A small script outlining binary encoding int64 and uint64. (https://play.golang.org/p/t_xT3PcpcK)

encoding_int64.go

package main

import (
	"fmt"
	"encoding/binary"
)

func main() {
	//
	// Largest signed int64 in smallest byte slice.
	//

	var signedInt64 int64 = 9223372036854775807
	
	a := make([]byte, 10)
	binary.PutVarint(a, signedInt64)
	
	decodedSignedInt64, _ := binary.Varint(a)
	
	fmt.Println(a, decodedSignedInt64)

	//
	// Largest unsigned int64 in smallest byte slice.
	//

	var unsignedInt64 uint64 = 18446744073709551615
	
	b := make([]byte, 10)
	binary.PutUvarint(b, unsignedInt64)
	
	decodedUnsignedInt64, _ := binary.Uvarint(b)
	
	fmt.Println(b, decodedUnsignedInt64)
}

// Output:
// [254 255 255 255 255 255 255 255 255 1] 9223372036854775807
// [255 255 255 255 255 255 255 255 255 1] 18446744073709551615