Compact serialization for amounts

Special serializer/deserializer for amount values. It is optimized for
values which have few non-zero digits in decimal representation. Most
amounts currently in the txout set take only 1 or 2 bytes to
represent.

src/test/compress_tests.cpp

@@ -0,0 +1,62 @@
+#include <boost/test/unit_test.hpp>
+
+#include <string>
+#include <vector>
+
+#include "main.h"
+
+// amounts 0.00000001 .. 0.00100000
+#define NUM_MULTIPLES_UNIT 100000
+
+// amounts 0.01 .. 100.00
+#define NUM_MULTIPLES_CENT 10000
+
+// amounts 1 .. 10000
+#define NUM_MULTIPLES_1BTC 10000
+
+// amounts 50 .. 21000000
+#define NUM_MULTIPLES_50BTC 420000
+
+using namespace std;
+
+BOOST_AUTO_TEST_SUITE(compress_tests)
+
+bool static TestEncode(uint64 in) {
+    return in == CTxOutCompressor::DecompressAmount(CTxOutCompressor::CompressAmount(in));
+}
+
+bool static TestDecode(uint64 in) {
+    return in == CTxOutCompressor::CompressAmount(CTxOutCompressor::DecompressAmount(in));
+}
+
+bool static TestPair(uint64 dec, uint64 enc) {
+    return CTxOutCompressor::CompressAmount(dec) == enc &&
+           CTxOutCompressor::DecompressAmount(enc) == dec;
+}
+
+BOOST_AUTO_TEST_CASE(compress_amounts)
+{
+    BOOST_CHECK(TestPair(            0,       0x0));
+    BOOST_CHECK(TestPair(            1,       0x1));
+    BOOST_CHECK(TestPair(         CENT,       0x7));
+    BOOST_CHECK(TestPair(         COIN,       0x9));
+    BOOST_CHECK(TestPair(      50*COIN,      0x32));
+    BOOST_CHECK(TestPair(21000000*COIN, 0x1406f40));
+
+    for (uint64 i = 1; i <= NUM_MULTIPLES_UNIT; i++)
+        BOOST_CHECK(TestEncode(i));
+
+    for (uint64 i = 1; i <= NUM_MULTIPLES_CENT; i++)
+        BOOST_CHECK(TestEncode(i * CENT));
+
+    for (uint64 i = 1; i <= NUM_MULTIPLES_1BTC; i++)
+        BOOST_CHECK(TestEncode(i * COIN));
+
+    for (uint64 i = 1; i <= NUM_MULTIPLES_50BTC; i++)
+        BOOST_CHECK(TestEncode(i * 50 * COIN));
+
+    for (uint64 i = 0; i < 100000; i++)
+        BOOST_CHECK(TestDecode(i));
+}
+
+BOOST_AUTO_TEST_SUITE_END()