fixing negations for fiat and gt impl

curve25519-elligator2/src/backend/serial/fiat_u64/field.rs

@@ -263,9 +263,6 @@ impl FieldElement51 {
     /// Returns 1 if self is greater than the other and 0 otherwise
     // implementation based on C libgmp -> mpn_sub_n
     pub(crate) fn gt(&self, other: &Self) -> Choice {
-        let mut result_loose = fiat_25519_loose_field_element([0; 5]);
-        fiat_25519_sub(&mut result_loose, &self.0, &rhs.0);
-
         let mut _ul = 0_u64;
         let mut _vl = 0_u64;
         let mut _rl = 0_u64;

curve25519-elligator2/src/elligator2.rs

@@ -129,6 +129,8 @@ use crate::field::FieldElement;
 use crate::montgomery::MontgomeryPoint;
 use crate::EdwardsPoint;
 
+use core::ops::Neg;
+
 use cfg_if::cfg_if;
 use subtle::{
     Choice, ConditionallyNegatable, ConditionallySelectable, ConstantTimeEq, ConstantTimeGreater,
@@ -504,8 +506,7 @@ pub(crate) fn point_to_representative(
 
     // a := point
     let a = &FieldElement::from_bytes(&point.0);
-    let mut a_neg = *a;
-    a_neg.negate();
+    let a_neg = -&*a;
 
     let is_encodable = is_encodable(a);
 
@@ -541,7 +542,7 @@ fn is_encodable(u: &FieldElement) -> Choice {
 
     let b2 = &(&b0.square().square().square() * &b0.square().square()) * &b0.square(); // (u + A)^14
     let mut chi = &(&c.square().square() * &u.square()) * &b2; // chi = -c^4 * u^2 * (u + A)^14
-    chi.negate();
+    chi = -χ
 
     let chi_bytes = chi.as_bytes();
 
@@ -630,8 +631,7 @@ fn map_to_curve_parts(
 ) -> (FieldElement, FieldElement, FieldElement, FieldElement) {
     let zero = FieldElement::ZERO;
     let one = FieldElement::ONE;
-    let mut minus_one = FieldElement::ONE;
-    minus_one.negate();
+    let minus_one = -&FieldElement::ONE;
 
     // Exceptional case 2u^2 == -1
     let mut tv1 = r.square2();