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token-swap: Improve pool token supply on initialization, deposit, and…
… withdrawal (solana-labs#508) * token-swap: Add token supply in invariant calculation * Refactor state classes into curve components for future use * Align pool initialization with Uniswap using geometric mean of token amounts * Fix deposit and withdraw instruction to work as a proportion of pool tokens * Add math utilities to calculate the geometric mean with u64 * Improve variable names * Use a fixed starting pool size * Run cargo fmt * Update js tests with new pool numbers * Run linting * Remove math * Fix BN type issues found by flow
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,165 @@ | ||
| //! Swap calculations and curve implementations | ||
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|
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| /// Initial amount of pool tokens for swap contract, hard-coded to something | ||
| /// "sensible" given a maximum of u64. | ||
| /// Note that on Ethereum, Uniswap uses the geometric mean of all provided | ||
| /// input amounts, and Balancer uses 100 * 10 ^ 18. | ||
| pub const INITIAL_SWAP_POOL_AMOUNT: u64 = 1_000_000_000; | ||
|
|
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| /// Encodes all results of swapping from a source token to a destination token | ||
| pub struct SwapResult { | ||
| /// New amount of source token | ||
| pub new_source_amount: u64, | ||
| /// New amount of destination token | ||
| pub new_destination_amount: u64, | ||
| /// Amount of destination token swapped | ||
| pub amount_swapped: u64, | ||
| } | ||
|
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||
| impl SwapResult { | ||
| /// SwapResult for swap from one currency into another, given pool information | ||
| /// and fee | ||
| pub fn swap_to( | ||
| source_amount: u64, | ||
| swap_source_amount: u64, | ||
| swap_destination_amount: u64, | ||
| fee_numerator: u64, | ||
| fee_denominator: u64, | ||
| ) -> Option<SwapResult> { | ||
| let invariant = swap_source_amount.checked_mul(swap_destination_amount)?; | ||
| let new_source_amount = swap_source_amount.checked_add(source_amount)?; | ||
| let new_destination_amount = invariant.checked_div(new_source_amount)?; | ||
| let remove = swap_destination_amount.checked_sub(new_destination_amount)?; | ||
| let fee = remove | ||
| .checked_mul(fee_numerator)? | ||
| .checked_div(fee_denominator)?; | ||
| let new_destination_amount = new_destination_amount.checked_add(fee)?; | ||
| let amount_swapped = remove.checked_sub(fee)?; | ||
| Some(SwapResult { | ||
| new_source_amount, | ||
| new_destination_amount, | ||
| amount_swapped, | ||
| }) | ||
| } | ||
| } | ||
|
|
||
| /// The Uniswap invariant calculator. | ||
| pub struct ConstantProduct { | ||
| /// Token A | ||
| pub token_a: u64, | ||
| /// Token B | ||
| pub token_b: u64, | ||
| /// Fee numerator | ||
| pub fee_numerator: u64, | ||
| /// Fee denominator | ||
| pub fee_denominator: u64, | ||
| } | ||
|
|
||
| impl ConstantProduct { | ||
| /// Swap token a to b | ||
| pub fn swap_a_to_b(&mut self, token_a: u64) -> Option<u64> { | ||
| let result = SwapResult::swap_to( | ||
| token_a, | ||
| self.token_a, | ||
| self.token_b, | ||
| self.fee_numerator, | ||
| self.fee_denominator, | ||
| )?; | ||
| self.token_a = result.new_source_amount; | ||
| self.token_b = result.new_destination_amount; | ||
| Some(result.amount_swapped) | ||
| } | ||
|
|
||
| /// Swap token b to a | ||
| pub fn swap_b_to_a(&mut self, token_b: u64) -> Option<u64> { | ||
| let result = SwapResult::swap_to( | ||
| token_b, | ||
| self.token_b, | ||
| self.token_a, | ||
| self.fee_numerator, | ||
| self.fee_denominator, | ||
| )?; | ||
| self.token_b = result.new_source_amount; | ||
| self.token_a = result.new_destination_amount; | ||
| Some(result.amount_swapped) | ||
| } | ||
| } | ||
|
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||
| /// Conversions for pool tokens, how much to deposit / withdraw, along with | ||
| /// proper initialization | ||
| pub struct PoolTokenConverter { | ||
| /// Total supply | ||
| pub supply: u64, | ||
| /// Token A amount | ||
| pub token_a: u64, | ||
| /// Token B amount | ||
| pub token_b: u64, | ||
| } | ||
|
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||
| impl PoolTokenConverter { | ||
| /// Create a converter based on existing market information | ||
| pub fn new_existing(supply: u64, token_a: u64, token_b: u64) -> Self { | ||
| Self { | ||
| supply, | ||
| token_a, | ||
| token_b, | ||
| } | ||
| } | ||
|
|
||
| /// Create a converter for a new pool token, no supply present yet. | ||
| /// According to Uniswap, the geometric mean protects the pool creator | ||
| /// in case the initial ratio is off the market. | ||
| pub fn new_pool(token_a: u64, token_b: u64) -> Self { | ||
| let supply = INITIAL_SWAP_POOL_AMOUNT; | ||
| Self { | ||
| supply, | ||
| token_a, | ||
| token_b, | ||
| } | ||
| } | ||
|
|
||
| /// A tokens for pool tokens | ||
| pub fn token_a_rate(&self, pool_tokens: u64) -> Option<u64> { | ||
| pool_tokens | ||
| .checked_mul(self.token_a)? | ||
| .checked_div(self.supply) | ||
| } | ||
|
|
||
| /// B tokens for pool tokens | ||
| pub fn token_b_rate(&self, pool_tokens: u64) -> Option<u64> { | ||
| pool_tokens | ||
| .checked_mul(self.token_b)? | ||
| .checked_div(self.supply) | ||
| } | ||
| } | ||
|
|
||
| #[cfg(test)] | ||
| mod tests { | ||
| use super::*; | ||
|
|
||
| #[test] | ||
| fn initial_pool_amount() { | ||
| let token_converter = PoolTokenConverter::new_pool(1, 5); | ||
| assert_eq!(token_converter.supply, INITIAL_SWAP_POOL_AMOUNT); | ||
| } | ||
|
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||
| fn check_pool_token_a_rate( | ||
| token_a: u64, | ||
| token_b: u64, | ||
| deposit: u64, | ||
| supply: u64, | ||
| expected: Option<u64>, | ||
| ) { | ||
| let calculator = PoolTokenConverter::new_existing(supply, token_a, token_b); | ||
| assert_eq!(calculator.token_a_rate(deposit), expected); | ||
| } | ||
|
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||
| #[test] | ||
| fn issued_tokens() { | ||
| check_pool_token_a_rate(2, 50, 5, 10, Some(1)); | ||
| check_pool_token_a_rate(10, 10, 5, 10, Some(5)); | ||
| check_pool_token_a_rate(5, 100, 5, 10, Some(2)); | ||
| check_pool_token_a_rate(5, u64::MAX, 5, 10, Some(2)); | ||
| check_pool_token_a_rate(u64::MAX, u64::MAX, 5, 10, None); | ||
| } | ||
| } |
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