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# Creates a decentralized market between any two subcurrencies
# Here, the first subcurrency is the base asset and the second
# subcurrency is the asset priced against the base asset. Hence,
# "buying" refers to trading the first for the second, and
# "selling" refers to trading the second for the first
# storage 0: buy orders
# storage 1: sell orders
# storage 1000: first subcurrency
# storage 1001: last first subcurrency txid
# storage 2000: second subcurrency
# storage 2001: last second subcurrency txid
# storage 3000: current epoch
# storage 4000: price
# storage 4001: volume
init:
# Heap for buy orders
contract.storage[0] = create('heap.se')
# Heap for sell orders
contract.storage[1] = create('heap.se')
code:
# Initialize with [ first_subcurrency, second_subcurrency ]
if !contract.storage[1000]:
contract.storage[1000] = msg.data[0] # First subcurrency
contract.storage[1001] = -1
contract.storage[2000] = msg.data[1] # Second subcurrency
contract.storage[2001] = -1
contract.storage[3000] = block.number / 1000
stop
first_subcurrency = contract.storage[1000]
second_subcurrency = contract.storage[2000]
buy_heap = contract.storage[0]
sell_heap = contract.storage[1]
# This contract operates in "epochs" of 100 blocks
# At the end of each epoch, we process all orders
# simultaneously, independent of order. This algorithm
# prevents front-running, and generates a profit from
# the spread. The profit is permanently kept in the
# market (ie. destroyed), making both subcurrencies
# more valuable
# Epoch transition code
if contract.storage[3000] < block.number / 100:
done = 0
volume = 0
while !done:
# Grab the top buy and sell order from each heap
topbuy = call(buy_heap, 1)
topsell = call(sell_heap, 1)
# An order is recorded in the heap as:
# Buys: (2^48 - 1 - price) * 2^208 + units of first currency * 2^160 + from
# Sells: price * 2^208 + units of second currency * 2^160 + from
buyprice = -(topbuy / 2^208)
buyfcvalue = (topbuy / 2^160) % 2^48
buyer = topbuy % 2^160
sellprice = topsell / 2^208
sellscvalue = (topsell / 2^160) % 2^48
seller = topsell % 2^160
# Heap empty, or no more matching orders
if not topbuy or not topsell or buyprice < sellprice:
done = 1
else:
# Add to volume counter
volume += buyfcvalue
# Calculate how much of the second currency the buyer gets, and
# how much of the first currency the seller gets
sellfcvalue = sellscvalue / buyprice
buyscvalue = buyfcvalue * sellprice
# Send the currency units along
call(second_subcurrency, [buyer, buyscvalue], 2)
call(first_subcurrency, [seller, sellfcvalue], 2)
if volume:
contract.storage[4000] = (buyprice + sellprice) / 2
contract.storage[4001] = volume
contract.storage[3000] = block.number / 100
# Make buy order [0, price]
if msg.data[0] == 0:
# We ask the first subcurrency contract what the last transaction was. The
# way to make a buy order is to send the amount of first currency units that
# you wish to buy with, and then immediately call this contract. For security
# it makes sense to set up a tx which sends both messages in sequence atomically
data = call(first_subcurrency, [], 0, 4)
from = data[0]
to = data[1]
value = data[2]
txid = data[3]
price = msg.data[1]
if txid > contract.storage[1001] and to == contract.address:
contract.storage[1001] = txid
# Adds the order to the heap
call(buy_heap, [0, -price * 2^208 + (value % 2^48) * 2^160 + from], 2)
# Make sell order [1, price]
elif msg.data[0] == 1:
# Same mechanics as buying
data = call(second_subcurrency, [], 0, 4)
from = data[0]
to = data[1]
value = data[2]
txid = data[3]
price = msg.data[1]
if txid > contract.storage[2001] and to == contract.address:
contract.storage[2001] = txid
call(sell_heap, [0, price * 2^208 + (value % 2^48) * 2^160 + from], 2)
# Ask for price
elif msg.data[0] == 2:
return(contract.storage[4000])
# Ask for volume
elif msg.data[0] == 3:
return(contract.storage[1000])
# Ask for first currency
elif msg.data[0] == 4:
return(contract.storage[2000])
# Ask for second currency
elif msg.data[0] == 5:
return(contract.storage[4001])
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