fix(token-swap): compute amm math in u128 to avoid I64F64 overflow

tokens/token-swap/anchor/programs/token-swap/Cargo.toml

@@ -22,7 +22,6 @@ custom-panic = []
 [dependencies]
 anchor-lang = { version = "1.0.2", features = ["init-if-needed"] }
 anchor-spl = { version = "1.0.2", features = ["metadata"] }
-fixed = "1.27.0"
 
 [lints.rust]
 unexpected_cfgs = { level = "warn", check-cfg = ['cfg(target_os, values("solana"))'] }

tokens/token-swap/anchor/programs/token-swap/src/instructions/deposit_liquidity.rs

@@ -3,7 +3,6 @@ use anchor_spl::{
     associated_token::AssociatedToken,
     token::{self, Mint, MintTo, Token, TokenAccount, Transfer},
 };
-use fixed::types::I64F64;
 
 use crate::{
     constants::{AUTHORITY_SEED, LIQUIDITY_SEED, MINIMUM_LIQUIDITY},
@@ -64,12 +63,12 @@ pub fn deposit_liquidity(
         }
     };
 
-    // Computing the amount of liquidity about to be deposited
-    let mut liquidity = I64F64::from_num(amount_a)
-        .checked_mul(I64F64::from_num(amount_b))
+    // Computing the amount of liquidity about to be deposited.
+    // Multiply in u128 so the product of two u64 amounts cannot overflow.
+    let mut liquidity = (amount_a as u128)
+        .checked_mul(amount_b as u128)
         .unwrap()
-        .sqrt()
-        .to_num::<u64>();
+        .isqrt() as u64;
 
     // Lock some minimum liquidity on the first deposit
     if pool_creation {

tokens/token-swap/anchor/programs/token-swap/src/instructions/swap_exact_tokens_for_tokens.rs

@@ -3,7 +3,6 @@ use anchor_spl::{
     associated_token::AssociatedToken,
     token::{self, Mint, Token, TokenAccount, Transfer},
 };
-use fixed::types::I64F64;
 
 use crate::{
     constants::AUTHORITY_SEED,
@@ -32,28 +31,21 @@ pub fn swap_exact_tokens_for_tokens(
 
     let pool_a = &ctx.accounts.pool_account_a;
     let pool_b = &ctx.accounts.pool_account_b;
+    // Constant-product output, computed in u128 so taxed_input * pool amount
+    // cannot overflow.
     let output = if swap_a {
-        I64F64::from_num(taxed_input)
-            .checked_mul(I64F64::from_num(pool_b.amount))
+        (taxed_input as u128)
+            .checked_mul(pool_b.amount as u128)
             .unwrap()
-            .checked_div(
-                I64F64::from_num(pool_a.amount)
-                    .checked_add(I64F64::from_num(taxed_input))
-                    .unwrap(),
-            )
+            .checked_div((pool_a.amount as u128).checked_add(taxed_input as u128).unwrap())
             .unwrap()
     } else {
-        I64F64::from_num(taxed_input)
-            .checked_mul(I64F64::from_num(pool_a.amount))
+        (taxed_input as u128)
+            .checked_mul(pool_a.amount as u128)
             .unwrap()
-            .checked_div(
-                I64F64::from_num(pool_b.amount)
-                    .checked_add(I64F64::from_num(taxed_input))
-                    .unwrap(),
-            )
+            .checked_div((pool_b.amount as u128).checked_add(taxed_input as u128).unwrap())
             .unwrap()
-    }
-    .to_num::<u64>();
+    } as u64;
 
     if output < min_output_amount {
         return err!(TutorialError::OutputTooSmall);

tokens/token-swap/anchor/programs/token-swap/src/instructions/withdraw_liquidity.rs

@@ -3,7 +3,6 @@ use anchor_spl::{
     associated_token::AssociatedToken,
     token::{self, Burn, Mint, Token, TokenAccount, Transfer},
 };
-use fixed::types::I64F64;
 
 use crate::{
     constants::{AUTHORITY_SEED, LIQUIDITY_SEED, MINIMUM_LIQUIDITY},
@@ -21,16 +20,13 @@ pub fn withdraw_liquidity(ctx: Context<WithdrawLiquidity>, amount: u64) -> Resul
     ];
     let signer_seeds = &[&authority_seeds[..]];
 
-    // Transfer tokens from the pool
-    let amount_a = I64F64::from_num(amount)
-        .checked_mul(I64F64::from_num(ctx.accounts.pool_account_a.amount))
+    // Transfer tokens from the pool. Compute in u128 so amount * pool balance
+    // cannot overflow.
+    let amount_a = (amount as u128)
+        .checked_mul(ctx.accounts.pool_account_a.amount as u128)
         .unwrap()
-        .checked_div(I64F64::from_num(
-            ctx.accounts.mint_liquidity.supply + MINIMUM_LIQUIDITY,
-        ))
-        .unwrap()
-        .floor()
-        .to_num::<u64>();
+        .checked_div(ctx.accounts.mint_liquidity.supply as u128 + MINIMUM_LIQUIDITY as u128)
+        .unwrap() as u64;
     token::transfer(
         CpiContext::new_with_signer(
             ctx.accounts.token_program.key(),
@@ -44,15 +40,11 @@ pub fn withdraw_liquidity(ctx: Context<WithdrawLiquidity>, amount: u64) -> Resul
         amount_a,
     )?;
 
-    let amount_b = I64F64::from_num(amount)
-        .checked_mul(I64F64::from_num(ctx.accounts.pool_account_b.amount))
-        .unwrap()
-        .checked_div(I64F64::from_num(
-            ctx.accounts.mint_liquidity.supply + MINIMUM_LIQUIDITY,
-        ))
+    let amount_b = (amount as u128)
+        .checked_mul(ctx.accounts.pool_account_b.amount as u128)
         .unwrap()
-        .floor()
-        .to_num::<u64>();
+        .checked_div(ctx.accounts.mint_liquidity.supply as u128 + MINIMUM_LIQUIDITY as u128)
+        .unwrap() as u64;
     token::transfer(
         CpiContext::new_with_signer(
             ctx.accounts.token_program.key(),

tokens/token-swap/anchor/programs/token-swap/src/lib.rs

@@ -6,7 +6,7 @@ mod instructions;
 mod state;
 
 // Set the correct key here
-declare_id!("AsGVFxWqEn8icRBFQApxJe68x3r9zvfSbmiEzYFATGYn");
+declare_id!("J1seUW7nGbsUeDQFBRe4bjC6c8ZRYKFqjV4CwiRSH18V");
 
 #[program]
 pub mod swap_example {