cpu: Have "rdrand" feature take precedence over "custom"

.travis.yml

@@ -145,11 +145,11 @@ jobs:
       script:
         # We test that getrandom builds for all targets
         - echo $STD_TARGETS | xargs -t -n1 cargo build --target
-        - echo $NO_STD_TARGETS | xargs -t -n1 cargo xbuild --features=cpu --target
+        - echo $NO_STD_TARGETS | xargs -t -n1 cargo xbuild --features=rdrand --target
         # also test minimum dependency versions are usable
         - cargo generate-lockfile -Z minimal-versions
         - echo $STD_TARGETS | xargs -t -n1 cargo build --target
-        - echo $NO_STD_TARGETS | xargs -t -n1 cargo xbuild --features=cpu --target
+        - echo $NO_STD_TARGETS | xargs -t -n1 cargo xbuild --features=rdrand --target
 
     # Trust cross-built/emulated targets. We must repeat all non-default values.
     - name: "Linux (MIPS, big-endian)"

Cargo.toml

@@ -35,8 +35,8 @@ wasi = "0.9"
 
 [features]
 std = []
-# Feature to enable fallback CPU-based implementation
-cpu = []
+# Feature to enable fallback RDRAND-based implementation
+rdrand = []
 # Feature to enable custom RNG implementations
 custom = []
 # Unstable feature to support being a libstd dependency

src/lib.rs

@@ -183,11 +183,11 @@ cfg_if! {
         #[path = "windows.rs"] mod imp;
     } else if #[cfg(all(target_arch = "x86_64", target_env = "sgx"))] {
         #[path = "rdrand.rs"] mod imp;
-    } else if #[cfg(feature = "custom")] {
-        use custom as imp;
-    } else if #[cfg(all(feature = "cpu",
+    } else if #[cfg(all(feature = "rdrand",
                         any(target_arch = "x86_64", target_arch = "x86")))] {
         #[path = "rdrand.rs"] mod imp;
+    } else if #[cfg(feature = "custom")] {
+        use custom as imp;
     } else {
         compile_error!("\
             target is not supported, for more information see: \
@@ -219,4 +219,4 @@ pub fn getrandom(dest: &mut [u8]) -> Result<(), Error> {
 #[cfg(test)]
 mod test_common;
 #[cfg(test)]
-mod test_cpu;
+mod test_rdrand;

src/test_cpu.rs → src/test_rdrand.rs

@@ -1,4 +1,4 @@
-// We only test the CPU-based RNG source on supported architectures.
+// We only test the RDRAND-based RNG source on supported architectures.
 #![cfg(any(target_arch = "x86_64", target_arch = "x86"))]
 
 #[path = "rdrand.rs"]