/
ar_pricing.erl
834 lines (777 loc) · 32.4 KB
/
ar_pricing.erl
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-module(ar_pricing).
%% 2.6 exports.
-export([is_v2_pricing_height/1, get_price_per_gib_minute/4, get_tx_fee/1,
get_miner_reward_endowment_pool_debt_supply/1, recalculate_price_per_gib_minute/1,
redenominate/3, may_be_redenominate/1]).
%% 2.5 exports.
-export([get_tx_fee/4, get_miner_reward_and_endowment_pool/1, get_tx_fee_pre_fork_2_4/4,
usd_to_ar_rate/1, usd_to_ar/3, recalculate_usd_to_ar_rate/1, usd_to_ar_pre_fork_2_4/3,
get_miner_reward_and_endowment_pool_pre_fork_2_4/1, get_storage_cost/4,
get_expected_min_decline_rate/6]).
-include_lib("arweave/include/ar.hrl").
-include_lib("arweave/include/ar_inflation.hrl").
-include_lib("arweave/include/ar_pricing.hrl").
-include_lib("arweave/include/ar_consensus.hrl").
-include_lib("eunit/include/eunit.hrl").
%%%===================================================================
%%% Types.
%%%===================================================================
-type nonegint() :: non_neg_integer().
-type fraction() :: {integer(), integer()}.
-type usd() :: float() | fraction().
-type date() :: {nonegint(), nonegint(), nonegint()}.
-type time() :: {nonegint(), nonegint(), nonegint()}.
-type datetime() :: {date(), time()}.
%%%===================================================================
%%% Public interface 2.6.
%%%===================================================================
%% @doc Return true if the given height is a height where the transition to the
%% new pricing algorithm is complete.
is_v2_pricing_height(Height) ->
Fork_2_6_8 = ar_fork:height_2_6_8(),
Height >= Fork_2_6_8 % First check just this because it may be infinity.
andalso Height >= Fork_2_6_8 + (?PRICE_2_6_8_TRANSITION_START)
+ (?PRICE_2_6_8_TRANSITION_BLOCKS).
%% @doc Return the price per gibibyte minute estimated from the given history of
%% network hash rates and block rewards. The total reward used in calculations
%% is at least 1 Winston, even if all block rewards from the given history are 0.
%% Also, the returned price is always at least 1 Winston.
get_price_per_gib_minute(Height, RewardHistory, BlockTimeHistory, Denomination2) ->
Fork_2_7 = ar_fork:height_2_7(),
PriceTransitionStart = ar_fork:height_2_6_8() + ?PRICE_2_6_8_TRANSITION_START,
PriceTransitionEnd = PriceTransitionStart + ?PRICE_2_6_8_TRANSITION_BLOCKS,
PreTransitionPrice = ?PRICE_PER_GIB_MINUTE_PRE_TRANSITION,
NewPrice = get_price_per_gib_minute2(Height, RewardHistory, BlockTimeHistory, Denomination2),
case Height of
_ when Height < Fork_2_7 ->
%% Computed but not used at this point.
NewPrice;
_ when Height < PriceTransitionStart ->
PreTransitionPrice;
_ when Height < PriceTransitionEnd ->
%% Interpolate between the pre-transition price and the new price.
Interval1 = Height - PriceTransitionStart,
Interval2 = PriceTransitionEnd - Height,
PricePerGiBPerMinute =
(PreTransitionPrice * Interval2 + NewPrice * Interval1) div (Interval1 + Interval2),
?LOG_DEBUG([{event, get_price_per_gib_minute},
{height, Height}, {price1, PreTransitionPrice}, {price2, NewPrice},
{interval1, Interval1}, {interval2, Interval2},
{price, PricePerGiBPerMinute}]),
PricePerGiBPerMinute;
_ ->
NewPrice
end.
get_price_per_gib_minute2(Height, RewardHistory, BlockTimeHistory, Denomination2) ->
{HashRateTotal, RewardTotal} =
lists:foldl(
fun({_Addr, HashRate, Reward, Denomination}, {Acc1, Acc2}) ->
Reward2 = redenominate(Reward, Denomination, Denomination2),
{Acc1 + HashRate, Acc2 + Reward2}
end,
{0, 0},
RewardHistory
),
case Height - ?BLOCK_TIME_HISTORY_BLOCKS >= ar_fork:height_2_7() of
true ->
{IntervalTotal, VDFIntervalTotal, OneChunkCount, TwoChunkCount} =
lists:foldl(
fun({BlockInterval, VDFInterval, ChunkCount}, {Acc1, Acc2, Acc3, Acc4}) ->
{
Acc1 + BlockInterval,
Acc2 + VDFInterval,
case ChunkCount of
1 -> Acc3 + 1;
_ -> Acc3
end,
case ChunkCount of
1 -> Acc4;
_ -> Acc4 + 1
end
}
end,
{0, 0, 0, 0},
BlockTimeHistory
),
%% The intent of the SolutionsPerPartitionPerVDFStep is to estimate network replica
%% count (how many copies of the weave are stored across the network).
