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// Copyright 2015, Joe Tsai. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE.md file.
package testutil
import (
"crypto/aes"
"crypto/cipher"
"encoding/binary"
)
// Rand implements a deterministic pseudo-random number generator.
// This differs from the math.Rand in that the exact output will be consistent
// across different versions of Go.
type Rand struct {
cipher.Block
blk [aes.BlockSize]byte
}
func NewRand(seed int) *Rand {
var key [aes.BlockSize]byte
binary.LittleEndian.PutUint64(key[:], uint64(seed))
r, _ := aes.NewCipher(key[:])
return &Rand{Block: r}
}
func (r *Rand) Int() int {
r.Encrypt(r.blk[:], r.blk[:])
return int(binary.BigEndian.Uint32(r.blk[:]) >> 1)
}
func (r *Rand) Intn(n int) int {
return r.Int() % n
}
func (r *Rand) Bytes(n int) []byte {
b := make([]byte, n)
bb := b
for len(bb) > 0 {
r.Encrypt(r.blk[:], r.blk[:])
cnt := copy(bb, r.blk[:])
bb = bb[cnt:]
}
return b
}
func (r *Rand) Perm(n int) []int {
m := make([]int, n)
for i := 0; i < n; i++ {
j := r.Intn(i + 1)
m[i] = m[j]
m[j] = i
}
return m
}
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