Enable RISC-V build

Cargo.toml

@@ -12,8 +12,10 @@ categories = ["cryptography::cryptocurrencies"]
 
 [dependencies]
 lazy_static = { version = "1.1", optional = true }
-cpufeatures = { version = "0.2", optional = true }
 ring = "0.17"
+
+[target.'cfg(target_arch = "x86_64")'.dependencies]
+cpufeatures = "0.2"
 sha2 = "0.10"
 
 [dev-dependencies]
@@ -23,6 +25,5 @@ rustc-hex = "2"
 wasm-bindgen-test = "0.3.33"
 
 [features]
-default = ["zero_hash_cache", "detect-cpufeatures"]
+default = ["zero_hash_cache"]
 zero_hash_cache = ["lazy_static"]
-detect-cpufeatures = ["cpufeatures"]

src/lib.rs

@@ -7,8 +7,12 @@
 //! Now this crate serves primarily as a wrapper over two SHA256 crates: `sha2` and `ring` – which
 //! it switches between at runtime based on the availability of SHA intrinsics.
 
+mod sha2_impl;
+
 pub use self::DynamicContext as Context;
-use sha2::Digest;
+
+#[cfg(target_arch = "x86_64")]
+use sha2_impl::Sha2CrateImpl;
 
 #[cfg(feature = "zero_hash_cache")]
 use lazy_static::lazy_static;
@@ -54,35 +58,6 @@ pub trait Sha256 {
     fn hash_fixed(&self, input: &[u8]) -> [u8; HASH_LEN];
 }
 
-/// Implementation of SHA256 using the `sha2` crate (fastest on CPUs with SHA extensions).
-struct Sha2CrateImpl;
-
-impl Sha256Context for sha2::Sha256 {
-    fn new() -> Self {
-        sha2::Digest::new()
-    }
-
-    fn update(&mut self, bytes: &[u8]) {
-        sha2::Digest::update(self, bytes)
-    }
-
-    fn finalize(self) -> [u8; HASH_LEN] {
-        sha2::Digest::finalize(self).into()
-    }
-}
-
-impl Sha256 for Sha2CrateImpl {
-    type Context = sha2::Sha256;
-
-    fn hash(&self, input: &[u8]) -> Vec<u8> {
-        Self::Context::digest(input).into_iter().collect()
-    }
-
-    fn hash_fixed(&self, input: &[u8]) -> [u8; HASH_LEN] {
-        Self::Context::digest(input).into()
-    }
-}
-
 /// Implementation of SHA256 using the `ring` crate (fastest on CPUs without SHA extensions).
 pub struct RingImpl;
 
@@ -120,34 +95,39 @@ impl Sha256 for RingImpl {
 
 /// Default dynamic implementation that switches between available implementations.
 pub enum DynamicImpl {
+    #[cfg(target_arch = "x86_64")]
     Sha2,
     Ring,
 }
 
 // Runtime latch for detecting the availability of SHA extensions on x86_64.
 //
 // Inspired by the runtime switch within the `sha2` crate itself.
-#[cfg(all(feature = "detect-cpufeatures", target_arch = "x86_64"))]
+#[cfg(target_arch = "x86_64")]
 cpufeatures::new!(x86_sha_extensions, "sha", "sse2", "ssse3", "sse4.1");
 
 #[inline(always)]
 pub fn have_sha_extensions() -> bool {
-    #[cfg(all(feature = "detect-cpufeatures", target_arch = "x86_64"))]
+    #[cfg(target_arch = "x86_64")]
     return x86_sha_extensions::get();
 
-    #[cfg(not(all(feature = "detect-cpufeatures", target_arch = "x86_64")))]
+    #[cfg(not(target_arch = "x86_64"))]
     return false;
 }
 
 impl DynamicImpl {
     /// Choose the best available implementation based on the currently executing CPU.
     #[inline(always)]
     pub fn best() -> Self {
+        #[cfg(target_arch = "x86_64")]
         if have_sha_extensions() {
             Self::Sha2
         } else {
             Self::Ring
         }
+
+        #[cfg(not(target_arch = "x86_64"))]
+        Self::Ring
     }
 }
 
@@ -157,6 +137,7 @@ impl Sha256 for DynamicImpl {
     #[inline(always)]
     fn hash(&self, input: &[u8]) -> Vec<u8> {
         match self {
+            #[cfg(target_arch = "x86_64")]
             Self::Sha2 => Sha2CrateImpl.hash(input),
             Self::Ring => RingImpl.hash(input),
         }
@@ -165,6 +146,7 @@ impl Sha256 for DynamicImpl {
     #[inline(always)]
     fn hash_fixed(&self, input: &[u8]) -> [u8; HASH_LEN] {
         match self {
+            #[cfg(target_arch = "x86_64")]
             Self::Sha2 => Sha2CrateImpl.hash_fixed(input),
             Self::Ring => RingImpl.hash_fixed(input),
         }
@@ -175,27 +157,31 @@ impl Sha256 for DynamicImpl {
 ///
 /// This enum ends up being 8 bytes larger than the largest inner context.
 pub enum DynamicContext {
+    #[cfg(target_arch = "x86_64")]
     Sha2(sha2::Sha256),
     Ring(ring::digest::Context),
 }
 
 impl Sha256Context for DynamicContext {
     fn new() -> Self {
         match DynamicImpl::best() {
+            #[cfg(target_arch = "x86_64")]
             DynamicImpl::Sha2 => Self::Sha2(Sha256Context::new()),
             DynamicImpl::Ring => Self::Ring(Sha256Context::new()),
         }
     }
 
     fn update(&mut self, bytes: &[u8]) {
         match self {
+            #[cfg(target_arch = "x86_64")]
             Self::Sha2(ctxt) => Sha256Context::update(ctxt, bytes),
             Self::Ring(ctxt) => Sha256Context::update(ctxt, bytes),
         }
     }
 
     fn finalize(self) -> [u8; HASH_LEN] {
         match self {
+            #[cfg(target_arch = "x86_64")]
             Self::Sha2(ctxt) => Sha256Context::finalize(ctxt),
             Self::Ring(ctxt) => Sha256Context::finalize(ctxt),
         }

src/sha2_impl.rs

@@ -0,0 +1,35 @@
+// This implementation should only be compiled on x86_64 due to its dependency on the `sha2` and
+// `cpufeatures` crates which do not compile on some architectures like RISC-V.
+#![cfg(target_arch = "x86_64")]
+
+use crate::{Sha256, Sha256Context, HASH_LEN};
+use sha2::Digest;
+
+/// Implementation of SHA256 using the `sha2` crate (fastest on x86_64 CPUs with SHA extensions).
+pub struct Sha2CrateImpl;
+
+impl Sha256Context for sha2::Sha256 {
+    fn new() -> Self {
+        sha2::Digest::new()
+    }
+
+    fn update(&mut self, bytes: &[u8]) {
+        sha2::Digest::update(self, bytes)
+    }
+
+    fn finalize(self) -> [u8; HASH_LEN] {
+        sha2::Digest::finalize(self).into()
+    }
+}
+
+impl Sha256 for Sha2CrateImpl {
+    type Context = sha2::Sha256;
+
+    fn hash(&self, input: &[u8]) -> Vec<u8> {
+        Self::Context::digest(input).into_iter().collect()
+    }
+
+    fn hash_fixed(&self, input: &[u8]) -> [u8; HASH_LEN] {
+        Self::Context::digest(input).into()
+    }
+}