Simple attempt at visual analysis of RNG sources

rng_imager.go

package main

// Inspiration: https://www.random.org/analysis/

import (
        "image"
        "image/color"
        "image/png"
        "math/big"
        "os"

        cr "crypto/rand"
        mr "math/rand"
)

func main() {
        maxSize := 512

        // Using a bad RNG source, aka math/rand
        mathRND := func(max int) int {
                return mr.Intn(max)
        }
        err := GenerateImage(maxSize, "math.png", mathRND)
        if err != nil {
                panic(err)
        }

        // And here's the good one, crypto/rand
        cryptoRND := func(max int) int {
                i, err := cr.Int(cr.Reader, big.NewInt(int64(max)))
                if err != nil {
                        panic(err)
                }
                return int(i.Int64())
        }
        err = GenerateImage(maxSize, "crypto.png", cryptoRND)
        if err != nil {
                panic(err)
        }
}

////////////////////////////////////////////////////////////////////////////////

type RNDFunc func(int) int

func GenerateImage(max int, path string, f RNDFunc) error {
        points := makePoints(max, f)
        img := makeImage(max, points)
        err := saveImage(path, img)
        if err != nil {
                return err
        }
        return nil
}

////////////////////////////////////////////////////////////////////////////////

func makePoints(max int, fn RNDFunc) []image.Point {
        var points []image.Point
        for i := 40000; i > 0; i-- {
                x, y := fn(max), fn(max)
                points = append(points, image.Point{x, y})
        }
        return points
}

func makeImage(max int, points []image.Point) image.Image {
        min := 0
        c := color.Gray{255}
        img := image.NewGray(image.Rect(min, min, max, max))

        for _, p := range points {
                if p.X >= min && p.X <= max && p.Y >= min && p.Y <= max {
                        img.Set(p.X, p.Y, c)
                }
        }
        return img
}

func saveImage(path string, img image.Image) error {
        f, err := os.Create(path)
        if err != nil {
                return err
        }
        defer f.Close()

        if err = png.Encode(f, img); err != nil {
                return err
        }
        return nil
}