From 3e68ca02023df0ae417079e3e74fe23ec2476836 Mon Sep 17 00:00:00 2001
From: operagxoksana <operagxoksana@gmail.com>
Date: Thu, 23 Jul 2026 10:34:39 +0000
Subject: [PATCH] fix: FixedPointNumber.eq() used multiplication instead of
 exponentiation

When comparing two FixedPointNumber instances with different scales
where this.scale > value.scale, eq() scaled the operand with
value.value * BigInt(10) * (this.scale - value.scale) instead of
value.value * BigInt(10) ** (this.scale - value.scale).

lt/lte/gt/gte already use the correct ** form for both scale-mismatch
branches; only this one branch of eq() used * by mistake, e.g.:

  new FixedPointNumber(500, 2).eq(new FixedPointNumber(5, 0))
  // 5.00 vs 5 -> was false, should be true

FixedPointNumber has no external consumers yet, so there is no
actively exploited path in the current app - but it is a core
comparison primitive in src/architecture and any future
allowance/balance/permit-amount equality check built on top of it
would silently misbehave for mismatched decimals.

Adds src/architecture/__tests__/FixedPointNumber.test.ts covering both
scale-mismatch directions symmetrically, since only one direction was
broken.
---
 src/architecture/FixedPointNumber.ts          |  2 +-
 .../__tests__/FixedPointNumber.test.ts        | 35 +++++++++++++++++++
 2 files changed, 36 insertions(+), 1 deletion(-)
 create mode 100644 src/architecture/__tests__/FixedPointNumber.test.ts

diff --git a/src/architecture/FixedPointNumber.ts b/src/architecture/FixedPointNumber.ts
index a9a69d40d3..606fb70dd0 100644
--- a/src/architecture/FixedPointNumber.ts
+++ b/src/architecture/FixedPointNumber.ts
@@ -149,7 +149,7 @@ export class FixedPointNumber implements IFixedPointNumber {
   eq(value: FixedPointNumberValue): boolean {
     if (value instanceof FixedPointNumber) {
       if (this.scale > value.scale) {
-        return this.value === value.value * BigInt(10) * (this.scale - value.scale);
+        return this.value === value.value * BigInt(10) ** (this.scale - value.scale);
       }
       return this.value * BigInt(10) ** (value.scale - this.scale) === value.value;
     }
diff --git a/src/architecture/__tests__/FixedPointNumber.test.ts b/src/architecture/__tests__/FixedPointNumber.test.ts
new file mode 100644
index 0000000000..53bf2056d4
--- /dev/null
+++ b/src/architecture/__tests__/FixedPointNumber.test.ts
@@ -0,0 +1,35 @@
+import { FixedPointNumber } from '../FixedPointNumber';
+
+describe('FixedPointNumber.eq', () => {
+  it('returns true for equal values with the same scale', () => {
+    expect(new FixedPointNumber(500, 2).eq(new FixedPointNumber(500, 2))).toBe(true);
+  });
+
+  it('returns true for equal values when this.scale > value.scale', () => {
+    expect(new FixedPointNumber(500, 2).eq(new FixedPointNumber(5, 0))).toBe(true);
+  });
+
+  it('returns true for equal values when this.scale < value.scale', () => {
+    expect(new FixedPointNumber(5, 0).eq(new FixedPointNumber(500, 2))).toBe(true);
+  });
+
+  it('returns false for different values when this.scale > value.scale', () => {
+    expect(new FixedPointNumber(501, 2).eq(new FixedPointNumber(5, 0))).toBe(false);
+  });
+
+  it('returns false for different values when this.scale < value.scale', () => {
+    expect(new FixedPointNumber(5, 0).eq(new FixedPointNumber(501, 2))).toBe(false);
+  });
+
+  it('stays consistent with lt/gt for the same scale-mismatched pair', () => {
+    const a = new FixedPointNumber(500, 2);
+    const b = new FixedPointNumber(5, 0);
+    expect(a.eq(b)).toBe(true);
+    expect(a.lt(b)).toBe(false);
+    expect(a.gt(b)).toBe(false);
+  });
+
+  it('handles a larger scale delta correctly', () => {
+    expect(new FixedPointNumber(5000000, 6).eq(new FixedPointNumber(5, 0))).toBe(true);
+  });
+});