From 177d56165131d0b4c272db6a11bc77c4ed1db6b7 Mon Sep 17 00:00:00 2001
From: pahor167 <47992132+pahor167@users.noreply.github.com>
Date: Mon, 19 Feb 2024 14:18:29 +0100
Subject: [PATCH 1/2] Round up of debit

---
 .../contracts-0.8/stability/FeeCurrencyAdapter.sol        | 2 +-
 .../protocol/test-sol/stability/FeeCurrencyAdapter.t.sol  | 8 ++++----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/packages/protocol/contracts-0.8/stability/FeeCurrencyAdapter.sol b/packages/protocol/contracts-0.8/stability/FeeCurrencyAdapter.sol
index ace1dc45490..33f0aae0b3a 100644
--- a/packages/protocol/contracts-0.8/stability/FeeCurrencyAdapter.sol
+++ b/packages/protocol/contracts-0.8/stability/FeeCurrencyAdapter.sol
@@ -162,7 +162,7 @@ contract FeeCurrencyAdapter is Initializable, CalledByVm, IFeeCurrencyAdapter {
   }
 
   function downscale(uint256 value) internal view returns (uint256) {
-    return value / digitDifference;
+    return (value + digitDifference - 1) / digitDifference;
   }
 
   function _setAdaptedToken(address _adaptedToken) internal virtual {
diff --git a/packages/protocol/test-sol/stability/FeeCurrencyAdapter.t.sol b/packages/protocol/test-sol/stability/FeeCurrencyAdapter.t.sol
index 87991fb133e..d5447d77fb4 100644
--- a/packages/protocol/test-sol/stability/FeeCurrencyAdapter.t.sol
+++ b/packages/protocol/test-sol/stability/FeeCurrencyAdapter.t.sol
@@ -183,7 +183,7 @@ contract FeeCurrencyAdapter_DebitGasFees is FeeCurrencyAdapterTest {
   function test_ShouldRevert_WhenScaledDebitValueIs0() public {
     vm.expectRevert("Scaled debit value must be > 0.");
     vm.prank(address(0));
-    feeCurrencyAdapter.debitGasFees(address(this), 1e7);
+    feeCurrencyAdapter.debitGasFees(address(this), 0);
   }
 
   function test_ShouldDebitCorrectAmount_WhenExpectedDigitsOnlyOneBigger() public {
@@ -373,9 +373,9 @@ contract FeeCurrencyAdapter_UpscaleAndDownScaleTests is FeeCurrencyAdapterTest {
   }
 
   function test_ShouldReturn0_WhenSmallEnough() public {
-    assertEq(feeCurrencyAdapter.downscaleVisible(1), 0);
-    assertEq(feeCurrencyAdapter.downscaleVisible(1e6 - 1), 0);
-    assertEq(feeCurrencyAdapter.downscaleVisible(1e12 - 1), 0);
+    assertEq(feeCurrencyAdapter.downscaleVisible(1), 1);
+    assertEq(feeCurrencyAdapter.downscaleVisible(1e6 - 1), 1);
+    assertEq(feeCurrencyAdapter.downscaleVisible(1e12 - 1), 1);
   }
 }
 

From 54de1f3f48f7a66817927e2c292004797f2742fc Mon Sep 17 00:00:00 2001
From: pahor167 <47992132+pahor167@users.noreply.github.com>
Date: Tue, 20 Feb 2024 10:50:11 +0100
Subject: [PATCH 2/2] PR comments

---
 .../contracts-0.8/stability/FeeCurrencyAdapter.sol     | 10 ++++++++++
 .../test-sol/stability/FeeCurrencyAdapter.t.sol        |  2 +-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/packages/protocol/contracts-0.8/stability/FeeCurrencyAdapter.sol b/packages/protocol/contracts-0.8/stability/FeeCurrencyAdapter.sol
index 33f0aae0b3a..fc19782e5c8 100644
--- a/packages/protocol/contracts-0.8/stability/FeeCurrencyAdapter.sol
+++ b/packages/protocol/contracts-0.8/stability/FeeCurrencyAdapter.sol
@@ -161,6 +161,16 @@ contract FeeCurrencyAdapter is Initializable, CalledByVm, IFeeCurrencyAdapter {
     return value * digitDifference;
   }
 
+  /**
+   * @notice Downscales value to the adapted token's native digits.
+   * @dev Downscale is rounding up in favour of protocol. User possibly can pay a bit more than expected (up to 1 unit of a token).
+   * Example:
+   * USDC has 6 decimals and in such case user can pay up to 0.000001 USDC more than expected.
+   * WBTC (currently not supported by Celo chain as fee currency) has 8 decimals and in such case user can pay up to 0.00000001 WBTC more than expected.
+   * Considering the current price of WBTC, it's less than 0.0005 USD. Even when WBTC price would be 1 mil USD, it's still would be only 0.01 USD.
+   * In general it is a very small amount and it is acceptable to round up in favor of the protocol.
+   * @param value The value to downscale. 
+   */
   function downscale(uint256 value) internal view returns (uint256) {
     return (value + digitDifference - 1) / digitDifference;
   }
diff --git a/packages/protocol/test-sol/stability/FeeCurrencyAdapter.t.sol b/packages/protocol/test-sol/stability/FeeCurrencyAdapter.t.sol
index d5447d77fb4..1cc122a8c0b 100644
--- a/packages/protocol/test-sol/stability/FeeCurrencyAdapter.t.sol
+++ b/packages/protocol/test-sol/stability/FeeCurrencyAdapter.t.sol
@@ -372,7 +372,7 @@ contract FeeCurrencyAdapter_UpscaleAndDownScaleTests is FeeCurrencyAdapterTest {
     assertEq(feeCurrencyAdapter.downscaleVisible(1e24), 1e12);
   }
 
-  function test_ShouldReturn0_WhenSmallEnough() public {
+  function test_ShouldReturn1_WhenSmallEnoughAndRoundingUp() public {
     assertEq(feeCurrencyAdapter.downscaleVisible(1), 1);
     assertEq(feeCurrencyAdapter.downscaleVisible(1e6 - 1), 1);
     assertEq(feeCurrencyAdapter.downscaleVisible(1e12 - 1), 1);