From a93429c5dbedbe3fb34d9ed16cef0dc5956bceb6 Mon Sep 17 00:00:00 2001
From: arvidn <arvid@libtorrent.org>
Date: Tue, 9 Jan 2018 01:34:04 +0100
Subject: [PATCH] modernize piece-size selection in torrent creator and add a
 test

---
 src/create_torrent.cpp       | 20 +++++++++++++++-----
 test/test_create_torrent.cpp | 28 ++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 5 deletions(-)

diff --git a/src/create_torrent.cpp b/src/create_torrent.cpp
index 71f69e7fb..ba705ffcb 100644
--- a/src/create_torrent.cpp
+++ b/src/create_torrent.cpp
@@ -333,15 +333,25 @@ namespace {
 			//   target_piece_size = total_size / (target_list_size / hash_size);
 			// Given hash_size = 20 bytes, target_piece_size = (16*1024 * pow(2, i))
 			// we can determine size_table = (total_size = pow(2 * target_piece_size / hash_size, 2))
-			std::int64_t const size_table[] = {2684355, 10737418, 42949673, 171798692, 687194767,
-				2748779069LL, 10995116278LL, 43980465111LL, 175921860444LL, 703687441777LL};
+			std::array<std::int64_t, 10> const size_table{{
+				       2684355LL // ->  16kiB
+				,     10737418LL // ->  32 kiB
+				,     42949673LL // ->  64 kiB
+				,    171798692LL // -> 128 kiB
+				,    687194767LL // -> 256 kiB
+				,   2748779069LL // -> 512 kiB
+				,  10995116278LL // -> 1 MiB
+				,  43980465111LL // -> 2 MiB
+				, 175921860444LL // -> 4 MiB
+				, 703687441777LL}}; // -> 8 MiB
 
 			int i = 0;
-			for (int max = sizeof(size_table) / sizeof(size_table[0]); i < max; ++i)
+			for (auto const s : size_table)
 			{
-				if (size_table[i] >= fs.total_size()) break;
+				if (s >= fs.total_size()) break;
+				++i;
 			}
-			piece_size = 0x4000 << i;
+			piece_size = default_block_size << i;
 		}
 		else if (piece_size == 0 && m_merkle_torrent)
 		{
diff --git a/test/test_create_torrent.cpp b/test/test_create_torrent.cpp
index 534c52097..d13464a76 100644
--- a/test/test_create_torrent.cpp
+++ b/test/test_create_torrent.cpp
@@ -70,3 +70,31 @@ TORRENT_TEST(create_verbatim_torrent)
 	TEST_CHECK(memcmp(dest_info, test_torrent + 1, sizeof(test_torrent)-3) == 0);
 }
 
+TORRENT_TEST(piece_size)
+{
+	std::int64_t const kiB = 1024;
+	std::int64_t const MiB = 1024 * 1024;
+	std::int64_t const GiB = 1024 * 1024 * 1024;
+	std::array<std::pair<std::int64_t, std::int64_t>, 11> samples{{
+		{100LL,     16 * kiB},
+		{3 * MiB,   32 * kiB},
+		{11 * MiB,  64 * kiB},
+		{43 * MiB,  128 * kiB},
+		{172 * MiB, 256 * kiB},
+		{688 * MiB, 512 * kiB},
+		{3 * GiB,   1 * MiB},
+		{11 * GiB,  2 * MiB},
+		{44 * GiB,  4 * MiB},
+		{176 * GiB, 8 * MiB},
+		{704 * GiB, 16 * MiB},
+	}};
+
+	for (auto const& t : samples)
+	{
+		lt::file_storage fs;
+		fs.add_file("a", t.first);
+		lt::create_torrent ct(fs, 0);
+		TEST_CHECK(ct.piece_length() == static_cast<int>(t.second));
+	}
+}
+