%% The logic behind this is complex - an explanation from @vird:
%%
%% 1. Naive solution: If we assume that each miner stores 1 replica, then we
%% can trivially calculate the network replica count using the network hashrate
%% (which we have) and the weave size (which we also have). However what if on
%% average each miner only stores 50% of the weave? In that case each miner will
%% get fewer hashes per partition (because they will miss out on 2-chunk solutions
%% that fall on the partitions they don't store), and that will push *up* the
%% replica count for a given network hashrate. How much to scale up our replica
%% count is based on the average replica count per miner.
%% 2. Estimate average replica count per miner: Start with this basic assumption:
%% the higher the percentage of the weave a miner stores, the more likely they are
%% to mine a 2-chunk solution. If a miner has 100% of the weave, then, on average,
%% 50% of their solutions will be 1-chunk, and 50% will be 2-chunk.
%%
%% With this we can use the ratio of observed 2-chunk to 1-chunk solutions to
%% estimate the average percentage of the weave each miner stores.
%%
%% The SolutionsPerPartitionPerVDFStep combines that average weave % calculation
%% with the expected number of solutions per partition per VDF step to arrive a single
%% number that can be used in the PricePerGiBPerMinute calculation.
SolutionsPerPartitionPerVDFStep =
case OneChunkCount of
0 ->
2 * (?RECALL_RANGE_SIZE) div (?DATA_CHUNK_SIZE);
_ ->
min(2 * ?RECALL_RANGE_SIZE,
?RECALL_RANGE_SIZE
+ ?RECALL_RANGE_SIZE * TwoChunkCount div OneChunkCount)
div ?DATA_CHUNK_SIZE
end,
%% The following walks through the math of calculating the price per GiB per minute.
%% However to reduce rounding errors due to divs, the uncommented equation at the
%% end is used instead. Logically they should be the same. Notably the '* 2' in
%% SolutionsPerPartitionPerBlock and the 'div 2' in PricePerGiBPerMinute cancel each
%% other out.
%%
%% SolutionsPerPartitionPerSecond =
%% (SolutionsPerPartitionPerVDFStep * VDFIntervalTotal) div IntervalTotal
%% SolutionsPerPartitionPerMinute = SolutionsPerPartitionPerSecond * 60,
%% SolutionsPerPartitionPerBlock = SolutionsPerPartitionPerMinute * 2,
%% EstimatedPartitionCount = max(1, HashRateTotal) div SolutionsPerPartitionPerBlock,
%% EstimatedDataSizeInGiB = EstimatedPartitionCount * (?PARTITION_SIZE) div (?GiB),
%% PricePerGiBPerBlock = max(1, RewardTotal) div EstimatedDataSizeInGiB,
%% PricePerGiBPerMinute = PricePerGibPerBlock div 2,
PricePerGiBPerMinute =
(
(SolutionsPerPartitionPerVDFStep * VDFIntervalTotal) *
max(1, RewardTotal) * (?GiB) * 60
)
div
(
IntervalTotal * max(1, HashRateTotal) * (?PARTITION_SIZE)
),
?LOG_DEBUG([{event, get_price_per_gib_minute2}, {height, Height},
{hash_rate_total, HashRateTotal}, {reward_total, RewardTotal},
{interval_total, IntervalTotal}, {vdf_interval_total, VDFIntervalTotal},
{one_chunk_count, OneChunkCount}, {two_chunk_count, TwoChunkCount},
{solutions_per_partition_per_vdf_step, SolutionsPerPartitionPerVDFStep},
{price, PricePerGiBPerMinute}]),
PricePerGiBPerMinute;
false ->
%% 2 recall ranges per partition per second.
SolutionsPerPartitionPerSecond = 2 * (?RECALL_RANGE_SIZE) div (?DATA_CHUNK_SIZE),
SolutionsPerPartitionPerMinute = SolutionsPerPartitionPerSecond * 60,
SolutionsPerPartitionPerBlock = SolutionsPerPartitionPerMinute * 2,
%% Estimated partition count = hash rate / 2 / solutions per partition per minute.
%% 2 minutes is the average block time.
%% Estimated data size = estimated partition count * partition size.
%% Estimated price per gib minute = total block reward / estimated data size
%% in gibibytes.
(max(1, RewardTotal) * (?GiB) * SolutionsPerPartitionPerBlock)
div (max(1, HashRateTotal)
* (?PARTITION_SIZE)
* 2 % The reward is paid every two minutes whereas we are calculating
% the minute rate here.
)
end.
%% @doc Return the minimum required transaction fee for the given number of
%% total bytes stored and gibibyte minute price.
get_tx_fee(Args) ->
{DataSize, GiBMinutePrice, KryderPlusRateMultiplier, Height} = Args,
FirstYearPrice = DataSize * GiBMinutePrice * 60 * 24 * 365,
{LnDecayDividend, LnDecayDivisor} = ?LN_PRICE_DECAY_ANNUAL,
PerpetualPrice = {-FirstYearPrice * LnDecayDivisor * KryderPlusRateMultiplier
* (?N_REPLICATIONS(Height)), LnDecayDividend * (?GiB)},
MinerShare = ar_fraction:multiply(PerpetualPrice,
?MINER_MINIMUM_ENDOWMENT_CONTRIBUTION_SHARE),
{Dividend, Divisor} = ar_fraction:add(PerpetualPrice, MinerShare),
Dividend div Divisor.
%% @doc Return the block reward, the new endowment pool, and the new debt supply.
get_miner_reward_endowment_pool_debt_supply(Args) ->
{EndowmentPool, DebtSupply, TXs, WeaveSize, Height, GiBMinutePrice,
KryderPlusRateMultiplierLatch, KryderPlusRateMultiplier, Denomination,
BlockInterval} = Args,
Inflation = redenominate(ar_inflation:calculate(Height), 1, Denomination),
ExpectedReward = (?N_REPLICATIONS(Height)) * WeaveSize * GiBMinutePrice
* BlockInterval div (60 * ?GiB),
{EndowmentPoolFeeShare, MinerFeeShare} = distribute_transaction_fees2(TXs, Denomination),
BaseReward = Inflation + MinerFeeShare,
EndowmentPool2 = EndowmentPool + EndowmentPoolFeeShare,
case BaseReward >= ExpectedReward of
true ->
{BaseReward, EndowmentPool2, DebtSupply, KryderPlusRateMultiplierLatch,
KryderPlusRateMultiplier};
false ->
Take = ExpectedReward - BaseReward,
{EndowmentPool3, DebtSupply2} =
case Take > EndowmentPool2 of
true ->
{0, DebtSupply + Take - EndowmentPool2};
false ->
{EndowmentPool2 - Take, DebtSupply}
end,
{KryderPlusRateMultiplierLatch2, KryderPlusRateMultiplier2} =
case {Take > EndowmentPool2, KryderPlusRateMultiplierLatch} of
{true, 0} ->
{1, KryderPlusRateMultiplier * 2};
{false, 1} ->
Threshold = redenominate(?RESET_KRYDER_PLUS_LATCH_THRESHOLD, 1,
Denomination),
case EndowmentPool3 > Threshold of
true ->
{0, KryderPlusRateMultiplier};
false ->
{1, KryderPlusRateMultiplier}
end;
_ ->
{KryderPlusRateMultiplierLatch, KryderPlusRateMultiplier}
end,
{BaseReward + Take, EndowmentPool3, DebtSupply2, KryderPlusRateMultiplierLatch2,
KryderPlusRateMultiplier2}
end.
%% @doc Return the new current and scheduled prices per byte minute.
recalculate_price_per_gib_minute(B) ->
#block{ height = PrevHeight } = B,
Height = PrevHeight + 1,
Fork_2_6 = ar_fork:height_2_6(),
true = Height >= Fork_2_6,
case Height > Fork_2_6 of
false ->
get_initial_current_and_scheduled_price_per_gib_minute(B);
true ->
recalculate_price_per_gib_minute2(B)
end.
%% @doc Return the denominated amount.
redenominate(Amount, 0, _Denomination) ->
Amount;
redenominate(Amount, BaseDenomination, BaseDenomination) ->
Amount;
redenominate(Amount, BaseDenomination, Denomination) when Denomination > BaseDenomination ->
redenominate(Amount * 1000, BaseDenomination, Denomination - 1).
%% @doc Increase the amount of base currency units in the system if
%% the available supply is too low.
may_be_redenominate(B) ->
#block{ height = Height, denomination = Denomination,
redenomination_height = RedenominationHeight } = B,
case is_v2_pricing_height(Height + 1) of
false ->
{Denomination, RedenominationHeight};
true ->
may_be_redenominate2(B)
end.
may_be_redenominate2(B) ->
#block{ height = Height, denomination = Denomination,
redenomination_height = RedenominationHeight } = B,
case Height == RedenominationHeight of
true ->
{Denomination + 1, RedenominationHeight};
false ->
case Height < RedenominationHeight of
true ->
{Denomination, RedenominationHeight};
false ->
may_be_redenominate3(B)
end
end.
may_be_redenominate3(B) ->
#block{ height = Height, debt_supply = DebtSupply, reward_pool = EndowmentPool,
denomination = Denomination, redenomination_height = RedenominationHeight } = B,
TotalSupply = get_total_supply(Denomination),
case TotalSupply + DebtSupply - EndowmentPool < (?REDENOMINATION_THRESHOLD) of
true ->
{Denomination, Height + (?REDENOMINATION_DELAY_BLOCKS)};
false ->
{Denomination, RedenominationHeight}
end.
get_initial_current_and_scheduled_price_per_gib_minute(B) ->
#block{ diff = Diff, height = Height } = B,
HashRate = ar_difficulty:get_hash_rate(Diff),
Reward = ar_inflation:calculate(B#block.height),
Denomination = 1,
Price = get_price_per_gib_minute(Height,
[{B#block.reward_addr, HashRate, Reward, Denomination}],
B#block.block_time_history, Denomination),
{Price, Price}.
