diff --git a/src/lib.rs b/src/lib.rs
index 7d12d9a..e454bb2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,14 +1,144 @@
-pub fn add(left: usize, right: usize) -> usize {
-    left + right
+//! A teeworlds variable integer packer/unpacker.
+//!
+//! Packing:
+//!
+//! ```
+//! use std::io::Cursor;
+//!
+//! let mut buff = Cursor::new([0; 2]);
+//! assert!(teeint::pack(&mut buff, 64).is_ok());
+//! let buff = buff.into_inner();
+//! assert_eq!(buff[0], 0b1000_0000);
+//! assert_eq!(buff[1], 0b0000_0001);
+//! ```
+//!
+//! Or using the trait [[PackTwInt]]:
+//! ```
+//! use std::io::Cursor;
+//! use teeint::PackTwInt;
+//!
+//! let mut buff = Cursor::new([0; 2]);
+//! assert!(64.pack(&mut buff).is_ok());
+//! let buff = buff.into_inner();
+//! assert_eq!(buff[0], 0b1000_0000);
+//! assert_eq!(buff[1], 0b0000_0001);
+//! ```
+
+use std::io::{Result, Write};
+
+/// Pack a i32 into a teeworlds variable integer.
+pub fn pack(dst: &mut impl Write, mut value: i32) -> Result<()> {
+    let mut current_byte: u8 = 0;
+
+    /*
+     *  First byte: BIT_EXTEND BIT_SIGN BITS[6]
+     *  Next byte:  BIT_EXTEND BITS[7]
+     *  Last byte:  BIT_PADDING[4] BITS[4]
+     */
+
+    // If value is negative, set the sign bit and flip all the bits.
+    if value < 0 {
+        current_byte = 0b0100_0000;
+        value = !value;
+    }
+
+    // First byte: Pack the remaining 6 bits
+    current_byte |= (value & 0b0011_1111) as u8;
+    value >>= 6;
+
+    while value != 0 {
+        // We have more data, set BIT_EXTEND
+        current_byte |= 0b1000_0000;
+        dst.write(&[current_byte])?;
+        // Write the BITS[7]
+        current_byte = value as u8 & 0b0111_1111;
+        // Discard them.
+        value >>= 7;
+    }
+
+    dst.write(&[current_byte])?;
+
+    Ok(())
+}
+
+/// Trait implemented by values that can be packed to a teeworlds variable int.
+///
+/// Note that teeworlds only packs i32 values.
+///
+/// This trait is more of a convenience to allow writing `0i32.pack(&mut buff)`
+pub trait PackTwInt: Copy {
+    /// Pack this value into a teeworlds variable int.
+    fn pack(self, dst: &mut impl Write) -> Result<()>;
+}
+
+impl PackTwInt for i32 {
+    fn pack(self, dst: &mut impl Write) -> Result<()> {
+        pack(dst, self)
+    }
 }
 
 #[cfg(test)]
 mod tests {
+    use std::io::Cursor;
+
     use super::*;
 
     #[test]
-    fn it_works() {
-        let result = add(2, 2);
-        assert_eq!(result, 4);
+    pub fn pack_0() {
+        let mut buff = Cursor::new([0; 1]);
+        assert!(pack(&mut buff, 0).is_ok());
+        let buff = buff.into_inner();
+        assert_eq!(buff[0], 0b0000_0000);
+    }
+
+    #[test]
+    pub fn pack_1() {
+        let mut buff = Cursor::new([0; 1]);
+        assert!(pack(&mut buff, 1).is_ok());
+        let buff = buff.into_inner();
+        assert_eq!(buff[0], 0b0000_0001);
+    }
+
+    #[test]
+    pub fn pack_2() {
+        let mut buff = Cursor::new([0; 1]);
+        assert!(pack(&mut buff, 2).is_ok());
+        let buff = buff.into_inner();
+        assert_eq!(buff[0], 0b0000_0010);
+    }
+
+    #[test]
+    pub fn pack_minus_2() {
+        let mut buff = Cursor::new([0; 1]);
+        assert!(pack(&mut buff, -2).is_ok());
+        let buff = buff.into_inner();
+        assert_eq!(buff[0], 0b0100_0001);
+    }
+
+    #[test]
+    pub fn pack_minus_1() {
+        let mut buff = Cursor::new([0; 1]);
+        assert!(pack(&mut buff, -1).is_ok());
+        let buff = buff.into_inner();
+        assert_eq!(buff[0], 0b0100_0000);
+    }
+
+    #[test]
+    pub fn pack_0_to_63() {
+        for i in 0..64 {
+            let mut buff = Cursor::new([0; 1]);
+            assert!(pack(&mut buff, i as i32).is_ok());
+            let buff = buff.into_inner();
+            assert_eq!(buff[0], i);
+        }
+    }
+
+    #[test]
+    pub fn pack_64() {
+        let mut buff = Cursor::new([0; 2]);
+        assert!(pack(&mut buff, 64).is_ok());
+        let buff = buff.into_inner();
+        assert_eq!(buff[0], 0b1000_0000);
+        assert_eq!(buff[1], 0b0000_0001);
     }
 }