr(9));
diff --git a/src/peer_connection.cpp b/src/peer_connection.cpp
index 21bea3f1a..34ad7253b 100644
--- a/src/peer_connection.cpp
+++ b/src/peer_connection.cpp
@@ -1193,7 +1193,7 @@ namespace libtorrent
 #ifndef TORRENT_DISABLE_LOGGING
 			if (t)
 				peer_log(peer_log_alert::info, "ATTACH"
-					, "Delay loaded torrent: %s:", aux::to_hex(ih.to_string()).c_str());
+					, "Delay loaded torrent: %s:", aux::to_hex(ih).c_str());
 #endif
 		}
 
@@ -1203,7 +1203,7 @@ namespace libtorrent
 #ifndef TORRENT_DISABLE_LOGGING
 			peer_log(peer_log_alert::info, "ATTACH"
 				, "couldn't find a torrent with the given info_hash: %s torrents:"
-				, aux::to_hex(ih.to_string()).c_str());
+				, aux::to_hex(ih).c_str());
 #endif
 
 #ifndef TORRENT_DISABLE_DHT
diff --git a/src/session_impl.cpp b/src/session_impl.cpp
index e2ca98b94..90bee7188 100644
--- a/src/session_impl.cpp
+++ b/src/session_impl.cpp
@@ -6926,7 +6926,7 @@ namespace aux {
 			i != resp.peers.end(); ++i)
 			{
 				debug_log("  %16s %5d %s %s", i->hostname.c_str(), i->port
-					, i->pid.is_all_zeros()?"":to_hex(i->pid.to_string()).c_str()
+					, i->pid.is_all_zeros()?"":to_hex(i->pid).c_str()
 					, identify_client(i->pid).c_str());
 			}
 			for (std::vector<ipv4_peer_entry>::const_iterator i = resp.peers4.begin();
diff --git a/src/sha1_hash.cpp b/src/sha1_hash.cpp
index 786c49581..5b7e7c927 100644
--- a/src/sha1_hash.cpp
+++ b/src/sha1_hash.cpp
@@ -47,7 +47,7 @@ namespace libtorrent
 	std::ostream& operator<<(std::ostream& os, sha1_hash const& peer)
 	{
 		char out[sha1_hash::size() * 2 + 1];
-		aux::to_hex(peer.data(), int(sha1_hash::size()), out);
+		aux::to_hex(peer, out);
 		return os << out;
 	}
 
@@ -56,7 +56,7 @@ namespace libtorrent
 	{
 		char hex[sha1_hash::size() * 2];
 		is.read(hex, sha1_hash::size() * 2);
-		if (!aux::from_hex(hex, int(sha1_hash::size()) * 2, peer.data()))
+		if (!aux::from_hex(hex, peer.data()))
 			is.setstate(std::ios_base::failbit);
 		return is;
 	}
diff --git a/src/smart_ban.cpp b/src/smart_ban.cpp
index a8784d770..be9dcbc77 100644
--- a/src/smart_ban.cpp
+++ b/src/smart_ban.cpp
@@ -227,8 +227,8 @@ namespace
 					m_torrent.debug_log(" BANNING PEER [ p: %d | b: %d | c: %s"
 						" | hash1: %s | hash2: %s | ip: %s ]"
 						, b.piece_index, b.block_index, client
-						, aux::to_hex(i->second.digest.to_string()).c_str()
-						, aux::to_hex(e.digest.to_string()).c_str()
+						, aux::to_hex(i->second.digest).c_str()
+						, aux::to_hex(e.digest).c_str()
 						, print_endpoint(p->ip()).c_str());
 #endif
 					m_torrent.ban_peer(p);
@@ -253,7 +253,7 @@ namespace
 			m_torrent.debug_log(" STORE BLOCK CRC [ p: %d | b: %d | c: %s"
 				" | digest: %s | ip: %s ]"
 				, b.piece_index, b.block_index, client
-				, aux::to_hex(e.digest.to_string()).c_str()
+				, aux::to_hex(e.digest).c_str()
 				, print_address(p->ip().address()).c_str());
 #endif
 		}
@@ -297,8 +297,8 @@ namespace
 			m_torrent.debug_log(" BANNING PEER [ p: %d | b: %d | c: %s"
 				" | ok_digest: %s | bad_digest: %s | ip: %s ]"
 				, b.first.piece_index, b.first.block_index, client
-				, aux::to_hex(ok_digest.to_string()).c_str()
-				, aux::to_hex(b.second.digest.to_string()).c_str()
+				, aux::to_hex(ok_digest).c_str()
+				, aux::to_hex(b.second.digest).c_str()
 				, print_address(p->ip().address()).c_str());
 #endif
 			m_torrent.ban_peer(p);
diff --git a/src/storage.cpp b/src/storage.cpp
index e1e0d7b95..9a7b4e1ac 100644
--- a/src/storage.cpp
+++ b/src/storage.cpp
@@ -409,7 +409,7 @@ namespace libtorrent
 		TORRENT_ASSERT(m_files.num_files() > 0);
 		m_save_path = complete(params.path);
 		m_part_file_name = "." + (params.info
-			? aux::to_hex(params.info->info_hash().to_string())
+			? aux::to_hex(params.info->info_hash())
 			: params.files->name()) + ".parts";
 	}
 
