Use bytemuck instead of unsafe Rust

Cargo.lock

@@ -23,6 +23,12 @@ version = "2.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6dbe3c979c178231552ecba20214a8272df4e09f232a87aef4320cf06539aded"
 
+[[package]]
+name = "bytemuck"
+version = "1.13.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "17febce684fd15d89027105661fec94afb475cb995fbc59d2865198446ba2eea"
+
 [[package]]
 name = "bytes"
 version = "1.4.0"
@@ -58,6 +64,7 @@ dependencies = [
 name = "gbt"
 version = "0.1.0"
 dependencies = [
+ "bytemuck",
  "bytes",
  "napi",
  "napi-build",

backend/rust-gbt/Cargo.toml

@@ -17,6 +17,7 @@ bytes = "1.4.0"
 once_cell = "1.18.0"
 napi = { version = "2.13.2", features = ["napi8", "tokio_rt"] }
 napi-derive = "2.13.0"
+bytemuck = "1.13.1"
 
 [build-dependencies]
 napi-build = "2.0.1"

backend/rust-gbt/src/u32_hashmap.rs

@@ -31,16 +31,16 @@ pub struct U32Hasher(u32);
 impl Hasher for U32Hasher {
     fn finish(&self) -> u64 {
         // Safety: Two u32s next to each other will make a u64
-        unsafe { core::mem::transmute::<(u32, u32), u64>((self.0, 0_u32)) }
+        bytemuck::cast([self.0, 0])
     }
 
     fn write(&mut self, bytes: &[u8]) {
         // Assert in debug builds (testing too) that only 4 byte keys (u32, i32, f32, etc.) run
         debug_assert!(bytes.len() == 4);
-        // Safety: We know that the size of the key is at least 4 bytes
+        // Safety: We know that the size of the key is 4 bytes
         // We also know that the only way to get an instance of HashMap using this "hasher"
-        // is through the public functions in this module which set the key to u32.
-        self.0 = unsafe { *bytes.as_ptr().cast::<u32>() };
+        // is through the public functions in this module which set the key type to u32.
+        self.0 = *bytemuck::from_bytes(bytes);
     }
 }