From 04b6a37176f8be72c4cbe0f807994fffee303471 Mon Sep 17 00:00:00 2001
From: 0xbigz <83473873+0xbigz@users.noreply.github.com>
Date: Wed, 11 Dec 2024 13:59:34 -0500
Subject: [PATCH] program: bound-quote-reserve-divisor

---
 programs/drift/src/math/amm_spread.rs       | 11 ++++++--
 programs/drift/src/math/amm_spread/tests.rs | 30 +++++++++++++++++++++
 2 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/programs/drift/src/math/amm_spread.rs b/programs/drift/src/math/amm_spread.rs
index af929f6a4f..2f4e1abf44 100644
--- a/programs/drift/src/math/amm_spread.rs
+++ b/programs/drift/src/math/amm_spread.rs
@@ -486,8 +486,14 @@ pub fn calculate_spread_reserves(
     };
 
     let quote_asset_reserve_delta = if spread_with_offset.abs() > 1 {
-        let quote_reserve_divisor =
-            BID_ASK_SPREAD_PRECISION_I128 / (spread_with_offset / 2).cast::<i128>()?;
+        let mut quote_reserve_divisor =
+            (BID_ASK_SPREAD_PRECISION_I128 / (spread_with_offset / 2).cast::<i128>()?);
+
+        // ensure the divisor is not zero
+        if quote_reserve_divisor == 0 {
+            quote_reserve_divisor = if spread_with_offset > 0 { 1 } else { -1 };
+        }
+        
         market
             .amm
             .quote_asset_reserve
@@ -507,6 +513,7 @@ pub fn calculate_spread_reserves(
             .amm
             .quote_asset_reserve
             .safe_sub(quote_asset_reserve_delta.unsigned_abs())?
+            .max(1)
     };
 
     if market.contract_type == ContractType::Prediction {
diff --git a/programs/drift/src/math/amm_spread/tests.rs b/programs/drift/src/math/amm_spread/tests.rs
index 1d983ff1af..a88eedc8c0 100644
--- a/programs/drift/src/math/amm_spread/tests.rs
+++ b/programs/drift/src/math/amm_spread/tests.rs
@@ -189,6 +189,36 @@ mod test {
         assert_eq!(res, 0);
     }
 
+
+    #[test]
+    fn calculate_extreme_spread_tests() {
+        let amm = AMM {
+            base_asset_reserve: 2 * AMM_RESERVE_PRECISION,
+            quote_asset_reserve: 2 * AMM_RESERVE_PRECISION,
+            sqrt_k: 2 * AMM_RESERVE_PRECISION,
+            peg_multiplier: PEG_PRECISION,
+            long_spread:  (BID_ASK_SPREAD_PRECISION as u32) + 1000,
+            short_spread: (BID_ASK_SPREAD_PRECISION as u32) + 1000,
+            max_spread: (BID_ASK_SPREAD_PRECISION/2) as u32,
+            curve_update_intensity: 100,
+            ..AMM::default()
+        };
+
+        let mut market = PerpMarket {
+            amm,
+            ..PerpMarket::default()
+        };
+
+        let (bar_l, qar_l) = calculate_spread_reserves(&market, PositionDirection::Long).unwrap();
+        let (bar_s, qar_s) = calculate_spread_reserves(&market, PositionDirection::Short).unwrap();
+
+        assert_eq!(bar_s, 4000000000000000000);
+        assert_eq!(qar_s, 1);
+
+        assert_eq!(bar_l, 1000000000);
+        assert_eq!(qar_l, 4000000000);
+    }
+
     #[test]
     fn calculate_spread_tests() {
         let base_spread = 1000; // .1%