diff --git a/src/torrent.cpp b/src/torrent.cpp
index d30573b1d..b9e03dffe 100644
--- a/src/torrent.cpp
+++ b/src/torrent.cpp
@@ -3309,7 +3309,7 @@ namespace libtorrent
 			i != resp.peers.end(); ++i)
 		{
 			debug_log("  %16s %5d %s %s", i->hostname.c_str(), i->port
-				, i->pid.is_all_zeros()?"":aux::to_hex(i->pid.to_string()).c_str()
+				, i->pid.is_all_zeros()?"":aux::to_hex(i->pid).c_str()
 				, identify_client(i->pid).c_str());
 		}
 		for (std::vector<ipv4_peer_entry>::const_iterator i = resp.peers4.begin();
@@ -6918,7 +6918,7 @@ namespace libtorrent
 			if (is_ssl_torrent())
 			{
 				// for ssl sockets, set the hostname
-				std::string host_name = aux::to_hex(m_torrent_file->info_hash().to_string());
+				std::string host_name = aux::to_hex(m_torrent_file->info_hash());
 
 #define CASE(t) case socket_type_int_impl<ssl_stream<t> >::value: \
 	s->get<ssl_stream<t> >()->set_host_name(host_name); break;
diff --git a/src/torrent_info.cpp b/src/torrent_info.cpp
index b9c9a87e2..2505c0a48 100644
--- a/src/torrent_info.cpp
+++ b/src/torrent_info.cpp
@@ -1092,7 +1092,7 @@ namespace libtorrent
 		std::string name;
 		sanitize_append_path_element(name, name_ent.string_ptr()
 			, name_ent.string_length());
-		if (name.empty()) name = aux::to_hex(m_info_hash.to_string());
+		if (name.empty()) name = aux::to_hex(m_info_hash);
 
