fix: scale price ratio correctly when fee token decimals exceed 18

.github/workflows/token-price-oracle.yml

@@ -0,0 +1,36 @@
+name: Token-price-oracle
+
+on:
+    push:
+        branches:
+            - main
+        paths:
+            - "token-price-oracle/**"
+            - ".github/workflows/token-price-oracle.yml"
+    pull_request:
+        paths:
+            - "token-price-oracle/**"
+            - ".github/workflows/token-price-oracle.yml"
+
+permissions:
+    contents: read
+
+defaults:
+    run:
+        working-directory: "token-price-oracle"
+
+jobs:
+    test:
+        runs-on: ubuntu-latest
+        steps:
+            - uses: actions/checkout@v4
+              with:
+                  persist-credentials: false
+            - name: Install Go
+              uses: actions/setup-go@v5
+              with:
+                  go-version: 1.24.x
+            - name: Run build
+              run: make build
+            - name: Run tests
+              run: make test

token-price-oracle/updater/token_price.go

@@ -356,10 +356,15 @@ func (u *PriceUpdater) calculatePriceRatioWithInfo(tokenID uint16, tokenPrice *c
 	priceRatio.Mul(priceRatio, tokenScaleFloat)
 
 	// Step 3: Multiply by 10^(18 - tokenDecimals)
-	// ETH has 18 decimals, so we need to adjust for token decimals
-	decimalAdjustment := new(big.Int).Exp(big.NewInt(10), big.NewInt(int64(18-tokenDecimals)), nil)
-	decimalAdjustmentFloat := new(big.Float).SetInt(decimalAdjustment)
-	priceRatio.Mul(priceRatio, decimalAdjustmentFloat)
+	// ETH has 18 decimals, so we need to adjust for token decimals. tokenDecimals
+	// is uint8, so subtract as int64; big.Int.Exp yields 1 for a negative exponent,
+	// so tokens with more than 18 decimals divide by 10^(tokenDecimals-18) instead.
+	decimalExponent := int64(18) - int64(tokenDecimals)
+	if decimalExponent < 0 {
+		priceRatio.Quo(priceRatio, new(big.Float).SetInt(new(big.Int).Exp(big.NewInt(10), big.NewInt(-decimalExponent), nil)))
+	} else {
+		priceRatio.Mul(priceRatio, new(big.Float).SetInt(new(big.Int).Exp(big.NewInt(10), big.NewInt(decimalExponent), nil)))
+	}
 
 	// Step 4: Finally divide by ethPriceUSD
 	priceRatio.Quo(priceRatio, tokenPrice.EthPriceUSD)

token-price-oracle/updater/token_price_test.go

@@ -0,0 +1,34 @@
+package updater
+
+import (
+	"math/big"
+	"testing"
+
+	"morph-l2/token-price-oracle/client"
+)
+
+func TestCalculatePriceRatioScalesDownDecimalsAbove18(t *testing.T) {
+	updater := &PriceUpdater{}
+	price := &client.TokenPrice{
+		TokenID:       1,
+		Symbol:        "TOKEN24",
+		TokenPriceUSD: big.NewFloat(1),
+		EthPriceUSD:   big.NewFloat(0.5),
+	}
+	info := &TokenInfo{
+		Decimals: 24,
+		Scale:    big.NewInt(1_000_000),
+		IsActive: true,
+	}
+
+	got, err := updater.calculatePriceRatioWithInfo(1, price, info)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// 1e6 * (1 USD / 0.5 USD per ETH) * 1e(18-24) = 2.
+	// A uint8 subtraction would wrap to 250 and scale by 1e250 instead.
+	if got.Cmp(big.NewInt(2)) != 0 {
+		t.Fatalf("price ratio = %s, want 2", got)
+	}
+}