Stupid hash function made on a plane without WiFi

main.go

// go build
// ./main "random string"
// 2f4563a971944e00

package main

import (
	"fmt"
	"os"
)

func main() {
	fmt.Println(hexprint(hash([]byte(os.Args[1]))))
}

func hexprint(a uint64) string {
	return fmt.Sprintf("%016x", a)
}

func hash(input []byte) uint64 {
	pad := Padding(input, 64)
	msgblocks := Split(pad, 8)

	nums := make([]uint64, 0)
	for _, blk := range msgblocks {
		num := uint64(0)

		multip := uint64(1)
		for _, b := range blk {
			num += uint64(b) * multip
			multip *= 1 << 8
		}
		nums = append(nums, num)
	}

	result := uint64(0)
	for i := uint64(0); i < 63; i++ {
		for _, num := range nums {
			result ^= Rotr(num, i) * Rotr(num, i) * num * num * 0x428a2f98 // overflow is essentially mod 2^64
		}
	}
	return result
}

func Padding(input []byte, length int) []byte {
	mod := len(input) % length
	padcount := length - mod
	if mod > length-8 {
		padcount += 64
	}

	for i := 0; i < padcount; i++ {
		input = append(input, 0x0)
	}

	return input
}

func Split(input []byte, length int) [][]byte {
	var barr [][]byte
	n := len(input) / length
	for i := 0; i < n; i++ {
		barr = append(barr, input[i*length:(i+1)*length])
	}
	return barr
}

func Rotr(x, n uint64) uint64 {
	return x<<(64-n) | x>>n
}