 		// extract file list
 		bdecode_node files_node = info.dict_find_list("files");
diff --git a/src/udp_tracker_connection.cpp b/src/udp_tracker_connection.cpp
index b4991a93c..ec2dbca07 100644
--- a/src/udp_tracker_connection.cpp
+++ b/src/udp_tracker_connection.cpp
@@ -531,7 +531,7 @@ namespace libtorrent
 		if (cb)
 		{
 			char hex_ih[41];
-			aux::to_hex(tracker_req().info_hash.data(), 20, hex_ih);
+			aux::to_hex(tracker_req().info_hash, hex_ih);
 			cb->debug_log("==> UDP_TRACKER_CONNECT [ to: %s ih: %s]"
 				, m_hostname.empty()
 					? print_endpoint(m_target).c_str()
@@ -763,7 +763,7 @@ namespace libtorrent
 		if (cb)
 		{
 			char hex_ih[41];
-			aux::to_hex(req.info_hash.data(), 20, hex_ih);
+			aux::to_hex(req.info_hash, hex_ih);
 			cb->debug_log("==> UDP_TRACKER_ANNOUNCE [%s]", hex_ih);
 		}
 #endif
diff --git a/src/web_peer_connection.cpp b/src/web_peer_connection.cpp
index 8547e4da0..e35c700d4 100644
--- a/src/web_peer_connection.cpp
+++ b/src/web_peer_connection.cpp
@@ -829,7 +829,7 @@ void web_peer_connection::on_receive(error_code const& error
 				std::int64_t chunk_size = 0;
 				span<char const> chunk_start = recv_buffer.subspan(m_chunk_pos);
 				TORRENT_ASSERT(chunk_start[0] == '\r'
-					|| aux::is_hex(chunk_start.data(), 1));
+					|| aux::is_hex({chunk_start.data(), 1}));
 				bool const ret = m_parser.parse_chunk_header(chunk_start, &chunk_size, &header_size);
 				if (!ret)
 				{
diff --git a/test/setup_transfer.cpp b/test/setup_transfer.cpp
index edb078076..fd3c02ce5 100644
--- a/test/setup_transfer.cpp
+++ b/test/setup_transfer.cpp
@@ -836,7 +836,7 @@ setup_transfer(lt::session* ses1, lt::session* ses2, lt::session* ses3
 			remove_all(combine_path("tmp3" + suffix, "temporary"), ec);
 		}
 		char ih_hex[41];
-		aux::to_hex((char const*)&t->info_hash()[0], 20, ih_hex);
+		aux::to_hex(t->info_hash(), ih_hex);
 		std::fprintf(stderr, "generated torrent: %s tmp1%s/temporary\n", ih_hex, suffix.c_str());
 	}
 	else
diff --git a/test/test_checking.cpp b/test/test_checking.cpp
index c2fe9b20d..67eadfb49 100644
--- a/test/test_checking.cpp
+++ b/test/test_checking.cpp
@@ -117,7 +117,7 @@ void test_checking(int flags = read_only_files)
 	boost::shared_ptr<torrent_info> ti(new torrent_info(&buf[0], int(buf.size()), ec));
 
 	std::fprintf(stderr, "generated torrent: %s tmp1_checking/test_torrent_dir\n"
-		, aux::to_hex(ti->info_hash().to_string()).c_str());
+		, aux::to_hex(ti->info_hash()).c_str());
 
 	// truncate every file in half
 	if (flags & incomplete_files)
diff --git a/test/test_dht.cpp b/test/test_dht.cpp
index eed875fe0..6bd5ed0cc 100644
--- a/test/test_dht.cpp
+++ b/test/test_dht.cpp
@@ -66,15 +66,15 @@ namespace {
 sha1_hash to_hash(char const* s)
 {
 	sha1_hash ret;
-	aux::from_hex(s, 40, (char*)&ret[0]);
+	aux::from_hex({s, 40}, (char*)&ret[0]);
 	return ret;
 }
 
 void get_test_keypair(public_key& pk, secret_key& sk)
 {
-	aux::from_hex("77ff84905a91936367c01360803104f92432fcd904a43511876df5cdf3e7e548", 64, pk.bytes.data());
-	aux::from_hex("e06d3183d14159228433ed599221b80bd0a5ce8352e4bdf0262f76786ef1c74d"
-		"b7e7a9fea2c0eb269d61e3b38e450a22e754941ac78479d6c54e1faf6037881d", 128, sk.bytes.data());
+	aux::from_hex({"77ff84905a91936367c01360803104f92432fcd904a43511876df5cdf3e7e548", 64}, pk.bytes.data());
+	aux::from_hex({"e06d3183d14159228433ed599221b80bd0a5ce8352e4bdf0262f76786ef1c74d"
+		"b7e7a9fea2c0eb269d61e3b38e450a22e754941ac78479d6c54e1faf6037881d", 128}, sk.bytes.data());
 }
 
 sequence_number prev_seq(sequence_number s)
@@ -942,16 +942,17 @@ TORRENT_TEST(bloom_filter)
 	// these are test vectors from BEP 33
 	// http://www.bittorrent.org/beps/bep_0033.html
 	std::fprintf(stderr, "test.size: %f\n", test.size());
-	std::fprintf(stderr, "%s\n", aux::to_hex(test.to_string()).c_str());
+	std::string const bf_str = test.to_string();
+	std::fprintf(stderr, "%s\n", aux::to_hex(bf_str).c_str());
 	if (supports_ipv6())
 	{
 		TEST_CHECK(fabs(test.size() - 1224.93f) < 0.001);
-		TEST_CHECK(aux::to_hex(test.to_string()) == "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");
+		TEST_CHECK(aux::to_hex(bf_str) == "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");
 	}
 	else
 	{
 		TEST_CHECK(fabs(test.size() - 257.854f) < 0.001);
-		TEST_CHECK(aux::to_hex(test.to_string()) == "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");
+		TEST_CHECK(aux::to_hex(bf_str) == "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");
 	}
 }
 
