subcoding/test/rand_test.go

package test

import "math"
import "math/bits"
import "testing"

import "github.com/firestuff/subcoding/gen"

func TestRandBiasedUint64(t *testing.T) {
	buckets := [65]uint64{}

	for i := 0; i < 1000000; i++ {
		val := gen.RandBiasedUint64()
		buckets[bits.Len64(val)]++
	}

	var max uint64 = 0
	var min uint64 = math.MaxUint64

	for _, count := range buckets {
		if count > max {
			max = count
		}

		if count < min {
			min = count
		}
	}

	if max - min > max / 10 {
		t.Fatalf("Variance greater than allowed: %d > %d (max=%d min=%d)", max - min, max / 10, max, min)
	}
}

func TestRandBiasedInt64(t *testing.T) {
	// [0,62]: positive
	// [63,63]: zero
	// [64,126]: negative
	buckets := [127]uint64{}

	for i := 0; i < 1000000; i++ {
		val := gen.RandBiasedInt64()
		switch {
		case val == 0:
			buckets[63]++
		case val < 0:
			buckets[63 + bits.Len64(uint64(val * -1))]++
		case val > 0:
			buckets[63 - bits.Len64(uint64(val))]++
		}
	}

	var max uint64 = 0
	var min uint64 = math.MaxUint64

	for _, count := range buckets {
		if count > max {
			max = count
		}

		if count < min {
			min = count
		}
	}

	if max - min > max / 10 {
		t.Fatalf("Variance greater than allowed: %d > %d (max=%d min=%d)", max - min, max / 10, max, min)
	}
}