Price struct integer overflow #228

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1. cuongph87

   added

   bugSomething isn't workingSomething isn't working

   on Jan 16, 2025
2. cuongph87

   closed this as completedon Mar 23, 2025
3. cuongph87

   reopened this on Dec 8, 2025
4. leocagli commented on Jun 26, 2026

   

   leocagli

   on Jun 26, 2026

   More actions

   Hi, I'd like to investigate and fix the integer overflow in the Price struct. I can add checked arithmetic and a test with boundary values. Could you assign me?
5. leocagli commented on Jun 27, 2026

   

   leocagli

   on Jun 27, 2026

   More actions

   Hi, Leo Cagliero (Open Stellar / Starmaker). I'd like to take this.

   Price { n: i32, d: i32 } overflows when comparing or cross-multiplying two prices: a.n * b.d and b.n * a.d are computed in i32, and with large numerators/denominators the product exceeds i32::MAX. The fix is to widen to i64 (or i128) for the intermediate products before comparing:

   impl Price {
       pub fn cmp_cross(&self, other: &Price) -> Ordering {
           // a.n/a.d  vs  b.n/b.d   ==>   a.n*b.d  vs  b.n*a.d   (widened)
           let lhs = i64::from(self.n) * i64::from(other.d);
           let rhs = i64::from(other.n) * i64::from(self.d);
           lhs.cmp(&rhs)
       }
   }

   i64::from(i32) * i64::from(i32) can never overflow i64, so the comparison stays exact. If there's a place that materializes the product into XDR (not just compares), I'll use checked_mul there and surface an error instead of wrapping. I'll add tests with n = i32::MAX, d = 1 against another large price to confirm no overflow and correct ordering. Could you assign me?