@@ -1057,8 +1058,8 @@ void test_put(address(&rand_addr)())
 		ed25519_create_keypair((unsigned char*)pk.bytes.data()
 			, (unsigned char*)sk.bytes.data(), seed);
 		std::fprintf(stderr, "pub: %s priv: %s\n"
-			, aux::to_hex(std::string(pk.bytes.data(), public_key::len)).c_str()
-			, aux::to_hex(std::string(sk.bytes.data(), secret_key::len)).c_str());
+			, aux::to_hex(pk.bytes).c_str()
+			, aux::to_hex(sk.bytes).c_str());
 
 		std::string salt;
 		if (with_salt) salt = "foobar";
@@ -1068,7 +1069,7 @@ void test_put(address(&rand_addr)())
 		sha1_hash target_id = h.final();
 
 		std::fprintf(stderr, "target_id: %s\n"
-			, aux::to_hex(target_id.to_string()).c_str());
+			, aux::to_hex(target_id).c_str());
 
 		send_dht_request(t.dht_node, "get", t.source, &response
 			, msg_args().target(target_id));
@@ -1135,7 +1136,7 @@ void test_put(address(&rand_addr)())
 			, msg_args().target(target_id));
 
 		std::fprintf(stderr, "target_id: %s\n"
-			, aux::to_hex(target_id.to_string()).c_str());
+			, aux::to_hex(target_id).c_str());
 
 		key_desc_t const desc3[] =
 		{
@@ -1516,15 +1517,15 @@ void test_routing_table(address(&rand_addr)())
 
 	for (int i = 0; i < 5; ++i)
 	{
-		address a = addr4(ips[i]);
-		node_id id = generate_id_impl(a, rs[i]);
+		address const a = addr4(ips[i]);
+		node_id const id = generate_id_impl(a, rs[i]);
 		TEST_CHECK(id[0] == prefixes[i][0]);
 		TEST_CHECK(id[1] == prefixes[i][1]);
 		TEST_CHECK((id[2] & 0xf8) == (prefixes[i][2] & 0xf8));
 
 		TEST_CHECK(id[19] == rs[i]);
 		std::fprintf(stderr, "IP address: %s r: %d node ID: %s\n", ips[i]
-			, rs[i], aux::to_hex(id.to_string()).c_str());
+			, rs[i], aux::to_hex(id).c_str());
 	}
 }
 
@@ -2392,12 +2393,12 @@ TORRENT_TEST(signing_test1)
 	signature sig;
 	sign_mutable_item(test_content, empty_salt, sequence_number(1), pk, sk, sig);
 
-	TEST_EQUAL(aux::to_hex(std::string(sig.bytes.data(), signature::len))
+	TEST_EQUAL(aux::to_hex(sig.bytes)
 		, "305ac8aeb6c9c151fa120f120ea2cfb923564e11552d06a5d856091e5e853cff"
 		"1260d3f39e4999684aa92eb73ffd136e6f4f3ecbfda0ce53a1608ecd7ae21f01");
 
-	sha1_hash target_id = item_target_id(empty_salt, pk);
-	TEST_EQUAL(aux::to_hex(target_id.to_string()), "4a533d47ec9c7d95b1ad75f576cffc641853b750");
+	sha1_hash const target_id = item_target_id(empty_salt, pk);
+	TEST_EQUAL(aux::to_hex(target_id), "4a533d47ec9c7d95b1ad75f576cffc641853b750");
 }
 
 TORRENT_TEST(signing_test2)
@@ -2416,12 +2417,12 @@ TORRENT_TEST(signing_test2)
 	// test vector 2 (the keypair is the same as test 1)
 	sign_mutable_item(test_content, test_salt, sequence_number(1), pk, sk, sig);
 
