initial import

core/stringx/random.go

@@ -0,0 +1,79 @@
+package stringx
+
+import (
+	crand "crypto/rand"
+	"fmt"
+	"math/rand"
+	"sync"
+	"time"
+)
+
+const (
+	letterBytes    = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
+	letterIdxBits  = 6 // 6 bits to represent a letter index
+	idLen          = 8
+	defaultRandLen = 8
+	letterIdxMask  = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
+	letterIdxMax   = 63 / letterIdxBits   // # of letter indices fitting in 63 bits
+)
+
+var src = newLockedSource(time.Now().UnixNano())
+
+type lockedSource struct {
+	source rand.Source
+	lock   sync.Mutex
+}
+
+func newLockedSource(seed int64) *lockedSource {
+	return &lockedSource{
+		source: rand.NewSource(seed),
+	}
+}
+
+func (ls *lockedSource) Int63() int64 {
+	ls.lock.Lock()
+	defer ls.lock.Unlock()
+	return ls.source.Int63()
+}
+
+func (ls *lockedSource) Seed(seed int64) {
+	ls.lock.Lock()
+	defer ls.lock.Unlock()
+	ls.source.Seed(seed)
+}
+
+func Rand() string {
+	return Randn(defaultRandLen)
+}
+
+func RandId() string {
+	b := make([]byte, idLen)
+	_, err := crand.Read(b)
+	if err != nil {
+		return Randn(idLen)
+	}
+
+	return fmt.Sprintf("%x%x%x%x", b[0:2], b[2:4], b[4:6], b[6:8])
+}
+
+func Randn(n int) string {
+	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 string(b)
+}
+
+func Seed(seed int64) {
+	src.Seed(seed)
+}