fix: usd precision

Author: helciofranco

.changeset/giant-frogs-develop.md

@@ -0,0 +1,5 @@
+---
+"fuels-wallet": patch
+---
+
+fix: improve precision handling for USD conversion with really low rates (e.g. 0.0000007427)

packages/app/src/systems/Core/utils/convertToUsd.test.ts

@@ -1,4 +1,4 @@
-import { DECIMAL_FUEL, bn } from 'fuels';
+import { DECIMAL_FUEL, DECIMAL_WEI, bn } from 'fuels';
 import { convertToUsd } from './convertToUsd';
 
 const MOCK_ETH_RATE = 2742.15;
@@ -56,6 +56,26 @@ describe('Convert to USD', () => {
     expect(value).toBe(24699091436.38);
   });
 
+  it('should be able to handle large amounts with high precision and regular rate', () => {
+    const { formatted, value } = convertToUsd(
+      bn('123456789999999999900000000000000001'),
+      DECIMAL_WEI,
+      MOCK_ETH_RATE
+    );
+    expect(formatted).toBe('$338,537,036,698,499,999,725.78');
+    expect(value).toBe(338537036698500000000);
+  });
+
+  it('should be able to handle large amounts with high precision decimal and low rate', () => {
+    const { formatted, value } = convertToUsd(
+      bn('123456789999999999900000000000000001'),
+      DECIMAL_WEI,
+      MOCK_REALLY_LOW_RATE
+    );
+    expect(formatted).toBe('$91,691,357,932.99');
+    expect(value).toBe(91691357932.99);
+  });
+
   it('should be able to handle lower rates', () => {
     const { formatted, value } = convertToUsd(
       bn(100_000_000_000),

packages/app/src/systems/Core/utils/convertToUsd.ts

@@ -10,8 +10,9 @@ function countDecimals(value: number): number {
 
   // Handle scientific notation
   if (str.includes('e-')) {
-    const [, exp] = str.split('e-');
-    return Number(exp);
+    const [nonExp, exp] = str.split('e-');
+    const [, decimals] = nonExp.split('.');
+    return Number(exp) + decimals.length;
   }
   return str.split('.')[1]?.length || 0;
 }
@@ -31,11 +32,11 @@ export function convertToUsd(
   const rateDecimals = countDecimals(rate);
   const targetPrecision = getTargetPrecision(rateDecimals, decimals);
 
-  // Convert the rate to a fixed-point integer (truncated to avoid rounding errors).
-  // If the amount has more decimals than the rate, we need to add zeros to the rate.
-  // If not, we don't need to do anything.
-  const ratePrecision = 10 ** targetPrecision;
-  const rateFixed = Math.trunc(rate * ratePrecision);
+  // Get how many decimal places we need to apply to the rate to match the amount precision.
+  // Usually the amount has more decimals than the rate, so we need to add zeros to the rate.
+  const ratePrecision = Math.max(decimals - rateDecimals, 0);
+  const rateUnits = bn.parseUnits(rate.toFixed(rateDecimals), rateDecimals);
+  const rateFixed = rateUnits.mul(bn(10).pow(ratePrecision));
 
   // Get how many decimal places we need to apply to the amount to match the rate precision.
   // Sometimes the rate has more decimals than the amount, so we need to add zeros to the amount.