diff --git a/bytes/bytes_test.mbt b/bytes/bytes_test.mbt
index 657a6c11..88fec3c9 100644
--- a/bytes/bytes_test.mbt
+++ b/bytes/bytes_test.mbt
@@ -24,8 +24,12 @@ test "hash" {
   let b2 = Bytes::[
     65, 0, 66, 0, 67, 0, 68, 0, 69, 0, 70, 0, 71, 0, 72, 0, 74, 0,
   ]
+  let b3 = Bytes::[128, 0, 0, 0, 0, 0, 0, 0]
+  let b4 = Bytes::[127, 255, 255, 255, 255, 255, 255, 255]
   inspect(b1.hash(), content="273427599")?
   inspect(b2.hash(), content="2013728637")?
+  inspect(b3.hash(), content="-983520567")?
+  inspect(b4.hash(), content="-1652773543")?
   inspect(b1.hash() == b1.hash(), content="true")?
   inspect(b2.hash() == b2.hash(), content="true")?
   inspect(b1.hash() == b2.hash(), content="false")?
diff --git a/bytes/xxhash.mbt b/bytes/xxhash.mbt
index d6713416..016eb1cf 100644
--- a/bytes/xxhash.mbt
+++ b/bytes/xxhash.mbt
@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// https://github.com/Cyan4973/xxHash/blob/dev/doc/xxhash_spec.md#xxh32-algorithm-description
+
 let gPRIME1 = -1640531535
 
 let gPRIME2 = -2048144777
diff --git a/int64/int64.mbt b/int64/int64.mbt
index c0def2e3..859e8ef1 100644
--- a/int64/int64.mbt
+++ b/int64/int64.mbt
@@ -47,25 +47,3 @@ pub fn Int64::max_value() -> Int64 {
 pub fn Int64::min_value() -> Int64 {
   min_val
 }
-
-pub fn hash(self : Int64) -> Int {
-  let b = Bytes::make(8)
-  b[0] = self.lsr(56).to_byte()
-  b[1] = self.lsr(48).land(0xFFL).to_byte()
-  b[2] = self.lsr(40).land(0xFFL).to_byte()
-  b[3] = self.lsr(32).land(0xFFL).to_byte()
-  b[4] = self.lsr(24).land(0xFFL).to_byte()
-  b[5] = self.lsr(16).land(0xFFL).to_byte()
-  b[6] = self.lsr(8).land(0xFFL).to_byte()
-  b[7] = self.land(0xFFL).to_byte()
-  b.hash()
-}
-
-test "int64 hash" {
-  @assertion.assert_eq(0L.hash(), 0L.hash())?
-  @assertion.assert_eq(1L.hash(), 1L.hash())?
-  @assertion.assert_ne(0L.hash(), 1L.hash())?
-  @assertion.assert_eq(0x7fffffffffffffffL.hash(), 0x7fffffffffffffffL.hash())?
-  @assertion.assert_ne(0x7fffffffffffffffL.hash(), 0x8000000000000000L.hash())?
-  @assertion.assert_eq(0x8000000000000000L.hash(), 0x8000000000000000L.hash())?
-}
diff --git a/int64/xxhash.mbt b/int64/xxhash.mbt
new file mode 100644
index 00000000..85b0a29e
--- /dev/null
+++ b/int64/xxhash.mbt
@@ -0,0 +1,76 @@
+// Copyright 2024 International Digital Economy Academy
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+pub fn slow_hash(self : Int64) -> Int {
+  let b = Bytes::make(8)
+  b[7] = self.lsr(56).to_byte()
+  b[6] = self.lsr(48).land(0xFFL).to_byte()
+  b[5] = self.lsr(40).land(0xFFL).to_byte()
+  b[4] = self.lsr(32).land(0xFFL).to_byte()
+  b[3] = self.lsr(24).land(0xFFL).to_byte()
+  b[2] = self.lsr(16).land(0xFFL).to_byte()
+  b[1] = self.lsr(8).land(0xFFL).to_byte()
+  b[0] = self.land(0xFFL).to_byte()
+  b.hash()
+}
+
+// Not needed for 8 bytes data
+// let gPRIME1 = -1640531535
+
+let gPRIME2 = -2048144777
+
+let gPRIME3 = -1028477379
+
+let gPRIME4 = 668265263
+
+let gPRIME5 = 374761393
+
+// https://github.com/Cyan4973/xxHash/blob/dev/doc/xxhash_spec.md#xxh32-algorithm-description
+// For a more readable version, see bytes/xxhash.mbt
+pub fn hash(self : Int64) -> Int {
+  let mut input = self
+  let seed = 0
+  let mut len = 8
+  let mut acc = seed + gPRIME5 + len
+  while len > 0 {
+    len -= 4
+    let x = acc + input.to_int() * gPRIME3
+    let r = 17
+    acc = x.lsl(r).lor(x.lsr(32 - r)) * gPRIME4
+    input = input.lsr(32)
+  }
+  acc = acc.lxor(acc.lsr(15))
+  acc *= gPRIME2
+  acc = acc.lxor(acc.lsr(13))
+  acc *= gPRIME3
+  acc = acc.lxor(acc.lsr(16))
+  acc
+}
+
+test "hash" {
+  let i0 = 9_223_372_036_854_775_807L // INT64_MAX
+  let i1 = -9_223_372_036_854_775_808L // INT64_MIN
+  let i2 = gPRIME2.to_int64()
+  let i3 = gPRIME3.to_int64()
+  let i4 = gPRIME4.to_int64()
+  let i5 = gPRIME5.to_int64()
+  let i6 = 0L
+  inspect(i0.hash().to_string(), content=i0.slow_hash().to_string())?
+  inspect(i1.hash().to_string(), content=i1.slow_hash().to_string())?
+  inspect(i2.hash().to_string(), content=i2.slow_hash().to_string())?
+  inspect(i3.hash().to_string(), content=i3.slow_hash().to_string())?
+  inspect(i4.hash().to_string(), content=i4.slow_hash().to_string())?
+  inspect(i5.hash().to_string(), content=i5.slow_hash().to_string())?
+  inspect(i6.hash().to_string(), content=i6.slow_hash().to_string())?
+}