recalculate_price_per_gib_minute2(B) ->
#block{ height = PrevHeight, reward_history = RewardHistory,
block_time_history = BlockTimeHistory,
denomination = Denomination, price_per_gib_minute = Price,
scheduled_price_per_gib_minute = ScheduledPrice } = B,
Height = PrevHeight + 1,
Fork_2_7 = ar_fork:height_2_7(),
Fork_2_7_1 = ar_fork:height_2_7_1(),
case Height of
Fork_2_7 ->
{?PRICE_PER_GIB_MINUTE_PRE_TRANSITION,
?PRICE_PER_GIB_MINUTE_PRE_TRANSITION};
Height when Height < Fork_2_7_1 ->
case is_price_adjustment_height(Height) of
false ->
{Price, ScheduledPrice};
true ->
%% price_per_gib_minute = scheduled_price_per_gib_minute
%% scheduled_price_per_gib_minute = get_price_per_gib_minute() capped to
%% 0.5x to 2x of old price_per_gib_minute
RewardHistory2 = lists:sublist(RewardHistory, ?REWARD_HISTORY_BLOCKS),
BlockTimeHistory2 = lists:sublist(BlockTimeHistory,
?BLOCK_TIME_HISTORY_BLOCKS),
Price2 = min(Price * 2, get_price_per_gib_minute(Height,
RewardHistory2, BlockTimeHistory2, Denomination)),
Price3 = max(Price div 2, Price2),
{ScheduledPrice, Price3}
end;
_ ->
case is_price_adjustment_height(Height) of
false ->
{Price, ScheduledPrice};
true ->
%% price_per_gib_minute = scheduled_price_per_gib_minute
%% scheduled_price_per_gib_minute =
%% get_price_per_gib_minute()
%% EMA'ed with scheduled_price_per_gib_minute at 0.1 alpha
%% and then capped to 0.5x to 2x of scheduled_price_per_gib_minute
RewardHistory2 = lists:sublist(RewardHistory, ?REWARD_HISTORY_BLOCKS),
BlockTimeHistory2 = lists:sublist(BlockTimeHistory,
?BLOCK_TIME_HISTORY_BLOCKS),
TargetPrice = get_price_per_gib_minute(Height,
RewardHistory2, BlockTimeHistory2, Denomination),
EMAPrice = (9 * ScheduledPrice + TargetPrice) div 10,
Price2 = min(ScheduledPrice * 2, EMAPrice),
Price3 = max(ScheduledPrice div 2, Price2),
?LOG_DEBUG([{event, recalculate_price_per_gib_minute},
{height, Height},
{old_price, Price},
{scheduled_price, ScheduledPrice},
{target_price, TargetPrice},
{ema_price, EMAPrice},
{capped_price, Price3}]),
{ScheduledPrice, Price3}
end
end.
is_price_adjustment_height(Height) ->
Height rem ?PRICE_ADJUSTMENT_FREQUENCY == 0.
distribute_transaction_fees2(TXs, Denomination) ->
distribute_transaction_fees2(TXs, 0, 0, Denomination).
distribute_transaction_fees2([], EndowmentPoolTotal, MinerTotal, _Denomination) ->
{EndowmentPoolTotal, MinerTotal};
distribute_transaction_fees2([TX | TXs], EndowmentPoolTotal, MinerTotal, Denomination) ->
TXFee = redenominate(TX#tx.reward, TX#tx.denomination, Denomination),
{Dividend, Divisor} = ?MINER_FEE_SHARE,
MinerFee = TXFee * Dividend div Divisor,
EndowmentPoolTotal2 = EndowmentPoolTotal + TXFee - MinerFee,
MinerTotal2 = MinerTotal + MinerFee,
distribute_transaction_fees2(TXs, EndowmentPoolTotal2, MinerTotal2, Denomination).
get_total_supply(Denomination) ->
redenominate(?TOTAL_SUPPLY, 1, Denomination).
%%%===================================================================
%%% Public interface 2.5.
%%%===================================================================
%% @doc Return the perpetual cost of storing the given amount of data.
get_storage_cost(DataSize, Timestamp, Rate, Height) ->
Size = ?TX_SIZE_BASE + DataSize,
PerpetualGBStorageCost =
usd_to_ar(
get_perpetual_gb_cost_at_timestamp(Timestamp, Height),
Rate,
Height
),
StorageCost = max(1, PerpetualGBStorageCost div (1024 * 1024 * 1024)) * Size,
HashingCost = StorageCost,
StorageCost + HashingCost.
%% @doc Calculate the transaction fee.
get_tx_fee(DataSize, Timestamp, Rate, Height) ->
MaintenanceCost = get_storage_cost(DataSize, Timestamp, Rate, Height),
MinerFeeShare = get_miner_fee_share(MaintenanceCost, Height),
MaintenanceCost + MinerFeeShare.
%% @doc Return the miner reward and the new endowment pool.
get_miner_reward_and_endowment_pool({Pool, TXs, unclaimed, _, _, _, _}) ->
{0, Pool + lists:sum([TX#tx.reward || TX <- TXs])};
get_miner_reward_and_endowment_pool(Args) ->
{Pool, TXs, _Addr, WeaveSize, Height, Timestamp, Rate} = Args,
Inflation = trunc(ar_inflation:calculate(Height)),
{PoolFeeShare, MinerFeeShare} = distribute_transaction_fees(TXs, Height),
BaseReward = Inflation + MinerFeeShare,
StorageCostPerGBPerBlock =
usd_to_ar(
get_gb_cost_per_block_at_timestamp(Timestamp, Height),
Rate,
Height
),
Burden = WeaveSize * StorageCostPerGBPerBlock div (1024 * 1024 * 1024),
Pool2 = Pool + PoolFeeShare,
case BaseReward >= Burden of
true ->
{BaseReward, Pool2};
false ->
Take = min(Pool2, Burden - BaseReward),
{BaseReward + Take, Pool2 - Take}
end.
