rand

rand/fast_rand_generator.go

@@ -0,0 +1,78 @@
+package rand
+
+import (
+	_ "unsafe"
+)
+
+var fastGenerator = &fastRandGenerator{}
+
+type fastRandGenerator struct {
+}
+
+func NewFastRandGenerator() *fastRandGenerator {
+	return fastGenerator
+}
+
+func (*fastRandGenerator) Int63() int64 {
+	uu := uint64(uint64(Fastrand())<<32) ^ uint64(Fastrand())
+	return int64(uu << 1 >> 1)
+}
+
+func (r *fastRandGenerator) Int63n(n int64) int64 {
+	if n <= 0 {
+		panic("invalid argument to Int63n")
+	}
+
+	if n&(n-1) == 0 { // n is power of two, can mask
+		return r.Int63() & (n - 1)
+	}
+	max := int64((1 << 63) - 1 - (1<<63)%uint64(n))
+	v := r.Int63()
+	for v > max {
+		v = r.Int63()
+	}
+
+	return v % n
+}
+
+func (*fastRandGenerator) Int31() int32 {
+	u := Fastrand()
+	return int32(u << 1 >> 1)
+}
+
+func (r fastRandGenerator) Int31n(n int32) int32 {
+	if n <= 0 {
+		panic("invalid argument to Int31n")
+	}
+
+	if n&(n-1) == 0 { // n is power of two, can mask
+		return r.Int31() & (n - 1)
+	}
+
+	max := int32((1 << 31) - 1 - (1<<31)%uint32(n))
+	v := r.Int31()
+	for v > max {
+		v = r.Int31()
+	}
+
+	return v % n
+}
+
+func (*fastRandGenerator) Int() int {
+	u := Fastrand()
+	return int(u << 1 >> 1)
+}
+
+func (r *fastRandGenerator) Intn(n int) int {
+	if n <= 0 {
+		panic("invalid argument to Intn")
+	}
+	if n <= 1<<31-1 {
+		return int(r.Int31n(int32(n)))
+	}
+
+	return int(r.Int63n(int64(n)))
+}
+
+//go:linkname Fastrand runtime.fastrand
+func Fastrand() uint32