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/*
* Copyright (c) 2014, Yawning Angel <yawning at torproject dot org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
// Package csrand implements the math/rand interface over crypto/rand, along
// with some utility functions for common random number/byte related tasks.
//
// Not all of the convinience routines are replicated, only those that are
// useful for obfs4. The CsRand variable provides access to the full math/rand
// API.
package csrand
import (
cryptRand "crypto/rand"
"encoding/binary"
"fmt"
"math/rand"
)
var (
csRandSourceInstance csRandSource
// CsRand is a math/rand instance backed by crypto/rand CSPRNG.
CsRand = rand.New(csRandSourceInstance)
)
type csRandSource struct {
// This does not keep any state as it is backed by crypto/rand.
}
func (r csRandSource) Int63() int64 {
var src [8]byte
err := Bytes(src[:])
if err != nil {
panic(err)
}
val := binary.BigEndian.Uint64(src[:])
val &= (1<<63 - 1)
return int64(val)
}
func (r csRandSource) Seed(seed int64) {
// No-op.
}
// Float64 returns, as a float 64, a pesudo random number in [0.0,1.0).
func Float64() float64 {
return CsRand.Float64()
}
// IntRange returns a uniformly distributed int [min, max].
func IntRange(min, max int) int {
if max < min {
panic(fmt.Sprintf("IntRange: min > max (%d, %d)", min, max))
}
r := (max + 1) - min
ret := CsRand.Intn(r)
return ret + min
}
// Bytes fills the slice with random data.
func Bytes(buf []byte) error {
n, err := cryptRand.Read(buf)
if err != nil {
// Yes, the go idiom is to check the length, but we panic() when it
// does not match because the system is screwed at that point.
return err
} else if n != len(buf) {
panic(fmt.Sprintf("Bytes: truncated rand.Read (%d, %d)", n, len(buf)))
}
return nil
}
/* vim :set ts=4 sw=4 sts=4 noet : */
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