package rand import ( crand "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 { _, _ = crand.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 { _, _ = crand.Read(r.buf[:]) return int64(binary.BigEndian.Uint64(r.buf[:]) & ^uint64(1<<63)) } // Int31n copied from the standard library math/rand implementation of Int31n 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 } // Int63n copied from the standard library math/rand implementation of Int63n 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 } // Shuffle copied from the standard library math/rand implementation of Shuffle func (r *Rand) Shuffle(n int, swap func(i, j int)) { if n < 0 { panic("invalid argument to Shuffle") } // Fisher-Yates shuffle: https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle // Shuffle really ought not be called with n that doesn't fit in 32 bits. // Not only will it take a very long time, but with 2³¹! possible permutations, // there's no way that any PRNG can have a big enough internal state to // generate even a minuscule percentage of the possible permutations. // Nevertheless, the right API signature accepts an int n, so handle it as best we can. i := n - 1 for ; i > 1<<31-1-1; i-- { j := int(r.Int63n(int64(i + 1))) swap(i, j) } for ; i > 0; i-- { j := int(r.Int31n(int32(i + 1))) swap(i, j) } }