give some magic numbers names

include/libtorrent/sha1_hash.hpp

@@ -38,6 +38,7 @@ POSSIBILITY OF SUCH DAMAGE.
 #include <string>
 #include <cstring>
 #include <array>
+#include <climits> // for CHAR_BIT
 
 #include "libtorrent/config.hpp"
 #include "libtorrent/assert.hpp"
@@ -72,7 +73,7 @@ namespace aux {
 	public:
 
 		// the size of the hash in bytes
-		static constexpr std::size_t size() noexcept { return N / 8; }
+		static constexpr std::size_t size() noexcept { return N / CHAR_BIT; }
 
 		// constructs an all-zero digest
 		digest32() noexcept { clear(); }
@@ -81,7 +82,7 @@ namespace aux {
 		digest32& operator=(digest32 const&) noexcept = default;
 
 		// returns an all-F digest. i.e. the maximum value
-		// representable by an N bit number (N/8 bytes). This is
+		// representable by an N bit number (N/CHAR_BIT bytes). This is
 		// a static member function.
 		static digest32 (max)() noexcept
 		{
@@ -91,7 +92,7 @@ namespace aux {
 		}
 
 		// returns an all-zero digest. i.e. the minimum value
-		// representable by an N bit number (N/8 bytes). This is
+		// representable by an N bit number (N/CHAR_BIT bytes). This is
 		// a static member function.
 		static digest32 (min)() noexcept
 		{
@@ -100,8 +101,8 @@ namespace aux {
 			return ret;
 		}
 
-		// copies N/8 bytes from the pointer provided, into the digest.
-		// The passed in string MUST be at least N/8 bytes. 0-terminators
+		// copies N/CHAR_BIT bytes from the pointer provided, into the digest.
+		// The passed in string MUST be at least N/CHAR_BIT bytes. 0-terminators
 		// are ignored, ``s`` is treated like a raw memory buffer.
 		explicit digest32(char const* s) noexcept
 		{
@@ -121,7 +122,7 @@ namespace aux {
 		}
 		void assign(span<char const> s) noexcept
 		{
-			TORRENT_ASSERT(s.size() >= N / 8);
+			TORRENT_ASSERT(s.size() >= N / CHAR_BIT);
 			std::size_t const sl = s.size() < size() ? s.size() : size();
 			std::memcpy(m_number.data(), s.data(), sl);
 		}
@@ -256,8 +257,8 @@ namespace aux {
 		iterator end()
 		{ return reinterpret_cast<std::uint8_t*>(m_number.data()) + size(); }
 
-		// return a copy of the N/8 bytes representing the digest as a std::string.
-		// It's still a binary string with N/8 binary characters.
+		// return a copy of the N/CHAR_BIT bytes representing the digest as a std::string.
+		// It's still a binary string with N/CHAR_BIT binary characters.
 		std::string to_string() const
 		{
 			return std::string(reinterpret_cast<char const*>(m_number.data()), size());

src/create_torrent.cpp

@@ -296,11 +296,14 @@ namespace {
 
 		settings_pack sett;
 		sett.set_int(settings_pack::cache_size, 0);
-		sett.set_int(settings_pack::aio_threads, 3);
+		int const num_threads = disk_io_thread::hasher_thread_divisor - 1;
+		int const jobs_per_thread = 4;
+		sett.set_int(settings_pack::aio_threads, num_threads);
 
 		disk_thread.set_settings(&sett);
 
-		int const piece_read_ahead = std::max(12, 16 * 1024 * 1024 / t.piece_length());
+		int const piece_read_ahead = std::max(num_threads * jobs_per_thread
+			, default_block_size / t.piece_length());
 
 		hash_state st = { t, std::move(storage), disk_thread, piece_index_t(0), piece_index_t(0), f, ec };
 		for (piece_index_t i(0); i < piece_index_t(piece_read_ahead); ++i)

src/read_resume_data.cpp

@@ -86,7 +86,7 @@ namespace {
 		}
 
 		auto info_hash = rd.dict_find_string_value("info-hash");
-		if (info_hash.size() != 20)
+		if (info_hash.size() != sha1_hash::size())
 		{
 			ec = errors::missing_info_hash;
 			return ret;
@@ -253,11 +253,11 @@ namespace {
 		}
 
 		bdecode_node const mt = rd.dict_find_string("merkle tree");
-		if (mt && mt.string_length() >= 20)
+		if (mt && mt.string_length() >= int(sha1_hash::size()))
 		{
-			ret.merkle_tree.resize(aux::numeric_cast<std::size_t>(mt.string_length() / 20));
+			ret.merkle_tree.resize(aux::numeric_cast<std::size_t>(mt.string_length()) / sha1_hash::size());
 			std::memcpy(ret.merkle_tree.data(), mt.string_ptr()
-				, ret.merkle_tree.size() * 20);
+				, ret.merkle_tree.size() * sha1_hash::size());
 		}
 
 		// some sanity checking. Maybe we shouldn't be in seed mode anymore
@@ -292,11 +292,15 @@ namespace {
 			}
 		}
 
+#if TORRENT_USE_IPV6
+		int const v6_size = 18;
+#endif
+		int const v4_size = 6;
 		using namespace libtorrent::detail; // for read_*_endpoint()
 		if (bdecode_node const peers_entry = rd.dict_find_string("peers"))
 		{
 			char const* ptr = peers_entry.string_ptr();
-			for (int i = 5; i < peers_entry.string_length(); i += 6)
+			for (int i = v4_size - 1; i < peers_entry.string_length(); i += v4_size)
 				ret.peers.push_back(read_v4_endpoint<tcp::endpoint>(ptr));
 		}
 
@@ -304,7 +308,7 @@ namespace {
 		if (bdecode_node const peers_entry = rd.dict_find_string("peers6"))
 		{
 			char const* ptr = peers_entry.string_ptr();
-			for (int i = 17; i < peers_entry.string_length(); i += 18)
+			for (int i = v6_size - 1; i < peers_entry.string_length(); i += v6_size)
 				ret.peers.push_back(read_v6_endpoint<tcp::endpoint>(ptr));
 		}
 #endif
@@ -312,7 +316,7 @@ namespace {
 		if (bdecode_node const peers_entry = rd.dict_find_string("banned_peers"))
 		{
 			char const* ptr = peers_entry.string_ptr();
-			for (int i = 5; i < peers_entry.string_length(); i += 6)
+			for (int i = v4_size; i < peers_entry.string_length(); i += v4_size)
 				ret.banned_peers.push_back(read_v4_endpoint<tcp::endpoint>(ptr));
 		}
 
@@ -320,7 +324,7 @@ namespace {
 		if (bdecode_node const peers_entry = rd.dict_find_string("banned_peers6"))
 		{
 			char const* ptr = peers_entry.string_ptr();
-			for (int i = 17; i < peers_entry.string_length(); i += 18)
+			for (int i = v6_size - 1; i < peers_entry.string_length(); i += v6_size)
 				ret.banned_peers.push_back(read_v6_endpoint<tcp::endpoint>(ptr));
 		}
 #endif
@@ -338,7 +342,7 @@ namespace {
 				bdecode_node const bitmask = e.dict_find_string("bitmask");
 				if (!bitmask || bitmask.string_length() == 0) continue;
 				ret.unfinished_pieces[piece].assign(
-					bitmask.string_ptr(), bitmask.string_length() * 8);
+					bitmask.string_ptr(), bitmask.string_length() * CHAR_BIT);
 			}
 		}