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sub_nonnative fix

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This commit is contained in:
Nicholas Ward 2021-11-09 17:21:16 -08:00
parent 656f052b79
commit db31b9f662
1 changed files with 7 additions and 4 deletions
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11
src/gadgets/nonnative.rs
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@ -51,16 +51,19 @@ impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilder<F, D> {
self.reduce(&result)
}
// Subtract two `ForeignFieldTarget`s. We assume that the first is larger than the second.
// Subtract two `ForeignFieldTarget`s.
pub fn sub_nonnative<FF: Field>(
&mut self,
a: &ForeignFieldTarget<FF>,
b: &ForeignFieldTarget<FF>,
) -> ForeignFieldTarget<FF> {
let a_biguint = self.ff_to_biguint(a);
let b_biguint = self.ff_to_biguint(b);
let result = self.sub_biguint(&a_biguint, &b_biguint);
let order = self.constant_biguint(&FF::order());
let a_biguint = self.nonnative_to_biguint(a);
let a_plus_order = self.add_biguint(&order, &a_biguint);
let b_biguint = self.nonnative_to_biguint(b);
let result = self.sub_biguint(&a_plus_order, &b_biguint);
// TODO: reduce sub result with only one conditional addition?
self.reduce(&result)
}