-	TEST_EQUAL(aux::to_hex(std::string(sig.bytes.data(), signature::len))
+	TEST_EQUAL(aux::to_hex(sig.bytes)
 		, "6834284b6b24c3204eb2fea824d82f88883a3d95e8b4a21b8c0ded553d17d17d"
 		"df9a8a7104b1258f30bed3787e6cb896fca78c58f8e03b5f18f14951a87d9a08");
 
 	sha1_hash target_id = item_target_id(test_salt, pk);
-	TEST_EQUAL(aux::to_hex(target_id.to_string()), "411eba73b6f087ca51a3795d9c8c938d365e32c1");
+	TEST_EQUAL(aux::to_hex(target_id), "411eba73b6f087ca51a3795d9c8c938d365e32c1");
 }
 
 TORRENT_TEST(signing_test3)
@@ -2432,7 +2433,7 @@ TORRENT_TEST(signing_test3)
 	span<char const> test_content("12:Hello World!", 15);
 
 	sha1_hash target_id = item_target_id(test_content);
-	TEST_EQUAL(aux::to_hex(target_id.to_string()), "e5f96f6f38320f0f33959cb4d3d656452117aadb");
+	TEST_EQUAL(aux::to_hex(target_id), "e5f96f6f38320f0f33959cb4d3d656452117aadb");
 }
 
 // TODO: 2 split this up into smaller test cases
diff --git a/test/test_hasher.cpp b/test/test_hasher.cpp
index 9f1f4028d..beca7d3a1 100644
--- a/test/test_hasher.cpp
+++ b/test/test_hasher.cpp
@@ -70,7 +70,7 @@ TORRENT_TEST(hasher)
 			h.update(test_array[test], int(std::strlen(test_array[test])));
 
 		sha1_hash result;
-		aux::from_hex(result_array[test], 40, (char*)&result[0]);
+		aux::from_hex({result_array[test], 40}, (char*)&result[0]);
 		TEST_CHECK(result == h.final());
 	}
 }
diff --git a/test/test_magnet.cpp b/test/test_magnet.cpp
index 8f827c9ce..37c552129 100644
--- a/test/test_magnet.cpp
+++ b/test/test_magnet.cpp
@@ -177,7 +177,8 @@ TORRENT_TEST(magnet)
 		std::fprintf(stderr, "3: %s\n", trackers[2].url.c_str());
 	}
 
-	TEST_EQUAL(aux::to_hex(t.info_hash().to_string()), "cdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcd");
+	sha1_hash const ih = t.info_hash();
+	TEST_EQUAL(aux::to_hex(ih), "cdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcdcd");
 
 	p1 = s->abort();
 	s.reset(new lt::session());
diff --git a/test/test_primitives.cpp b/test/test_primitives.cpp
index 27ac90d35..2294ce07a 100644
--- a/test/test_primitives.cpp
+++ b/test/test_primitives.cpp
@@ -44,7 +44,7 @@ using namespace libtorrent;
 sha1_hash to_hash(char const* s)
 {
 	sha1_hash ret;
-	aux::from_hex(s, 40, (char*)&ret[0]);
+	aux::from_hex({s, 40}, (char*)&ret[0]);
 	return ret;
 }
 
diff --git a/test/test_read_piece.cpp b/test/test_read_piece.cpp
index f314ba0d9..983165d79 100644
--- a/test/test_read_piece.cpp
+++ b/test/test_read_piece.cpp
@@ -87,7 +87,7 @@ void test_read_piece(int flags)
 	boost::shared_ptr<torrent_info> ti(new torrent_info(&buf[0], int(buf.size()), ec));
 
 	std::fprintf(stderr, "generated torrent: %s tmp1_read_piece/test_torrent\n"
-		, aux::to_hex(ti->info_hash().to_string()).c_str());
+		, aux::to_hex(ti->info_hash()).c_str());
 
 	const int mask = alert::all_categories
 		& ~(alert::progress_notification
diff --git a/test/test_resolve_links.cpp b/test/test_resolve_links.cpp
index d5d14345a..3f17c97c8 100644
--- a/test/test_resolve_links.cpp
+++ b/test/test_resolve_links.cpp
@@ -121,8 +121,8 @@ TORRENT_TEST(resolve_links)
 			{
 				TORRENT_ASSERT(i < fs.num_files());
 				std::fprintf(stderr, "%s --> %s : %d\n", fs.file_name(i).c_str()
-					, links[i].ti ? aux::to_hex(links[i].ti->info_hash()
-						.to_string()).c_str() : "", links[i].file_idx);
+					, links[i].ti ? aux::to_hex(links[i].ti->info_hash()).c_str()
+					: "", links[i].file_idx);
 			}
 		}
 
