make 32-bit backend the default

.github/workflows/rust.yml

@@ -22,11 +22,11 @@ jobs:
     name: Test Suite
     runs-on: buildjet-16vcpu-ubuntu-2204
     # We want to run the tests twice, once with the
-    # default backend (u64) and one with the u32_backend,
+    # default backend (u32) and one with the u64_backend,
     # in both cases with the r1cs feature enabled.
     strategy:
       matrix:
-        backend: ["r1cs", "r1cs,u32_backend"]
+        backend: ["r1cs", "r1cs,u64_backend"]
     steps:
       - uses: actions/checkout@v4
       - name: Install rust toolchain

Cargo.toml

@@ -68,7 +68,7 @@ arkworks = [
     "hashbrown",
 ]
 r1cs = ["arkworks", "ark-groth16", "ark-r1cs-std", "ark-relations", "ark-snark"]
-u32_backend = []
+u64_backend = ["arkworks"]
 
 [dev-dependencies]
 proptest = "1"

README.md

@@ -30,7 +30,7 @@ website](https://protocol.penumbra.zone/main/crypto/decaf377.html).
 * `std`: default, for use in `std` environments,
 * `alloc`: default, for use in `alloc` environments,
 * `arkworks`: default, uses Arkworks crates for elliptic curve operations,
-* `u32_backend`: uses 32-bit finite field arithmetic (default is 64-bit),
+* `u64_backend`: uses 64-bit finite field arithmetic (default is 32-bit),
 * `r1cs`: enables rank-1 constraint system gadgets,
 * `parallel`: enables the use of parallelism.
 

src/fields/fp.rs

@@ -8,14 +8,14 @@ pub mod arkworks;
 mod ops;
 mod u32;
 
-#[cfg(not(feature = "u32_backend"))]
+#[cfg(feature = "u64_backend")]
 mod u64;
 
 cfg_if! {
-    if #[cfg(feature = "u32_backend")] {
-        pub type Fp = u32::Fp;
-    } else {
+    if #[cfg(feature = "u64_backend")] {
         pub type Fp = u64::Fp;
+    } else {
+        pub type Fp = u32::Fp;
     }
 }
 

src/fields/fq.rs

@@ -8,14 +8,14 @@ pub mod arkworks;
 mod ops;
 mod u32;
 
-#[cfg(not(feature = "u32_backend"))]
+#[cfg(feature = "u64_backend")]
 mod u64;
 
 cfg_if! {
-    if #[cfg(feature = "u32_backend")] {
-        pub type Fq = u32::Fq;
-    } else {
+    if #[cfg(feature = "u64_backend")] {
         pub type Fq = u64::Fq;
+    } else {
+        pub type Fq = u32::Fq;
     }
 }
 

src/fields/fr.rs

@@ -8,14 +8,14 @@ pub mod arkworks;
 mod ops;
 pub mod u32;
 
-#[cfg(not(feature = "u32_backend"))]
+#[cfg(feature = "u64_backend")]
 pub mod u64;
 
 cfg_if! {
-    if #[cfg(feature = "u32_backend")] {
-        pub type Fr = u32::Fr;
-    } else {
+    if #[cfg(feature = "u64_backend")] {
         pub type Fr = u64::Fr;
+    } else {
+        pub type Fr = u32::Fr;
     }
 }