define for relevant simd

build.rs

@@ -13,13 +13,34 @@ fn main() {
         std::process::exit(1)
     }
 
+    let wrapper_defs_dir = &env::var_os("OUT_DIR").unwrap();
+    let wrapper_defs_dir = Path::new(&wrapper_defs_dir);
+    let dest_path = wrapper_defs_dir.join("wrapper_defs.h");
+    use std::env;
+    use std::path::Path;
+    let target_env = std::env::var("TARGET");
+    let define_value = match target_env {
+        // srsly. There must be a better way.
+        Ok(s) if s == "x86_64-unknown-linux-gnu" => "#define RAPIDJSON_SSE42".into(),
+        Ok(s) if s == "x86_64-pc-windows-gnu" => "#define RAPIDJSON_SSE42".into(),
+        Ok(s) if s == "arm64e-apple-darwin"=> "#define RAPIDJSON_NEON".into(),
+        wut => format!("// whaddya mean {:?}", wut),
+    };
+    if option_env!("RAPIDJSON_SSE42").is_some() {
+        std::fs::write(&dest_path, define_value).unwrap();
+    } else {
+        std::fs::write(&dest_path, "").unwrap();
+    }
+
     cxx_build::bridge("src/rapid.rs")
         .include(rapidjson_include)
+        .include(wrapper_defs_dir)
         .file("src/wrapper.cc")
         .cpp(true)
         .std("c++20")
         .compile("rapid");
 
+    println!("cargo::rerun-if-changed=build.rs");
     println!("cargo::rerun-if-changed=src/rapid.rs");
     println!("cargo::rerun-if-changed=src/wrapper.cc");
     println!("cargo::rerun-if-changed=src/wrapper.h");

src/wrapper.cc

@@ -5,10 +5,10 @@
 // NOTE jch is just what cxx-build wants to call it, because of the cargo package name.
 #include "jch/src/rapid.rs.h"
 
-// turn on simd instructions
-// #define RAPIDJSON_SSE42
+// Turn on simd instructions for the architecture.
+// The file is generated by build.rs
+#include "wrapper_defs.h"
 
-// TODO vendor or git-submodule this into the build tree
 #include "rapidjson/fwd.h"
 #include "rapidjson/rapidjson.h"
 #include "rapidjson/reader.h"