%% @doc Calculate the transaction fee.
get_tx_fee_pre_fork_2_4(Size, Diff, Height, Timestamp) ->
GBs = (?TX_SIZE_BASE + Size) / (1024 * 1024 * 1024),
true = Height >= ar_fork:height_2_0(),
PerGB =
usd_to_ar_pre_fork_2_4(
get_perpetual_gb_cost_at_timestamp(Timestamp, Height),
Diff,
Height
),
StorageCost = PerGB * GBs,
HashingCost = StorageCost,
MaintenanceCost = erlang:trunc(StorageCost + HashingCost),
MinerFeeShare = get_miner_fee_share(MaintenanceCost, Height),
MaintenanceCost + MinerFeeShare.
%% @doc Return the miner reward and the new endowment pool.
get_miner_reward_and_endowment_pool_pre_fork_2_4({Pool, TXs, unclaimed, _, _, _, _}) ->
{0, Pool + lists:sum([TX#tx.reward || TX <- TXs])};
get_miner_reward_and_endowment_pool_pre_fork_2_4(Args) ->
{Pool, TXs, _RewardAddr, WeaveSize, Height, Diff, Timestamp} = Args,
true = Height >= ar_fork:height_2_0(),
Inflation = trunc(ar_inflation:calculate(Height)),
{PoolFeeShare, MinerFeeShare} = distribute_transaction_fees(TXs, Height),
BaseReward = Inflation + MinerFeeShare,
StorageCostPerGBPerBlock =
usd_to_ar_pre_fork_2_4(
get_gb_cost_per_block_at_timestamp(Timestamp, Height),
Diff,
Height
),
Burden = trunc(WeaveSize * StorageCostPerGBPerBlock / (1024 * 1024 * 1024)),
Pool2 = Pool + PoolFeeShare,
case BaseReward >= Burden of
true ->
{BaseReward, Pool2};
false ->
Take = min(Pool2, Burden - BaseReward),
{BaseReward + Take, Pool2 - Take}
end.
%% @doc Return the effective USD to AR rate corresponding to the given block
%% considering its previous block.
usd_to_ar_rate(#block{ height = PrevHeight } = PrevB) ->
Height_2_5 = ar_fork:height_2_5(),
Height = PrevHeight + 1,
case PrevHeight < Height_2_5 of
true ->
?INITIAL_USD_TO_AR(Height)();
false ->
PrevB#block.usd_to_ar_rate
end.
%% @doc Return the amount of AR the given number of USD is worth.
usd_to_ar(USD, Rate, Height) when is_number(USD) ->
usd_to_ar({USD, 1}, Rate, Height);
usd_to_ar({Dividend, Divisor}, Rate, Height) ->
InitialInflation = trunc(ar_inflation:calculate(?INITIAL_USD_TO_AR_HEIGHT(Height)())),
CurrentInflation = trunc(ar_inflation:calculate(Height)),
{InitialRateDividend, InitialRateDivisor} = Rate,
trunc( Dividend
* ?WINSTON_PER_AR
* CurrentInflation
* InitialRateDividend )
div Divisor
div InitialInflation
div InitialRateDivisor.
recalculate_usd_to_ar_rate(#block{ height = PrevHeight } = B) ->
Height = PrevHeight + 1,
Fork_2_5 = ar_fork:height_2_5(),
true = Height >= Fork_2_5,
case Height > Fork_2_5 of
false ->
Rate = ?INITIAL_USD_TO_AR(Height)(),
{Rate, Rate};
true ->
Fork_2_6 = ar_fork:height_2_6(),
case Height == Fork_2_6 of
true ->
{B#block.usd_to_ar_rate, ?FORK_2_6_PRE_TRANSITION_USD_TO_AR_RATE};
false ->
recalculate_usd_to_ar_rate2(B)
end
end.
%% @doc Return the amount of AR the given number of USD is worth.
usd_to_ar_pre_fork_2_4(USD, Diff, Height) ->
InitialDiff =
ar_retarget:switch_to_linear_diff_pre_fork_2_4(?INITIAL_USD_TO_AR_DIFF(Height)()),
MaxDiff = ?MAX_DIFF,
DeltaP = (MaxDiff - InitialDiff) / (MaxDiff - Diff),
InitialInflation = ar_inflation:calculate(?INITIAL_USD_TO_AR_HEIGHT(Height)()),
DeltaInflation = ar_inflation:calculate(Height) / InitialInflation,
erlang:trunc(
(USD * ?WINSTON_PER_AR * DeltaInflation) / (?INITIAL_USD_PER_AR(Height)() * DeltaP)
).
