Stable fees (#209)

dex/Cargo.lock

@@ -982,7 +982,7 @@ dependencies = [
 
 [[package]]
 name = "serum_dex"
-version = "0.5.1"
+version = "0.5.2"
 dependencies = [
  "arbitrary",
  "arrayref",

dex/src/fees.rs

@@ -1,9 +1,19 @@
 use num_enum::{IntoPrimitive, TryFromPrimitive};
+use solana_program::pubkey::Pubkey;
 use std::convert::TryInto;
 
 #[cfg(test)]
 use proptest_derive::Arbitrary;
 
+mod stable_markets {
+    pub mod usdt_usdc {
+        solana_program::declare_id!("77quYg4MGneUdjgXCunt9GgM1usmrxKY31twEy3WHwcS");
+    }
+    pub mod msol_sol {
+        solana_program::declare_id!("5cLrMai1DsLRYc1Nio9qMTicsWtvzjzZfJPXyAoF4t1Z");
+    }
+}
+
 #[derive(Copy, Clone, IntoPrimitive, TryFromPrimitive, Debug)]
 #[cfg_attr(test, derive(Arbitrary))]
 #[repr(u8)]
@@ -15,6 +25,7 @@ pub enum FeeTier {
     SRM5,
     SRM6,
     MSRM,
+    Stable,
 }
 
 #[repr(transparent)]
@@ -67,8 +78,13 @@ const fn rebate_tenth_of_bps(tenth_of_bps: u64) -> U64F64 {
 
 impl FeeTier {
     #[inline]
-    pub fn from_srm_and_msrm_balances(srm_held: u64, msrm_held: u64) -> FeeTier {
+    pub fn from_srm_and_msrm_balances(market: &Pubkey, srm_held: u64, msrm_held: u64) -> FeeTier {
         let one_srm = 1_000_000;
+
+        if market == &stable_markets::usdt_usdc::ID || market == &stable_markets::msol_sol::ID {
+            return FeeTier::Stable;
+        }
+
         match () {
             () if msrm_held >= 1 => FeeTier::MSRM,
             () if srm_held >= one_srm * 1_000_000 => FeeTier::SRM6,
@@ -95,6 +111,7 @@ impl FeeTier {
             SRM5 => fee_tenth_of_bps(34),
             SRM6 => fee_tenth_of_bps(32),
             MSRM => fee_tenth_of_bps(30),
+            Stable => fee_tenth_of_bps(10),
         }
     }
 

dex/src/matching.rs

@@ -7,6 +7,7 @@ use proptest_derive::Arbitrary;
 use serde::{Deserialize, Serialize};
 #[cfg(feature = "program")]
 use solana_program::msg;
+use solana_program::pubkey::Pubkey;
 
 use crate::critbit::SlabTreeError;
 use crate::error::{DexErrorCode, DexResult, SourceFileId};
@@ -226,12 +227,9 @@ struct OrderRemaining {
 impl<'ob> OrderBookState<'ob> {
     fn new_order(
         &mut self,
-
         params: NewOrderParams,
         event_q: &mut EventQueue,
-
         proceeds: &mut RequestProceeds,
-
         limit: &mut u16,
     ) -> DexResult<Option<OrderRemaining>> {
         let NewOrderParams {

dex/src/state.rs

@@ -547,16 +547,26 @@ impl MarketState {
         bytes_of_mut(&mut aligned_data).copy_from_slice(&data[..72]);
         let (mint, owner, &[balance]) = array_refs![&aligned_data, 4, 4, 1];
 
+        let market_addr = self.pubkey();
+
         check_assert_eq!(owner, expected_owner)?;
         if mint == &srm_token::ID.to_aligned_bytes() {
-            return Ok(FeeTier::from_srm_and_msrm_balances(balance, 0));
+            return Ok(FeeTier::from_srm_and_msrm_balances(
+                &market_addr,
+                balance,
+                0,
+            ));
         }
 
         if mint == &msrm_token::ID.to_aligned_bytes() {
-            return Ok(FeeTier::from_srm_and_msrm_balances(0, balance));
+            return Ok(FeeTier::from_srm_and_msrm_balances(
+                &market_addr,
+                0,
+                balance,
+            ));
         }
 
-        Ok(FeeTier::from_srm_and_msrm_balances(0, 0))
+        Ok(FeeTier::from_srm_and_msrm_balances(&market_addr, 0, 0))
     }
 
     fn check_enabled(&self) -> DexResult {