fp: refactor from_base_prime_field_elems (#965)

* fp: refactor from_base_prime_field_elems

* more refactor

Author: tcoratger

ff/src/fields/models/cubic_extension.rs

@@ -205,19 +205,14 @@ impl<P: CubicExtConfig> Field for CubicExtField<P> {
     fn from_base_prime_field_elems(
         elems: impl IntoIterator<Item = Self::BasePrimeField>,
     ) -> Option<Self> {
-        let mut elems = elems.into_iter();
-        let elems = elems.by_ref();
-        let base_ext_deg = P::BaseField::extension_degree() as usize;
-        let element = Some(Self::new(
-            P::BaseField::from_base_prime_field_elems(elems.take(base_ext_deg))?,
-            P::BaseField::from_base_prime_field_elems(elems.take(base_ext_deg))?,
-            P::BaseField::from_base_prime_field_elems(elems.take(base_ext_deg))?,
-        ));
-        if elems.next().is_some() {
-            None
-        } else {
-            element
-        }
+        let mut iter = elems.into_iter();
+        let d = P::BaseField::extension_degree() as usize;
+
+        let a = P::BaseField::from_base_prime_field_elems(iter.by_ref().take(d))?;
+        let b = P::BaseField::from_base_prime_field_elems(iter.by_ref().take(d))?;
+        let c = P::BaseField::from_base_prime_field_elems(iter.by_ref().take(d))?;
+
+        iter.next().is_none().then(|| Self::new(a, b, c))
     }
 
     #[inline]

ff/src/fields/models/fp/mod.rs

@@ -15,6 +15,7 @@ use ark_std::{
     string::*,
 };
 use core::iter;
+use itertools::Itertools;
 
 #[macro_use]
 mod montgomery_backend;
@@ -226,12 +227,7 @@ impl<P: FpConfig<N>, const N: usize> Field for Fp<P, N> {
     fn from_base_prime_field_elems(
         elems: impl IntoIterator<Item = Self::BasePrimeField>,
     ) -> Option<Self> {
-        let mut elems = elems.into_iter();
-        let elem = elems.next()?;
-        if elems.next().is_some() {
-            return None;
-        }
-        Some(elem)
+        elems.into_iter().exactly_one().ok()
     }
 
     #[inline]

ff/src/fields/models/quadratic_extension.rs

@@ -230,18 +230,13 @@ impl<P: QuadExtConfig> Field for QuadExtField<P> {
     fn from_base_prime_field_elems(
         elems: impl IntoIterator<Item = Self::BasePrimeField>,
     ) -> Option<Self> {
-        let mut elems = elems.into_iter();
-        let elems = elems.by_ref();
-        let base_ext_deg = P::BaseField::extension_degree() as usize;
-        let element = Some(Self::new(
-            P::BaseField::from_base_prime_field_elems(elems.take(base_ext_deg))?,
-            P::BaseField::from_base_prime_field_elems(elems.take(base_ext_deg))?,
-        ));
-        if elems.next().is_some() {
-            None
-        } else {
-            element
-        }
+        let mut iter = elems.into_iter();
+        let d = P::BaseField::extension_degree() as usize;
+
+        let a = P::BaseField::from_base_prime_field_elems(iter.by_ref().take(d))?;
+        let b = P::BaseField::from_base_prime_field_elems(iter.by_ref().take(d))?;
+
+        iter.next().is_none().then(|| Self::new(a, b))
     }
 
     fn square(&self) -> Self {