About

goos: linux
goarch: amd64
pkg: rndstr
BenchmarkGetBytes48-4     	10000000	 176 ns/op		  48 B/op	1 allocs/op
BenchmarkGetBytes1500-4   	  300000	4863 ns/op		1536 B/op	1 allocs/op
PASS

rndstr.go

// A fast random []byte generator. The default Source is used, which
// is safe for concurrent use by multiple goroutines. The default Source
// is seeded at package init.
package rndstr

import (
  "math/rand"
  "time"
)

func init() {
  rand.Seed(time.Now().UnixNano())
}

const letterBytes = "1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-_"
const (
  letterIdxBits = 6                    // 6 bits to represent a letter index
  letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
  letterIdxMax  = 63 / letterIdxBits   // # of letter indices fitting in 63 bits
)

// Fills the []byte with random characters
func PutBytes(b []byte) {
  n := len(b)
  for i, cache, remain := n-1, rand.Int63(), letterIdxMax; i >= 0; {
    if remain == 0 {
      cache, remain = rand.Int63(), letterIdxMax
    }
    idx := int(cache & letterIdxMask)
    b[i] = letterBytes[idx]
    i--
    cache >>= letterIdxBits
    remain--
  }
}

// Returns []byte of 'n' length filled with random characters
func GetBytes(n int) []byte {
  b := make([]byte, n)
  PutBytes(b)
  return b
}

rndstr_test.go

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package rndstr

import "testing"

func TestGetBytes(t *testing.T) {
  randomBytes := GetBytes(1064)
  t.Logf("%s", randomBytes)
}

func TestPutBytes(t *testing.T) {
  randomBytes := make([]byte, 72)
  PutBytes(randomBytes)
  t.Logf("%s", randomBytes)
}

var result []byte

func BenchmarkGetBytes48(b *testing.B) {
  b.ReportAllocs()
  var r []byte
  for n := 0; n < b.N; n++ {
    r = GetBytes(48)
  }
  result = r
}

func BenchmarkGetBytes1500(b *testing.B) {
  b.ReportAllocs()
  var r []byte
  for n := 0; n < b.N; n++ {
    r = GetBytes(1500)
  }
  result = r
}