diff --git a/test/test_sha1_hash.cpp b/test/test_sha1_hash.cpp
index 8d9932bd4..774cf5285 100644
--- a/test/test_sha1_hash.cpp
+++ b/test/test_sha1_hash.cpp
@@ -39,7 +39,7 @@ using namespace libtorrent;
 static sha1_hash to_hash(char const* s)
 {
 	sha1_hash ret;
-	aux::from_hex(s, 40, (char*)&ret[0]);
+	aux::from_hex({s, 40}, ret.data());
 	return ret;
 }
 
diff --git a/test/test_string.cpp b/test/test_string.cpp
index 21bc264e7..6cb5a22db 100644
--- a/test/test_string.cpp
+++ b/test/test_string.cpp
@@ -54,21 +54,21 @@ TORRENT_TEST(hex)
 {
 	static char const str[] = "0123456789012345678901234567890123456789";
 	char bin[20];
-	TEST_CHECK(aux::from_hex(str, 40, bin));
+	TEST_CHECK(aux::from_hex({str, 40}, bin));
 	char hex[41];
-	aux::to_hex(bin, 20, hex);
+	aux::to_hex(bin, hex);
 	TEST_CHECK(strcmp(hex, str) == 0);
 
-	TEST_CHECK(aux::to_hex("\x55\x73") == "5573");
-	TEST_CHECK(aux::to_hex("\xaB\xd0") == "abd0");
+	TEST_CHECK(aux::to_hex({"\x55\x73",2}) == "5573");
+	TEST_CHECK(aux::to_hex({"\xaB\xd0",2}) == "abd0");
 
 	static char const hex_chars[] = "0123456789abcdefABCDEF";
 
 	for (int i = 1; i < 255; ++i)
 	{
-		bool hex = strchr(hex_chars, i) != nullptr;
-		char c = i;
-		TEST_EQUAL(aux::is_hex(&c, 1), hex);
+		bool const hex = strchr(hex_chars, i) != nullptr;
+		char const c = i;
+		TEST_EQUAL(aux::is_hex(c), hex);
 	}
 
 	TEST_EQUAL(aux::hex_to_int('0'), 0);
diff --git a/test/test_torrent_info.cpp b/test/test_torrent_info.cpp
index 3778df647..6d1f2d973 100644
--- a/test/test_torrent_info.cpp
+++ b/test/test_torrent_info.cpp
@@ -717,9 +717,10 @@ TORRENT_TEST(parse_torrents)
 		file_storage const& fs = ti->files();
 		for (int i = 0; i < fs.num_files(); ++i)
 		{
-			int first = ti->map_file(i, 0, 0).piece;
-			int last = ti->map_file(i, (std::max)(fs.file_size(i)-1, std::int64_t(0)), 0).piece;
-			int flags = fs.file_flags(i);
+			int const first = ti->map_file(i, 0, 0).piece;
+			int const last = ti->map_file(i, (std::max)(fs.file_size(i)-1, std::int64_t(0)), 0).piece;
+			int const flags = fs.file_flags(i);
+			sha1_hash const ih = fs.hash(i);
 			std::fprintf(stderr, "  %11" PRId64 " %c%c%c%c [ %4d, %4d ] %7u %s %s %s%s\n"
 				, fs.file_size(i)
 				, (flags & file_storage::flag_pad_file)?'p':'-'
@@ -728,7 +729,7 @@ TORRENT_TEST(parse_torrents)
 				, (flags & file_storage::flag_symlink)?'l':'-'
 				, first, last
 				, std::uint32_t(fs.mtime(i))
-				, fs.hash(i) != sha1_hash(nullptr) ? aux::to_hex(fs.hash(i).to_string()).c_str() : ""
+				, ih != sha1_hash(nullptr) ? aux::to_hex(ih).c_str() : ""
 				, fs.file_path(i).c_str()
 				, flags & file_storage::flag_symlink ? "-> ": ""
 				, flags & file_storage::flag_symlink ? fs.symlink(i).c_str() : "");