30 lines
623 B
Go
30 lines
623 B
Go
package utils
|
|
|
|
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 [4]byte
|
|
}
|
|
|
|
func (r *Rand) Int31() int32 {
|
|
rand.Read(r.buf[:])
|
|
return int32(binary.BigEndian.Uint32(r.buf[:]) & ^uint32(1<<31))
|
|
}
|
|
|
|
// 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
|
|
}
|