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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.
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sipa committed Jun 16, 2012
1 parent 69fc804 commit 0fa593d0fb3a6f731a31610e98ce6bfd6a50a96c
Showing with 130 additions and 3 deletions.
  1. +54 −0 src/main.cpp
  2. +14 −3 src/main.h
  3. +62 −0 src/test/compress_tests.cpp
@@ -4058,3 +4058,57 @@ void GenerateBitcoins(bool fGenerate, CWallet* pwallet)
}
}
}
// Amount compression:
// * If the amount is 0, output 0
// * first, divide the amount (in base units) by the largest power of 10 possible; call the exponent e (e is max 9)
// * if e<9, the last digit of the resulting number cannot be 0; store it as d, and drop it (divide by 10)
// * call the result n
// * output 1 + 10*(9*n + d - 1) + e
// * if e==9, we only know the resulting number is not zero, so output 1 + 10*(n - 1) + 9
// (this is decodable, as d is in [1-9] and e is in [0-9])
uint64 CTxOutCompressor::CompressAmount(uint64 n)
{
if (n == 0)
return 0;
int e = 0;
while (((n % 10) == 0) && e < 9) {
n /= 10;
e++;
}
if (e < 9) {
int d = (n % 10);
assert(d >= 1 && d <= 9);
n /= 10;
return 1 + (n*9 + d - 1)*10 + e;
} else {
return 1 + (n - 1)*10 + 9;
}
}
uint64 CTxOutCompressor::DecompressAmount(uint64 x)
{
// x = 0 OR x = 1+10*(9*n + d - 1) + e OR x = 1+10*(n - 1) + 9
if (x == 0)
return 0;
x--;
// x = 10*(9*n + d - 1) + e
int e = x % 10;
x /= 10;
uint64 n = 0;
if (e < 9) {
// x = 9*n + d - 1
int d = (x % 9) + 1;
x /= 9;
// x = n
n = x*10 + d;
} else {
n = x+1;
}
while (e) {
n *= 10;
e--;
}
return n;
}
@@ -652,14 +652,25 @@ class CTxOutCompressor
{
private:
CTxOut &txout;
public:
static uint64 CompressAmount(uint64 nAmount);
static uint64 DecompressAmount(uint64 nAmount);
CTxOutCompressor(CTxOut &txoutIn) : txout(txoutIn) { }
IMPLEMENT_SERIALIZE(
READWRITE(VARINT(txout.nValue));
IMPLEMENT_SERIALIZE(({
if (!fRead) {
uint64 nVal = CompressAmount(txout.nValue);
READWRITE(VARINT(nVal));
} else {
uint64 nVal = 0;
READWRITE(VARINT(nVal));
txout.nValue = DecompressAmount(nVal);
}
CScriptCompressor cscript(REF(txout.scriptPubKey));
READWRITE(cscript);
)
});)
};
@@ -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()

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