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random: factor out rand32_distribute() from RandomAPI::randrange32()

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This is done so that rand32_distribute() can be used for
hash seeds as well.

Signed-off-by: James Yonan <james@openvpn.net>
This commit is contained in:
James Yonan 2019-07-18 17:44:51 -06:00
parent 90123495a5
commit 60501b4513
2 changed files with 59 additions and 10 deletions
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32
openvpn/random/randapi.hpp
View File

@ -30,6 +30,7 @@
#include <openvpn/common/size.hpp>
#include <openvpn/common/rc.hpp>
#include <openvpn/common/exception.hpp>
#include <openvpn/random/randistrib.hpp>
namespace openvpn {
@ -85,16 +86,6 @@ namespace openvpn {
return rand_get_positive<T>() % end;
}
// Return a uniformly distributed random number in the range [0, end).
// This version is strictly 32-bit only and optimizes by avoiding
// integer division.
std::uint32_t randrange32(const std::uint32_t end)
{
std::uint32_t r;
rand_fill(r);
return (std::uint64_t(r) * end) >> 32;
}
// Return a uniformly distributed random number in the range [start, end].
template <typename T>
T randrange(const T start, const T end)
@ -105,6 +96,27 @@ namespace openvpn {
return start + rand_get_positive<T>() % (end - start + 1);
}
// Return a uniformly distributed random number in the range [0, end).
// This version is strictly 32-bit only and optimizes by avoiding
// integer division.
std::uint32_t randrange32(const std::uint32_t end)
{
std::uint32_t r;
rand_fill(r);
return rand32_distribute(r, end);
}
// Return a uniformly distributed random number in the range [start, end].
// This version is strictly 32-bit only and optimizes by avoiding
// integer division.
std::uint32_t randrange32(const std::uint32_t start, const std::uint32_t end)
{
if (start >= end)
return start;
else
return start + randrange32(end - start + 1);
}
// Throw an exception if algorithm is not crypto-strength.
// Be sure to always call this method before using an rng
// for crypto purposes.

37
openvpn/random/randistrib.hpp Normal file
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@ -0,0 +1,37 @@
// OpenVPN -- An application to securely tunnel IP networks
// over a single port, with support for SSL/TLS-based
// session authentication and key exchange,
// packet encryption, packet authentication, and
// packet compression.
//
// Copyright (C) 2012-2019 OpenVPN Inc.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License Version 3
// as published by the Free Software Foundation.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program in the COPYING file.
// If not, see <http://www.gnu.org/licenses/>.
#pragma once
#include <cstdint>
namespace openvpn {
// Return a uniformly distributed random number in the range [0, end)
// using seed as a random seed. This version is strictly 32-bit only
// and optimizes by avoiding integer division.
inline std::uint32_t rand32_distribute(const std::uint32_t seed,
const std::uint32_t end)
{
return (std::uint64_t(seed) * end) >> 32;
}
}