const new for SendPropIdentifier

src/consthash.rs

@@ -0,0 +1,46 @@
+pub struct ConstFnvHash(u64);
+
+impl ConstFnvHash {
+    pub const fn new() -> Self {
+        Self(0xcbf29ce484222325)
+    }
+
+    pub const fn push_string(self, str: &str) -> Self {
+        self.update(str.as_bytes()).update(&[0xff])
+    }
+
+    pub const fn update(self, bytes: &[u8]) -> Self {
+        let Self(mut hash) = self;
+
+        let mut i = 0;
+        while i < bytes.len() {
+            let byte = bytes[i];
+            hash = hash ^ (byte as u64);
+            hash = hash.wrapping_mul(0x100000001b3);
+            i += 1;
+        }
+
+        Self(hash)
+    }
+
+    pub const fn finish(self) -> u64 {
+        self.0
+    }
+}
+
+#[test]
+fn test_const_fnv() {
+    use fnv::FnvHasher;
+    use std::hash::Hash;
+    use std::hash::Hasher;
+
+    let mut hasher = FnvHasher::default();
+    "foobar".hash(&mut hasher);
+    "another input".hash(&mut hasher);
+    let hash = hasher.finish();
+
+    let hasher = ConstFnvHash::new();
+    let hasher = hasher.push_string("foobar");
+    let hasher = hasher.push_string("another input");
+    assert_eq!(hasher.finish(), hash);
+}