Optimize randBool() and randString()

[jake-ciolek]

I love this library, small but gets the job done! :)

I have tinkered a bit with the functions to generate bools and strings and made them a bit faster. Hopefully it will save someone some clocks when running tests.

The code speeds up bool generation 3-fold. I've ran some benchmarks on GCP VM's and my local MacBook:

My MacBook Pro:

BenchmarkRandBool-8 75312272 14.5 ns/op
BenchmarkRandBoolNew-8 235223112 5.06 ns/op
BenchmarkRandStringStock-8 1439635 841 ns/op
BenchmarkRandStringBuilder-8 1541736 775 ns/op

8 core GCP E2:

BenchmarkRandBool-8 70003590 16.6 ns/op
BenchmarkRandBoolNew-8 236062108 5.08 ns/op
BenchmarkRandStringStock-8 1370116 874 ns/op
BenchmarkRandStringBuilder-8 1484086 807 ns/op

8 core GCP N2 (Intel Cascade Lake):

BenchmarkRandBool-8 91276062 13.1 ns/op
BenchmarkRandBoolNew-8 301435986 3.98 ns/op
BenchmarkRandStringStock-8 1743852 688 ns/op
BenchmarkRandStringBuilder-8 1883102 638 ns/op

8 core GCP N1 (Intel Skylake):

BenchmarkRandBool-8 71896552 16.5 ns/op
BenchmarkRandBoolNew-8 239149131 5.03 ns/op
BenchmarkRandStringStock-8 1375860 873 ns/op
BenchmarkRandStringBuilder-8 1484378 808 ns/op

randString() will be 5-7% due to less data being moved around (thanks to strings.Builder)

randString() memory usage change:

BenchmarkRandStringStock-8 1543179 772 ns/op 71 B/op 1 allocs/op
BenchmarkRandStringBuilder-8 1639436 735 ns/op 48 B/op 1 allocs/op

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[jake-ciolek]

@googlebot I signed it!

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CLAs look good, thanks!

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[lavalamp]

Why bit 31 and not some other bit?

[jake-ciolek]

I had to pick one and I believe there was no better choice :)

[lavalamp]

Yeah, they should all be the same. I just wasn't sure if the change from bit 0 was significant for the speed up--it shouldn't be, right?

[jake-ciolek]

From my benchmarks, on my local machine I've found this bit to be faster from bit 0 by 1-2% - why, I don't know - probably some CPU arch black magic.

[lavalamp]

hm... you can use https://godoc.org/golang.org/x/tools/cmd/benchcmp to tell if it's significant or not. (not shown in the help: you can put multiple runs in both the old and new file and it will give you the std dev so you can tell if it's significant or not)

[lavalamp]

Thanks! Can you add your benchmark, too?

[jake-ciolek]

Sure!

import (
	"math/rand"

	"testing"
	"strings"
)

func randBoolOld(r *rand.Rand) bool {
	if r.Int()&1 == 1 {
		return true
	}
	return false
}

func randBoolNew(r *rand.Rand) bool {
	return r.Int31()&(1<<30) == 0
}

func randStringOld(r *rand.Rand) string {
	n := r.Intn(20)
	runes := make([]rune, n)
	for i := range runes {
		runes[i] = unicodeRanges[r.Intn(len(unicodeRanges))].choose(r)
	}
	return string(runes)
}

func randStringBuilder(r *rand.Rand) string {
	n := r.Intn(20)
	sb := strings.Builder{}
        sb.Grow(n)
	for i := 0 ;i<n; i++ {
                sb.WriteRune(unicodeRanges[r.Intn(len(unicodeRanges))].choose(r))
	}
	
	return sb.String()
}

type int63nPicker interface {
	Int63n(int64) int64
}

type charRange struct {
	first, last rune
}

// choose returns a random unicode character from the given range, using the
// given randomness source.
func (cr charRange) choose(r int63nPicker) rune {
	count := int64(cr.last - cr.first + 1)
	return cr.first + rune(r.Int63n(count))
}

var unicodeRanges = []charRange{
	{' ', '~'},           // ASCII characters
	{'\u00a0', '\u02af'}, // Multi-byte encoded characters
	{'\u4e00', '\u9fff'}, // Common CJK (even longer encodings)
}

func BenchmarkRandBool(b *testing.B) {
	rs := rand.New(rand.NewSource(123))
	for i := 0; i < b.N; i++ {
		randBoolOld(rs)
    }
}

func BenchmarkRandBoolNew(b *testing.B) {
	rs := rand.New(rand.NewSource(123))
	for i := 0; i < b.N; i++ {
		randBoolNew(rs)
    }
}

func BenchmarkRandStringStock(b *testing.B) {
	rs := rand.New(rand.NewSource(123))
	for i := 0; i < b.N; i++ {
		randStringOld(rs)
    }
}

func BenchmarkRandStringBuilder(b *testing.B) {
	rs := rand.New(rand.NewSource(123))
	for i := 0; i < b.N; i++ {
		randStringBuilder(rs)
    }
}

[lavalamp]

Can you add the benchmarks to the _test.go file? (just one for Bool and one for String; no need for old/new--we can just track that over time)

[jake-ciolek]

Added benchmarks :)

[lavalamp]

Looks good-- can you run gofmt?

[jake-ciolek]

Done 😃

[lavalamp]

I bet n*2 or n*3 would avoid an extra allocation or two.

[lavalamp]

LGTM thanks!