package main

import (
    "crypto/rand"
    "io"
    "testing"
    "strconv"
    "bufio"
)

var sz = []int{1, 4, 8, 16, 32, 64}
var cr, bcr io.Reader

func init() {
    cr = rand.Reader
    bcr = bufio.NewReader(rand.Reader)
}

func BenchmarkCryptoRandRead(b *testing.B) {
    rand.Reader = cr
    b.Run("raw", benchmark)
    rand.Reader = bcr
    b.Run("buffered", benchmark)
}

func benchmark(b *testing.B) {
    defer func() {
        rand.Reader = cr
    }()
    for _, s := range sz {
        buf := make([]byte, s)
        b.Run(strconv.Itoa(s), func (b *testing.B) {
            for i := 0; i < b.N; i++ {
                if n, err := rand.Read(buf); n != s || err != nil {
                    b.Fatal("error in rand.Read()")
                }
            }
        })
        _ = buf
    }
}