micro/util/rand/rand.go
Vasiliy Tolstov 5596345382 util/rand: replace all non crypto rand stuff with own rand package
Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>
2021-02-18 12:44:18 +03:00

85 lines
1.7 KiB
Go

package rand
import (
"crypto/rand"
"encoding/binary"
)
// Rand is a wrapper around crypto/rand that adds some convenience functions known from math/rand.
type Rand struct {
buf [8]byte
}
func (r *Rand) Int31() int32 {
rand.Read(r.buf[:4])
return int32(binary.BigEndian.Uint32(r.buf[:4]) & ^uint32(1<<31))
}
func (r *Rand) Int() int {
u := uint(r.Int63())
return int(u << 1 >> 1) // clear sign bit if int == int32
}
func (r *Rand) Float64() float64 {
again:
f := float64(r.Int63()) / (1 << 63)
if f == 1 {
goto again // resample; this branch is taken O(never)
}
return f
}
func (r *Rand) Float32() float32 {
again:
f := float32(r.Float64())
if f == 1 {
goto again // resample; this branch is taken O(very rarely)
}
return f
}
func (r *Rand) Uint32() uint32 {
return uint32(r.Int63() >> 31)
}
func (r *Rand) Uint64() uint64 {
return uint64(r.Int63())>>31 | uint64(r.Int63())<<32
}
func (r *Rand) Intn(n int) int {
if n <= 1<<31-1 {
return int(r.Int31n(int32(n)))
}
return int(r.Int63n(int64(n)))
}
func (r *Rand) Int63() int64 {
rand.Read(r.buf[:])
return int64(binary.BigEndian.Uint64(r.buf[:]) & ^uint64(1<<63))
}
// copied from the standard library math/rand implementation of Int63n
func (r *Rand) Int31n(n int32) int32 {
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 (r *Rand) Int63n(n int64) int64 {
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
}