const fs = require('fs')
const file = 'file.bin'
const crypto = require('crypto')
const assert = require('assert')

let start = 10
let length = 20

let data = fs.readFileSync(file)
let md5sum = crypto.createHash('md5')
md5sum.update(data.slice(start, length))

let fd = fs.openSync(file, 'r')
let data2 = new Buffer(length)
let md5sum2 = crypto.createHash('md5')
fs.readSync(fd, data2, 0, length, start)
md5sum2.update(data2)

assert.equal(md5sum.digest('hex'), md5sum2.digest('hex'))