k256: remove field-montgomery feature (#404)

Removes the original legacy field implementation inherited (in modified
form) from the `p256` crate.

At this point the new field implementations seem fairly solid, so
there's little reason to keep it around besides additional complexity.

Author: tarcieri

.github/workflows/k256.yml

@@ -96,7 +96,6 @@ jobs:
       - run: cargo check --target ${{ matrix.target }} --all-features
       - run: cargo test --release --target ${{ matrix.target }} --no-default-features
       - run: cargo test --release --target ${{ matrix.target }}
-      - run: cargo test --release --target ${{ matrix.target }} --features field-montgomery
       - run: cargo test --release --target ${{ matrix.target }} --all-features
 
 # TODO(tarcieri): re-enable when new `elliptic-curve` and `ecdsa` crates are released

k256/Cargo.toml

@@ -44,7 +44,6 @@ digest = ["ecdsa-core/digest", "ecdsa-core/hazmat"]
 ecdh = ["arithmetic", "elliptic-curve/ecdh", "zeroize"]
 ecdsa = ["arithmetic", "digest", "ecdsa-core/sign", "ecdsa-core/verify", "zeroize"]
 expose-field = ["arithmetic"]
-field-montgomery = []
 jwk = ["elliptic-curve/jwk"]
 keccak256 = ["digest", "sha3"]
 pem = ["elliptic-curve/pem", "pkcs8"]

k256/src/arithmetic/field.rs

@@ -3,9 +3,7 @@
 use cfg_if::cfg_if;
 
 cfg_if! {
-    if #[cfg(feature = "field-montgomery")] {
-        mod field_montgomery;
-    } else if #[cfg(target_pointer_width = "32")] {
+    if #[cfg(target_pointer_width = "32")] {
         mod field_10x26;
     } else if #[cfg(target_pointer_width = "64")] {
         mod field_5x52;
@@ -15,14 +13,12 @@ cfg_if! {
 }
 
 cfg_if! {
-    if #[cfg(all(debug_assertions, not(feature = "field-montgomery")))] {
+    if #[cfg(debug_assertions)] {
         mod field_impl;
         use field_impl::FieldElementImpl;
     } else {
         cfg_if! {
-            if #[cfg(feature = "field-montgomery")] {
-                use field_montgomery::FieldElementMontgomery as FieldElementImpl;
-            } else if #[cfg(target_pointer_width = "32")] {
+            if #[cfg(target_pointer_width = "32")] {
                 use field_10x26::FieldElement10x26 as FieldElementImpl;
             } else if #[cfg(target_pointer_width = "64")] {
                 use field_5x52::FieldElement5x52 as FieldElementImpl;