%% @doc Return an estimation for the minimum required decline rate making the given
%% Amount (in Winston) sufficient to subsidize storage for Period seconds starting from
%% Timestamp and assuming the given USD to AR rate.
%% When computing the exponent, the function accounts for the first 16 summands in
%% the Taylor series. The fraction is reduced to the 1/1000000 precision.
get_expected_min_decline_rate(Timestamp, Period, Amount, Size, Rate, Height) ->
{USDDiv1, USDDivisor1} = get_gb_cost_per_year_at_timestamp(Timestamp, Height),
%% Multiply by 2 to account for hashing costs.
Sum1 = 2 * usd_to_ar({USDDiv1, USDDivisor1}, Rate, Height),
{USDDiv2, USDDivisor2} = get_gb_cost_per_year_at_timestamp(Timestamp + Period, Height),
Sum2 = 2 * usd_to_ar({USDDiv2, USDDivisor2}, Rate, Height),
%% Sum1 / -logRate - Sum2 / -logRate = Amount
%% => -logRate = (Sum1 - Sum2) / Amount
%% => 1 / Rate = exp((Sum1 - Sum2) / Amount)
%% => Rate = 1 / exp((Sum1 - Sum2) / Amount)
{ExpDiv, ExpDivisor} = ar_fraction:natural_exponent(
{(Sum1 - Sum2) * Size, Amount * (1024 * 1024 * 1024)}, 16),
ar_fraction:reduce({ExpDivisor, ExpDiv}, 1000000).
%%%===================================================================
%%% Private functions.
%%%===================================================================
%% @doc Get the share of the maintenance cost the miner receives for a transation.
get_miner_fee_share(MaintenanceCost, Height) ->
{Dividend, Divisor} = ?MINING_REWARD_MULTIPLIER,
case Height >= ar_fork:height_2_5() of
false ->
erlang:trunc(MaintenanceCost * (Dividend / Divisor));
true ->
MaintenanceCost * Dividend div Divisor
end.
distribute_transaction_fees(TXs, Height) ->
distribute_transaction_fees(TXs, 0, 0, Height).
distribute_transaction_fees([], EndowmentPool, Miner, _Height) ->
{EndowmentPool, Miner};
distribute_transaction_fees([TX | TXs], EndowmentPool, Miner, Height) ->
TXFee = TX#tx.reward,
{Dividend, Divisor} = ?MINING_REWARD_MULTIPLIER,
MinerFee =
case Height >= ar_fork:height_2_5() of
false ->
erlang:trunc((Dividend / Divisor) * TXFee / ((Dividend / Divisor) + 1));
true ->
TXFee * Dividend div (Dividend + Divisor)
end,
distribute_transaction_fees(TXs, EndowmentPool + TXFee - MinerFee, Miner + MinerFee,
Height).
%% @doc Return the cost of storing 1 GB in the network perpetually.
%% Integral of the exponential decay curve k*e^(-at), i.e. k/a.
%% @end
-spec get_perpetual_gb_cost_at_timestamp(Timestamp::integer(), Height::nonegint()) -> usd().
get_perpetual_gb_cost_at_timestamp(Timestamp, Height) ->
K = get_gb_cost_per_year_at_timestamp(Timestamp, Height),
get_perpetual_gb_cost(K, Height).
-spec get_perpetual_gb_cost(Init::usd(), Height::nonegint()) -> usd().
get_perpetual_gb_cost(Init, Height) ->
case Height >= ar_fork:height_2_5() of
true ->
{LnDecayDividend, LnDecayDivisor} = ?LN_PRICE_DECAY_ANNUAL,
{InitDividend, InitDivisor} = Init,
{-InitDividend * LnDecayDivisor, InitDivisor * LnDecayDividend};
false ->
{Dividend, Divisor} = ?PRICE_DECAY_ANNUAL,
Init / -math:log(Dividend / Divisor)
end.
%% @doc Return the cost in USD of storing 1 GB per year at the given time.
-spec get_gb_cost_per_year_at_timestamp(Timestamp::integer(), Height::nonegint()) -> usd().
get_gb_cost_per_year_at_timestamp(Timestamp, Height) ->
Datetime = system_time_to_universal_time(Timestamp, seconds),
get_gb_cost_per_year_at_datetime(Datetime, Height).
%% @doc Return the cost in USD of storing 1 GB per average block time at the given time.
-spec get_gb_cost_per_block_at_timestamp(integer(), nonegint()) -> usd().
get_gb_cost_per_block_at_timestamp(Timestamp, Height) ->
Datetime = system_time_to_universal_time(Timestamp, seconds),
get_gb_cost_per_block_at_datetime(Datetime, Height).
%% @doc Return the cost in USD of storing 1 GB per year.
