Change to bits cfg

Cargo.toml

@@ -63,11 +63,3 @@ alloc = ["zeroize/alloc"]
 fiat_backend = ["fiat-crypto"]
 # The SIMD backend uses parallel formulas, using either AVX2 or AVX512-IFMA.
 simd_backend = ["nightly", "packed_simd"]
-
-# Target backend overrides for fiat_backend
-fiat_64 = []
-fiat_32 = []
-
-# Target backend overrides for the default serial backend
-serial_64 = []
-serial_32 = []

src/backend/serial/mod.rs

@@ -22,35 +22,20 @@ use cfg_if::cfg_if;
 
 cfg_if! {
 
-    if #[cfg(any(feature = "fiat_backend", feature = "fiat_64", feature = "fiat_32"))] {
+    if #[cfg(any(feature = "fiat_backend"))] {
 
-        #[cfg(all(feature = "fiat_64", feature = "fiat_32"))]
-        compile_error!("Overrides fiat_64 or fiat_32 are mutually exclusive - cannot enable both.");
-
-        #[cfg(any(
-            all(not(target_pointer_width = "64"), not(feature = "fiat_64")),
-            feature = "fiat_32"
-        ))]
+        #[cfg(dalek_bits = "32")]
         pub mod fiat_u32;
 
-        #[cfg(any(
-            all(target_pointer_width = "64", not(feature = "fiat_32")),
-            feature = "fiat_64"
-        ))]
+        #[cfg(dalek_bits = "64")]
         pub mod fiat_u64;
 
     } else {
 
-        #[cfg(all(feature = "serial_64", feature = "serial_32"))]
-        compile_error!("Overrides serial_64 or serial_32 are mutually exclusive - cannot enable both.");
-
-        #[cfg(any(
-            all(not(target_pointer_width = "64"), not(feature = "serial_64")),
-            feature = "serial_32"
-        ))]
+        #[cfg(dalek_bits = "32")]
         pub mod u32;
 
-        #[cfg(any(all(target_pointer_width = "64", not(feature = "serial_32")), feature = "serial_64"))]
+        #[cfg(dalek_bits = "64")]
         pub mod u64;
 
     }

src/lib.rs

@@ -22,6 +22,23 @@
 )]
 #![doc(html_root_url = "https://docs.rs/curve25519-dalek/4.0.0-pre.2")]
 #![doc = include_str!("../README.md")]
+//------------------------------------------------------------------------
+// curve25519-dalek arithmetric overrides
+//------------------------------------------------------------------------
+#![cfg_attr(
+    any(
+        all(not(target_pointer_width = "64"), not(dalek_bits = "64")),
+        dalek_bits = "32"
+    ),
+    cfg(dalek_bits = "32")
+)]
+#![cfg_attr(
+    any(
+        all(target_pointer_width = "64", not(dalek_bits = "32")),
+        dalek_bits = "64"
+    ),
+    cfg(dalek_bits = "64")
+)]
 
 //------------------------------------------------------------------------
 // External dependencies: