Merge pull request #14 from blockworks-foundation/borrow_rounding

Fixed settle borrow rounding error
blockworks-foundation · Apr 22, 2021 · 896a3c6 · 896a3c6
2 parents bed8980 + a28d392
commit 896a3c6
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Showing 4 changed files with 18 additions and 16 deletions.
diff --git a/cli/Cargo.lock b/cli/Cargo.lock
diff --git a/program/Cargo.lock b/program/Cargo.lock
diff --git a/program/Cargo.toml b/program/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "mango"
-version = "0.2.4"
+version = "0.2.5"
 authors = ["blockworks"]
 edition = "2018"
 

diff --git a/program/src/processor.rs b/program/src/processor.rs
@@ -1548,21 +1548,23 @@ fn settle_borrow_unchecked(
     token_index: usize,
     quantity: u64
 ) -> MangoResult<()> {
-    let index: &MangoIndex = &mango_group.indexes[token_index];
-
-    let native_borrow = margin_account.get_native_borrow(index, token_index);
-    let native_deposit = margin_account.get_native_deposit(index, token_index);
-
-    let quantity = cmp::min(cmp::min(quantity, native_borrow), native_deposit);
-
-    let borr_settle = U64F64::from_num(quantity) / index.borrow;
-    let dep_settle = U64F64::from_num(quantity) / index.deposit;
-
-    checked_sub_deposit(mango_group, margin_account, token_index, dep_settle)?;
-    checked_sub_borrow(mango_group, margin_account, token_index, borr_settle)?;
+    let deposit_index = mango_group.indexes[token_index].deposit;
+    let borrow_index = mango_group.indexes[token_index].borrow;
+    let native_borrow: U64F64 = margin_account.borrows[token_index] * borrow_index;
+    let native_deposit: U64F64 = margin_account.deposits[token_index] * deposit_index;
+    let quantity = U64F64::from_num(quantity);
+
+    let quantity = min(quantity, native_deposit);
+    if quantity >= native_borrow {  // Reduce borrows to 0 to prevent rounding related dust
+        // NOTE: native_borrow / index.borrow is same as margin_account.borrows[token_index]
+        checked_sub_deposit(mango_group, margin_account, token_index, native_borrow / deposit_index)?;
+        checked_sub_borrow(mango_group, margin_account, token_index, margin_account.borrows[token_index])?;
+    } else {
+        checked_sub_deposit(mango_group, margin_account, token_index, quantity / deposit_index)?;
+        checked_sub_borrow(mango_group, margin_account, token_index, quantity / borrow_index)?;
+    }
 
     // No need to check collateralization ratio or deposits/borrows validity
-
     Ok(())
 
 }