83 lines
2 KiB
Go
83 lines
2 KiB
Go
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package gago
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import (
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"fmt"
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"math/rand"
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"time"
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)
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// newRandomNumberGenerator returns a new random number generator with a random
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// seed.
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func newRandomNumberGenerator() *rand.Rand {
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return rand.New(rand.NewSource(time.Now().UnixNano()))
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}
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// Sample k unique integers in range [min, max) using reservoir sampling,
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// specifically Vitter's Algorithm R.
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func randomInts(k, min, max int, rng *rand.Rand) (ints []int) {
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ints = make([]int, k)
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for i := 0; i < k; i++ {
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ints[i] = i + min
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}
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for i := k; i < max-min; i++ {
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var j = rng.Intn(i + 1)
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if j < k {
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ints[j] = i + min
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}
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}
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return
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}
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// Sample k unique integers from a slice of n integers without replacement.
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func sampleInts(ints []int, k int, rng *rand.Rand) ([]int, []int, error) {
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if k > len(ints) {
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return nil, nil, fmt.Errorf("Cannot sample %d elements from array of length %d", k, len(ints))
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}
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var (
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sample = make([]int, k)
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idxs = make([]int, k)
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)
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for i, idx := range randomInts(k, 0, len(ints), rng) {
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sample[i] = ints[idx]
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idxs[i] = idx
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}
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return sample, idxs, nil
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}
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// Generate random weights that sum up to 1.
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func randomWeights(size int) []float64 {
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var (
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weights = make([]float64, size)
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total float64
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)
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for i := range weights {
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weights[i] = rand.Float64()
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total += weights[i]
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}
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var normalized = divide(weights, total)
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return normalized
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}
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const (
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letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
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letterIdxBits = 6 // 6 bits to represent a letter index
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letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
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letterIdxMax = 63 / letterIdxBits // # of letter indices fitting in 63 bits
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)
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func randString(n int, rng *rand.Rand) string {
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b := make([]byte, n)
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for i, cache, remain := n-1, rng.Int63(), letterIdxMax; i >= 0; {
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if remain == 0 {
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cache, remain = rng.Int63(), letterIdxMax
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}
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if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
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b[i] = letterBytes[idx]
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i--
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}
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cache >>= letterIdxBits
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remain--
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}
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return string(b)
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}
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