Don't use the default hasher

src/world/mod.rs

@@ -17,6 +17,7 @@ use self::block::BlockSet;
 
 use std::sync::Arc;
 use std::collections::HashMap;
+use std::hash::{BuildHasherDefault, Hasher};
 use types::bit;
 use types::nibble;
 use protocol;
@@ -197,7 +198,7 @@ impl World {
                 section.dirty = true;
 
                 let bit_size = try!(data.read_u8());
-                let mut block_map = HashMap::new();
+                let mut block_map = HashMap::with_hasher(BuildHasherDefault::<FNVHash>::default());
                 if bit_size <= 8 {
                     let count = try!(VarInt::read_from(&mut data)).0;
                     for i in 0 .. count {
@@ -359,6 +360,27 @@ impl Chunk {
     }
 }
 
+struct FNVHash(u64);
+
+impl Hasher for FNVHash {
+    fn write(&mut self, bytes: &[u8]) {
+        for b in bytes {
+            self.0 = self.0.wrapping_mul(0x100000001b3);
+            self.0 ^= *b as u64
+        }
+    }
+
+    fn finish(&self) -> u64 {
+        self.0
+    }
+}
+
+impl Default for FNVHash {
+    fn default() -> Self {
+        FNVHash(0xcbf29ce484222325)
+    }
+}
+
 #[derive(PartialEq, Eq, Hash)]
 pub struct SectionKey {
     pos: (i32, u8, i32),
@@ -370,7 +392,7 @@ struct Section {
 
     blocks: bit::Map,
     block_map: Vec<(&'static block::Block, u32)>,
-    rev_block_map: HashMap<usize, usize>,
+    rev_block_map: HashMap<usize, usize, BuildHasherDefault<FNVHash>>,
 
     block_light: nibble::Array,
     sky_light: nibble::Array,
@@ -391,7 +413,7 @@ impl Section {
             block_map: vec![
                 (block::AIR.base(), 0xFFFFFFFF)
             ],
-            rev_block_map: HashMap::new(),
+            rev_block_map: HashMap::with_hasher(BuildHasherDefault::default()),
 
             block_light: nibble::Array::new(16 * 16 * 16),
             sky_light: nibble::Array::new(16 * 16 * 16),