12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656667686970717273747576777879808182 |
- package gago
- import (
- "fmt"
- "math/rand"
- "time"
- )
- // newRandomNumberGenerator returns a new random number generator with a random
- // seed.
- func newRandomNumberGenerator() *rand.Rand {
- return rand.New(rand.NewSource(time.Now().UnixNano()))
- }
- // Sample k unique integers in range [min, max) using reservoir sampling,
- // specifically Vitter's Algorithm R.
- func randomInts(k, min, max int, rng *rand.Rand) (ints []int) {
- ints = make([]int, k)
- for i := 0; i < k; i++ {
- ints[i] = i + min
- }
- for i := k; i < max-min; i++ {
- var j = rng.Intn(i + 1)
- if j < k {
- ints[j] = i + min
- }
- }
- return
- }
- // Sample k unique integers from a slice of n integers without replacement.
- func sampleInts(ints []int, k int, rng *rand.Rand) ([]int, []int, error) {
- if k > len(ints) {
- return nil, nil, fmt.Errorf("Cannot sample %d elements from array of length %d", k, len(ints))
- }
- var (
- sample = make([]int, k)
- idxs = make([]int, k)
- )
- for i, idx := range randomInts(k, 0, len(ints), rng) {
- sample[i] = ints[idx]
- idxs[i] = idx
- }
- return sample, idxs, nil
- }
- // Generate random weights that sum up to 1.
- func randomWeights(size int) []float64 {
- var (
- weights = make([]float64, size)
- total float64
- )
- for i := range weights {
- weights[i] = rand.Float64()
- total += weights[i]
- }
- var normalized = divide(weights, total)
- return normalized
- }
- const (
- letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
- 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
- )
- func randString(n int, rng *rand.Rand) string {
- b := make([]byte, n)
- for i, cache, remain := n-1, rng.Int63(), letterIdxMax; i >= 0; {
- if remain == 0 {
- cache, remain = rng.Int63(), letterIdxMax
- }
- if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
- b[i] = letterBytes[idx]
- i--
- }
- cache >>= letterIdxBits
- remain--
- }
- return string(b)
- }
|