random.go

package random

import (
	"math/rand"
	"sync"
	"time"
)

const (
	bufferSize = 32
	byte2print = `0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_-0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_-0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_-0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_-`
)

var pool = sync.Pool{
	New: func() interface{} {
		return make([]byte, bufferSize)
	},
}

var randomLock sync.Mutex

var auto rand.Source = rand.NewSource(time.Now().UnixNano())

func read(p []byte) {
	var val uint64
	var on uintptr
	div := len(p) / 8

	randomLock.Lock()
	defer randomLock.Unlock()

	for i := 0; i < div; i++ {
		val = uint64(auto.Int63())
		p[on] = byte(val)
		p[on+1] = byte(val >> 8)
		p[on+2] = byte(val >> 16)
		p[on+3] = byte(val >> 24)
		p[on+4] = byte(val >> 32)
		p[on+5] = byte(val >> 40)
		p[on+6] = byte(val >> 48)
		p[on+7] = byte(val >> 56)
		on += 8
	}
	switch uintptr(len(p)) - on {
	case 0:
		return
	case 1:
		p[on] = byte(auto.Int63())
	case 2:
		val = uint64(auto.Int63())
		p[on] = byte(val)
		p[on+1] = byte(val >> 8)
	case 3:
		val = uint64(auto.Int63())
		p[on] = byte(val)
		p[on+1] = byte(val >> 8)
		p[on+2] = byte(val >> 16)
	case 4:
		val = uint64(auto.Int63())
		p[on] = byte(val)
		p[on+1] = byte(val >> 8)
		p[on+2] = byte(val >> 16)
		p[on+3] = byte(val >> 24)
	case 5:
		val = uint64(auto.Int63())
		p[on] = byte(val)
		p[on+1] = byte(val >> 8)
		p[on+2] = byte(val >> 16)
		p[on+3] = byte(val >> 24)
		p[on+4] = byte(val >> 32)
	case 6:
		val = uint64(auto.Int63())
		p[on] = byte(val)
		p[on+1] = byte(val >> 8)
		p[on+2] = byte(val >> 16)
		p[on+3] = byte(val >> 24)
		p[on+4] = byte(val >> 32)
		p[on+5] = byte(val >> 40)
	case 7:
		val = uint64(auto.Int63())
		p[on] = byte(val)
		p[on+1] = byte(val >> 8)
		p[on+2] = byte(val >> 16)
		p[on+3] = byte(val >> 24)
		p[on+4] = byte(val >> 32)
		p[on+5] = byte(val >> 40)
		p[on+6] = byte(val >> 48)
	}
	return
}

func printable(p []byte) {
	var val uint64
	var on uintptr
	div := len(p) / 8
	randomLock.Lock()
	defer randomLock.Unlock()

	for i := 0; i < div; i++ {
		val = uint64(auto.Int63())
		p[on] = byte2print[byte(val)]
		p[on+1] = byte2print[byte(val>>8)]
		p[on+2] = byte2print[byte(val>>16)]
		p[on+3] = byte2print[byte(val>>24)]
		p[on+4] = byte2print[byte(val>>32)]
		p[on+5] = byte2print[byte(val>>40)]
		p[on+6] = byte2print[byte(val>>48)]
		p[on+7] = byte2print[byte(val>>56)]
		on += 8
	}
	switch uintptr(len(p)) - on {
	case 0:
		return
	case 1:
		p[on] = byte2print[byte(auto.Int63())]
	case 2:
		val = uint64(auto.Int63())
		p[on] = byte2print[byte(val)]
		p[on+1] = byte2print[byte(val>>8)]
	case 3:
		val = uint64(auto.Int63())
		p[on] = byte2print[byte(val)]
		p[on+1] = byte2print[byte(val>>8)]
		p[on+2] = byte2print[byte(val>>16)]
	case 4:
		val = uint64(auto.Int63())
		p[on] = byte2print[byte(val)]
		p[on+1] = byte2print[byte(val>>8)]
		p[on+2] = byte2print[byte(val>>16)]
		p[on+3] = byte2print[byte(val>>24)]
	case 5:
		val = uint64(auto.Int63())
		p[on] = byte2print[byte(val)]
		p[on+1] = byte2print[byte(val>>8)]
		p[on+2] = byte2print[byte(val>>16)]
		p[on+3] = byte2print[byte(val>>24)]
		p[on+4] = byte2print[byte(val>>32)]
	case 6:
		val = uint64(auto.Int63())
		p[on] = byte2print[byte(val)]
		p[on+1] = byte2print[byte(val>>8)]
		p[on+2] = byte2print[byte(val>>16)]
		p[on+3] = byte2print[byte(val>>24)]
		p[on+4] = byte2print[byte(val>>32)]
		p[on+5] = byte2print[byte(val>>40)]
	case 7:
		val = uint64(auto.Int63())
		p[on] = byte2print[byte(val)]
		p[on+1] = byte2print[byte(val>>8)]
		p[on+2] = byte2print[byte(val>>16)]
		p[on+3] = byte2print[byte(val>>24)]
		p[on+4] = byte2print[byte(val>>32)]
		p[on+5] = byte2print[byte(val>>40)]
		p[on+6] = byte2print[byte(val>>48)]
	}
	return
}

// String returns a random alphanumeric string given the length parameter.
func String(length int) string {
	if length > bufferSize {
		p := make([]byte, length)
		printable(p)
		return string(p)
	}

	if length <= 0 {
		return ``
	}
	p := pool.Get().([]byte)
	defer pool.Put(p)
	printable(p[0:length])
	return string(p[0:length])
}