support.go

package mctester

//	"github.com/cespare/xxhash"
import (
	"math/rand"
	"strings"
)

// key generator
// value generator
// xxhash

// from: https://stackoverflow.com/questions/22892120/how-to-generate-a-random-string-of-a-fixed-length-in-go
// about as good as I could do, but in less time :P
// using the strings.Builder rather than the unsafe bit.
const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
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
)

// TODO: random string with prefix/postfix/template/something.
// TODO: need wrapper for "key space", so can seed from etc.

// randomized keys!
// TODO: is sb reusable?
func RandString(src rand.Source, n int, prefix string) string {
	sb := strings.Builder{}
	sb.Grow(len(prefix) + n)
	sb.WriteString(prefix)
	// A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
	for i, cache, remain := n-1, src.Int63(), letterIdxMax; i >= 0; {
		if remain == 0 {
			cache, remain = src.Int63(), letterIdxMax
		}
		if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
			sb.WriteByte(letterBytes[idx])
			i--
		}
		cache >>= letterIdxBits
		remain--
	}

	return sb.String()
}

// randomized values!
// FIXME: take a buffer.
func RandBytes(src rand.Source, n int) []byte {
	b := make([]byte, n)
	// A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
	for i, cache, remain := n-1, src.Int63(), letterIdxMax; i >= 0; {
		if remain == 0 {
			cache, remain = src.Int63(), letterIdxMax
		}
		if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
			b[i] = letterBytes[idx]
			i--
		}
		cache >>= letterIdxBits
		remain--
	}

	return b
}