feat: add checked add/mul/sub #108
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cchudant
suggested changes
Jan 28, 2025
| impl CheckedMul for Felt { | ||
| fn checked_mul(&self, v: &Self) -> Option<Self> { | ||
| let res = self * v; | ||
| if res < *self { |
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I believe that implementation is wrong,
Felt::TWO * Felt::MAX will probably not work, in the same way 2u32.wrapping_mul(u32::MAX) doesn't and just returns 1.
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You are right. It should check against max(self, v)
I fixed it and added a test
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but now there is a bug for mul by zero
cchudant
suggested changes
Feb 3, 2025
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I do not believe this is a good enough check for the CheckedMul.
Here is another case:
println!("{:?}", Felt::from(u128::MAX).checked_mul(&Felt::from(u128::MAX)));This I believe overflows, but does not return None.
Checking for overflow on the multiply operation after the fact is tricky. I don't know any way to do it if we don't have the divide operation.
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What is the current behavior?
Checked operation traits are not available for Felt.
What is the new behavior?
Following traits are implemented
Does this introduce a breaking change?
No
Other information
It would make sense to impl CheckedDiv too. But the trait requires that
Divbe implemented. Something we chose to not do so far. It may be worth reconsidering this.