Initial cuda support

cuda/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "plonky2-cuda"
+version = "0.1.0"
+authors = ["Mozak"]
+description = "GPU acceleration for plonky2"
+edition = "2021"
+
+[build-dependencies.cc]
+version = "^1.0.70"
+
+[build-dependencies.which]
+version = "^4.0"
+

cuda/build.rs

@@ -0,0 +1,26 @@
+use std::{env};
+
+fn main() {
+
+    // Detect if there is CUDA compiler and engage "cuda" feature accordingly
+    let nvcc = match env::var("NVCC") {
+        Ok(var) => which::which(var),
+        Err(_) => which::which("nvcc"),
+    };
+
+    if nvcc.is_ok() {
+        let mut nvcc = cc::Build::new();
+        nvcc.cuda(true);
+        nvcc.flag("-g");
+        nvcc.flag("-O5");
+        nvcc.flag("-arch=sm_75");
+        nvcc.flag("-maxrregcount=255");
+        nvcc.file("plonky2_gpu.cu").compile("plonky2_cuda");
+
+        println!("cargo:rustc-cfg=feature=\"cuda\"");
+        println!("cargo:rerun-if-changed=cuda");
+        println!("cargo:rerun-if-env-changed=CXXFLAGS");
+    } else {
+        println!("nvcc must be in the path. Consider adding /usr/local/cuda/bin.");
+    }
+}