-spec get_gb_cost_per_year_at_datetime(DT::datetime(), Height::nonegint()) -> usd().
get_gb_cost_per_year_at_datetime({{Y, M, _}, _} = DT, Height) ->
PrevY = prev_jun_30_year(Y, M),
NextY = next_jun_30_year(Y, M),
FracY = fraction_of_year(PrevY, NextY, DT, Height),
PrevYCost = usd_p_gby(PrevY, Height),
NextYCost = usd_p_gby(NextY, Height),
case Height >= ar_fork:height_2_5() of
true ->
{FracYDividend, FracYDivisor} = FracY,
{PrevYCostDividend, PrevYCostDivisor} = PrevYCost,
{NextYCostDividend, NextYCostDivisor} = NextYCost,
Dividend =
(?N_REPLICATIONS(Height))
* (
PrevYCostDividend * NextYCostDivisor * FracYDivisor
- FracYDividend
* (
PrevYCostDividend
* NextYCostDivisor
- NextYCostDividend
* PrevYCostDivisor
)
),
Divisor =
PrevYCostDivisor
* NextYCostDivisor
* FracYDivisor,
{Dividend, Divisor};
false ->
CY = PrevYCost - (FracY * (PrevYCost - NextYCost)),
CY * (?N_REPLICATIONS(Height))
end.
prev_jun_30_year(Y, M) when M < 7 ->
Y - 1;
prev_jun_30_year(Y, _M) ->
Y.
next_jun_30_year(Y, M) when M < 7 ->
Y;
next_jun_30_year(Y, _M) ->
Y + 1.
%% @doc Return the cost in USD of storing 1 GB per average block time.
-spec get_gb_cost_per_block_at_datetime(DT::datetime(), Height::nonegint()) -> usd().
get_gb_cost_per_block_at_datetime(DT, Height) ->
case Height >= ar_fork:height_2_5() of
true ->
{Dividend, Divisor} = get_gb_cost_per_year_at_datetime(DT, Height),
{Dividend, Divisor * ?BLOCKS_PER_YEAR};
false ->
get_gb_cost_per_year_at_datetime(DT, Height) / ?BLOCKS_PER_YEAR
end.
%% @doc Return the cost in USD of storing 1 GB per year. Estmimated from empirical data.
%% Assumes a year after 2019 inclusive. Uses data figures for 2018 and 2019.
%% Extrapolates the exponential decay curve k*e^(-at) to future years.
%% @end
-spec usd_p_gby(nonegint(), nonegint()) -> usd().
usd_p_gby(2018, Height) ->
{Dividend, Divisor} = ?USD_PER_GBY_2018,
case Height >= ar_fork:height_2_5() of
true ->
{Dividend, Divisor};
false ->
Dividend / Divisor
end;
usd_p_gby(2019, Height) ->
{Dividend, Divisor} = ?USD_PER_GBY_2019,
case Height >= ar_fork:height_2_5() of
true ->
{Dividend, Divisor};
false ->
Dividend / Divisor
end;
usd_p_gby(Y, Height) ->
case Height >= ar_fork:height_2_5() of
true ->
{KDividend, KDivisor} = ?USD_PER_GBY_2019,
{ADividend, ADivisor} = ?LN_PRICE_DECAY_ANNUAL,
T = Y - 2019,
P = ?TX_PRICE_NATURAL_EXPONENT_DECIMAL_FRACTION_PRECISION,
{EDividend, EDivisor} = ar_fraction:natural_exponent({ADividend * T, ADivisor}, P),
{EDividend * KDividend, EDivisor * KDivisor};
false ->
{Dividend, Divisor} = ?USD_PER_GBY_2019,
K = Dividend / Divisor,
{DecayDividend, DecayDivisor} = ?PRICE_DECAY_ANNUAL,
A = math:log(DecayDividend / DecayDivisor),
T = Y - 2019,
K * math:exp(A * T)
end.
%% @doc Return elapsed time as the fraction of the year
%% between Jun 30th of PrevY and Jun 30th of NextY.
%% @end
-spec fraction_of_year(nonegint(), nonegint(), datetime(), nonegint()) -> float() | fraction().
fraction_of_year(PrevY, NextY, {{Y, Mo, D}, {H, Mi, S}}, Height) ->
Start = calendar:datetime_to_gregorian_seconds({{PrevY, 6, 30}, {23, 59, 59}}),
Now = calendar:datetime_to_gregorian_seconds({{Y, Mo, D}, {H, Mi, S}}),
End = calendar:datetime_to_gregorian_seconds({{NextY, 6, 30}, {23, 59, 59}}),
case Height >= ar_fork:height_2_5() of
true ->
{Now - Start, End - Start};
false ->
(Now - Start) / (End - Start)
end.
%% TODO Use calendar:system_time_to_universal_time/2 in Erlang OTP-21.
system_time_to_universal_time(Time, TimeUnit) ->
Seconds = erlang:convert_time_unit(Time, TimeUnit, seconds),
DaysFrom0To1970 = 719528,
SecondsPerDay = 86400,
calendar:gregorian_seconds_to_datetime(Seconds + (DaysFrom0To1970 * SecondsPerDay)).
recalculate_usd_to_ar_rate2(#block{ height = PrevHeight } = B) ->
case is_price_adjustment_height(PrevHeight + 1) of
false ->
{B#block.usd_to_ar_rate, B#block.scheduled_usd_to_ar_rate};
true ->
Fork_2_6 = ar_fork:height_2_6(),
true = PrevHeight + 1 /= Fork_2_6,
case PrevHeight + 1 > Fork_2_6 of
true ->
%% Keep the rate fixed after the 2.6 fork till the transition to the
%% new pricing scheme ends. Then it won't be used any longer.
