sdk: getTokenAmount uses divCeil (#371)

* sdk: getTokenAmount uses divCeil

* fix tests

* fix lint

* CHANGELOG

CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixes
 
 - ts-sdk: fix resolvePerpBankrupcty to work with all perp market indexes
+- ts-sdk: getTokenAmount uses divCeil ([#371](https://github.com/drift-labs/protocol-v2/pull/371))
 - program: allow limit orders to have explicit zero auction duration passed in params ([#373](https://github.com/drift-labs/protocol-v2/pull/373))
 
 ### Breaking

sdk/src/math/spotBalance.ts

@@ -21,6 +21,7 @@ import {
 } from './margin';
 import { OraclePriceData } from '../oracles/types';
 import { PERCENTAGE_PRECISION } from '../constants/numericConstants';
+import { divCeil } from './utils';
 
 export function getBalance(
 	tokenAmount: BN,
@@ -49,11 +50,16 @@ export function getTokenAmount(
 ): BN {
 	const precisionDecrease = TEN.pow(new BN(19 - spotMarket.decimals));
 
-	const cumulativeInterest = isVariant(balanceType, 'deposit')
-		? spotMarket.cumulativeDepositInterest
-		: spotMarket.cumulativeBorrowInterest;
-
-	return balanceAmount.mul(cumulativeInterest).div(precisionDecrease);
+	if (isVariant(balanceType, 'deposit')) {
+		return balanceAmount
+			.mul(spotMarket.cumulativeDepositInterest)
+			.div(precisionDecrease);
+	} else {
+		return divCeil(
+			balanceAmount.mul(spotMarket.cumulativeBorrowInterest),
+			precisionDecrease
+		);
+	}
 }
 
 export function getSignedTokenAmount(

sdk/src/math/utils.ts

@@ -1,4 +1,4 @@
-import { BN } from '../';
+import { BN, ONE, ZERO } from '../';
 
 export function clampBN(x: BN, min: BN, max: BN): BN {
 	return BN.max(min, BN.min(x, max));
@@ -21,3 +21,15 @@ export const squareRootBN = (n: BN): BN => {
 		return largeCand;
 	}
 };
+
+export const divCeil = (a: BN, b: BN): BN => {
+	const quotient = a.div(b);
+
+	const remainder = a.mod(b);
+
+	if (remainder.gt(ZERO)) {
+		return quotient.add(ONE);
+	} else {
+		return quotient;
+	}
+};

tests/liquidateSpotSocialLoss.ts

@@ -28,7 +28,7 @@ import {
 	createWSolTokenAccountForUser,
 	initializeSolSpotMarket,
 } from './testHelpers';
-import { BulkAccountLoader, isVariant, ONE } from '../sdk';
+import { BulkAccountLoader, isVariant } from '../sdk';
 
 describe('liquidate spot w/ social loss', () => {
 	const provider = anchor.AnchorProvider.local(undefined, {
@@ -288,7 +288,7 @@ describe('liquidate spot w/ social loss', () => {
 
 		const interestOfUpdate = currentDepositAmount.sub(depositAmountBefore);
 		console.log('interestOfUpdate:', interestOfUpdate.toString());
-		assert(interestOfUpdate.eq(ONE));
+		assert(interestOfUpdate.eq(ZERO));
 	});
 
 	it('resolve bankruptcy', async () => {

tests/spotDepositWithdraw.ts

@@ -669,9 +669,7 @@ describe('spot deposit and withdraw', () => {
 			userBalanceAfter.scaledBalance.toString()
 		);
 
-		assert(
-			expectedUserBalance.eq(userBalanceAfter.scaledBalance.add(new BN(1000)))
-		);
+		assert(expectedUserBalance.eq(userBalanceAfter.scaledBalance));
 		assert(isVariant(userBalanceAfter.balanceType, 'deposit'));
 
 		const expectedSpotMarketDepositBalance =
@@ -683,9 +681,7 @@ describe('spot deposit and withdraw', () => {
 		);
 
 		assert(
-			spotMarketAccount.depositBalance.eq(
-				expectedSpotMarketDepositBalance.sub(new BN(1000))
-			)
+			spotMarketAccount.depositBalance.eq(expectedSpotMarketDepositBalance)
 		);
 		assert(spotMarketAccount.borrowBalance.eq(ZERO));
 	});
@@ -780,7 +776,7 @@ describe('spot deposit and withdraw', () => {
 			expectedUserUSDCAmount.toString(),
 			userUSDCAmountAfter.toString()
 		);
-		assert(expectedUserUSDCAmount.eq(userUSDCAmountAfter.add(ONE)));
+		assert(expectedUserUSDCAmount.eq(userUSDCAmountAfter));
 
 		const userBalanceAfter = secondUserDriftClient.getSpotPosition(marketIndex);
 		assert(userBalanceAfter.scaledBalance.eq(ZERO));