package main

import (
	`fmt`
	`log`
	"strconv"
)

const (
	/*
		This is a nonsensical example.
		The actual values are sort of scattered around a multitude of RFCs.
	*/
	deBits string = "01010101" // [0101 0101], or 85 (0x55)
)

var (
	deLowerMask uint8 = 0x03 // 3
)

func ToDE(dscp, ecn uint8) (de byte) {

	de = (dscp << 2) | (ecn & deLowerMask)

	return
}

func FromDE(de byte) (dscp, ecn uint8) {

	dscp = de >> 2
	ecn = de & deLowerMask

	return
}

func main() {

	var err error
	var u64 uint64
	var de byte
	var dscp uint8
	var ecn uint8

	// Given a D/E of deBits (see const at top)...
	if u64, err = strconv.ParseUint(deBits, 2, 8); err != nil {
		log.Panicln(err)
	}
	de = uint8(u64)
	// Prints:
	/*
		D/E is:		85 (0x55)
	*/
	fmt.Printf("D/E is:\t\t%d (%#02x)\n", de, de)

	dscp, ecn = FromDE(de)
	// Prints:
	/*
		DSCP:		21 (0x15)
		ECN:		1 (0x01)
	*/
	fmt.Printf(
		"DSCP:\t\t%d (%#02x)\n"+
			"ECN:\t\t%d (%#02x)\n",
		dscp, dscp,
		ecn, ecn,
	)

	de = ToDE(dscp, ecn)
	// Prints:
	/*
		Confirmed D/E:	85 (0x55)
	*/
	fmt.Printf("Confirmed D/E:\t%d (%#02x)\n", de, de)
}