{B#block.scheduled_usd_to_ar_rate, B#block.scheduled_usd_to_ar_rate};
false ->
recalculate_usd_to_ar_rate3(B)
end
end.
recalculate_usd_to_ar_rate3(#block{ height = PrevHeight, diff = Diff } = B) ->
Height = PrevHeight + 1,
InitialDiff = ar_retarget:switch_to_linear_diff(?INITIAL_USD_TO_AR_DIFF(Height)()),
MaxDiff = ?MAX_DIFF,
InitialRate = ?INITIAL_USD_TO_AR(Height)(),
{Dividend, Divisor} = InitialRate,
ScheduledRate = {Dividend * (MaxDiff - Diff), Divisor * (MaxDiff - InitialDiff)},
Rate = B#block.scheduled_usd_to_ar_rate,
MaxAdjustmentUp = ar_fraction:multiply(Rate, ?USD_TO_AR_MAX_ADJUSTMENT_UP_MULTIPLIER),
MaxAdjustmentDown = ar_fraction:multiply(Rate, ?USD_TO_AR_MAX_ADJUSTMENT_DOWN_MULTIPLIER),
CappedScheduledRate = ar_fraction:reduce(ar_fraction:maximum(
ar_fraction:minimum(ScheduledRate, MaxAdjustmentUp), MaxAdjustmentDown),
?USD_TO_AR_FRACTION_REDUCTION_LIMIT),
?LOG_DEBUG([{event, recalculated_rate},
{new_rate, ar_util:safe_divide(element(1, Rate), element(2, Rate))},
{new_scheduled_rate, ar_util:safe_divide(element(1, CappedScheduledRate),
element(2, CappedScheduledRate))},
{new_scheduled_rate_without_capping,
ar_util:safe_divide(element(1, ScheduledRate), element(2, ScheduledRate))},
{max_adjustment_up, ar_util:safe_divide(element(1, MaxAdjustmentUp),
element(2,MaxAdjustmentUp))},
{max_adjustment_down, ar_util:safe_divide(element(1, MaxAdjustmentDown),
element(2,MaxAdjustmentDown))}]),
{Rate, CappedScheduledRate}.
%%%===================================================================
%%% Tests.
%%%===================================================================
get_gb_cost_per_year_at_datetime_is_monotone_test_() ->
[
ar_test_fork:test_on_fork(
height_2_5, infinity, fun test_get_gb_cost_per_year_at_datetime_is_monotone/0
) | [
ar_test_fork:test_on_fork(
height_2_5, Height, fun test_get_gb_cost_per_year_at_datetime_is_monotone/0
)
|| Height <- lists:seq(0, 20)
]
].
test_get_gb_cost_per_year_at_datetime_is_monotone() ->
InitialDT = {{2019, 1, 1}, {0, 0, 0}},
FollowingDTs = [
{{2019, 1, 1}, {10, 0, 0}},
{{2019, 6, 15}, {0, 0, 0}},
{{2019, 6, 29}, {23, 59, 59}},
{{2019, 6, 30}, {0, 0, 0}},
{{2019, 6, 30}, {23, 59, 59}},
{{2019, 7, 1}, {0, 0, 0}},
{{2019, 12, 31}, {23, 59, 59}},
{{2020, 1, 1}, {0, 0, 0}},
{{2020, 1, 2}, {0, 0, 0}},
{{2020, 10, 1}, {0, 0, 0}},
{{2020, 12, 31}, {23, 59, 59}},
{{2021, 1, 1}, {0, 0, 0}},
{{2021, 2, 1}, {0, 0, 0}},
{{2021, 12, 31}, {23, 59, 59}},
{{2022, 1, 1}, {0, 0, 0}},
{{2022, 6, 29}, {23, 59, 59}},
{{2022, 6, 30}, {0, 0, 0}},
{{2050, 3, 1}, {10, 10, 10}},
{{2100, 2, 1}, {0, 0, 0}}
],
lists:foldl(
fun(CurrDT, {PrevDT, PrevHeight}) ->
CurrCost = get_gb_cost_per_year_at_datetime(CurrDT, PrevHeight + 1),
PrevCost = get_gb_cost_per_year_at_datetime(PrevDT, PrevHeight),
assert_less_than_or_equal_to(CurrCost, PrevCost),
{CurrDT, PrevHeight + 1}
end,
{InitialDT, 0},
FollowingDTs
).
assert_less_than_or_equal_to(X1, X2) when is_number(X1), is_number(X2) ->
?assert(X1 =< X2, io_lib:format("~p is bigger than ~p", [X1, X2]));
assert_less_than_or_equal_to({Dividend1, Divisor1} = X1, X2) when is_number(X2) ->
?assert((Dividend1 div Divisor1) =< X2, io_lib:format("~p is bigger than ~p", [X1, X2]));
assert_less_than_or_equal_to({Dividend1, Divisor1} = X1, {Dividend2, Divisor2} = X2) ->
?assert(Dividend1 * Divisor2 =< Dividend2 * Divisor1,
io_lib:format("~p is bigger than ~p", [X1, X2])).