factor out RISCV support from the guts_api branch

TODO: figure out what environment variable should enable this

rust/guts/Cargo.toml

@@ -9,10 +9,16 @@ documentation = "https://docs.rs/blake3_guts"
 readme = "readme.md"
 edition = "2021"
 
+[dependencies]
+cfg-if = "1.0.0"
+
 [dev-dependencies]
 hex = "0.4.3"
 reference_impl = { path = "../../reference_impl" }
 
 [features]
 default = ["std"]
 std = []
+
+[build-dependencies]
+cc = "1.0.79"

rust/guts/build.rs

@@ -0,0 +1,59 @@
+use std::env;
+
+fn defined(var: &str) -> bool {
+    println!("cargo:rerun-if-env-changed={}", var);
+    env::var_os(var).is_some()
+}
+
+fn is_pure() -> bool {
+    defined("CARGO_FEATURE_PURE")
+}
+
+fn target_components() -> Vec<String> {
+    let target = env::var("TARGET").unwrap();
+    target.split("-").map(|s| s.to_string()).collect()
+}
+
+fn is_riscv64gc() -> bool {
+    target_components()[0] == "riscv64gc"
+}
+
+fn new_build() -> cc::Build {
+    let build = cc::Build::new();
+    build
+}
+
+fn build_riscv_rva23u64_assembly() {
+    println!("cargo:rustc-cfg=blake3_riscv_rva23u64_ffi");
+    let mut build = new_build();
+    let asm_path = "src/riscv_rva23u64.S";
+    build.file(asm_path);
+    build.flag("--target=riscv64");
+    build.flag("-march=rv64gcv_zbb_zvbb1p0");
+    build.flag("-menable-experimental-extensions");
+    build.compile("blake3_riscv_rva23u64_assembly");
+    println!("cargo:rerun-if-changed={asm_path}");
+}
+
+fn main() {
+    // TODO: This implementation assumes some bleeding-edge extensions, and it should probably be
+    // gated by a Cargo feature.
+    if is_riscv64gc() && !is_pure() {
+        build_riscv_rva23u64_assembly();
+    }
+
+    // The `cc` crate doesn't automatically emit rerun-if directives for the
+    // environment variables it supports, in particular for $CC. We expect to
+    // do a lot of benchmarking across different compilers, so we explicitly
+    // add the variables that we're likely to need.
+    println!("cargo:rerun-if-env-changed=CC");
+    println!("cargo:rerun-if-env-changed=CFLAGS");
+
+    // Ditto for source files, though these shouldn't change as often.
+    for file in std::fs::read_dir("../../c").unwrap() {
+        println!(
+            "cargo:rerun-if-changed={}",
+            file.unwrap().path().to_str().expect("utf-8")
+        );
+    }
+}

rust/guts/src/lib.rs

@@ -49,6 +49,8 @@ use core::ptr;
 use core::sync::atomic::{AtomicPtr, Ordering::Relaxed};
 
 pub mod portable;
+#[cfg(any(target_arch = "riscv64"))]
+pub mod riscv_rva23u64;
 
 #[cfg(test)]
 mod test;
@@ -82,8 +84,14 @@ pub const MSG_SCHEDULE: [[usize; 16]; 7] = [
     [11, 15, 5, 0, 1, 9, 8, 6, 14, 10, 2, 12, 3, 4, 7, 13],
 ];
 
-// never less than 2
-pub const MAX_SIMD_DEGREE: usize = 2;
+cfg_if::cfg_if! {
+    if #[cfg(target_arch = "riscv64")] {
+        pub const MAX_SIMD_DEGREE: usize = riscv_rva23u64::MAX_SIMD_DEGREE;
+    } else {
+        // never less than 2
+        pub const MAX_SIMD_DEGREE: usize = 2;
+    }
+}
 
 pub type CVBytes = [u8; 32];
 pub type CVWords = [u32; 8];
@@ -101,6 +109,11 @@ pub static DETECTED_IMPL: Implementation = Implementation::new(
 );
 
 fn detect() -> Implementation {
+    #[cfg(target_arch = "riscv64")]
+    {
+        return riscv_rva23u64::implementation();
+    }
+    #[allow(unreachable_code)]
     portable::implementation()
 }