ee56d93454
[ Merge of http://go/wvgerrit/84607 ] [ Merge of http://go/wvgerrit/84608 ] The primary goal is to replace the use of `rand()` with the random number generators provided with the C++11 standard. This simplified generator wraps some of the technical aspects of the <random> library and provides an interface for uniformly distributed integers. As part of the `rand()` purge in the CDM, all uses of the C random int function in `core()` have been removed. Places that previously used `rand()` now use `CdmRandom` facilities. Test: Linux unittest and Android unittest Bug: 130680365 Change-Id: Ica383870536ed462dbb80e630c2d66845e38b937
110 lines
3.9 KiB
C++
110 lines
3.9 KiB
C++
// Copyright 2019 Google LLC. All Rights Reserved. This file and proprietary
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// source code may only be used and distributed under the Widevine Master
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// License Agreement.
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#ifndef WVCDM_CORE_CDM_RANDOM_H_
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#define WVCDM_CORE_CDM_RANDOM_H_
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#include <mutex>
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#include <random>
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#include <string>
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namespace wvcdm {
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// CdmRandomGenerator is a thread safe, pseudo-random number generator.
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// It's purpose is to simplified interface for C++11's <random> library.
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// Some of the methods use a "device specific" random seed, if the
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// compiler/device does not support device specific randomizers, then the
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// actual value supplied may not be random.
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class CdmRandomGenerator {
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public:
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// The maximum number of bytes that can be generated at once for
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// `RandomData()`.
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static constexpr size_t kMaxRandomDataLength = 8192; // 8 kB
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// Initializes the pseudo-random generator with a value from a device
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// specific random number generator.
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CdmRandomGenerator();
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// Initializes the pseudo-random generator with the specified seed value.
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explicit CdmRandomGenerator(unsigned int seed) : generator_(seed) {}
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// All of these methods are thread-safe.
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// Seeds the pseudo-random generator with a value from a device specific
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// random number generator.
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void Seed();
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// Seeds the pseudo-random generator with the specified seed value.
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// This is somewhat similar to `srand()` from the C standard library;
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// except that the sequence generated from successive calls to `Rand()`
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// will not necessarily be the same as they would be from the
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// standard library `rand()`. This is due to the underlying pseudo-random
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// generator that is used.
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void Seed(unsigned int seed);
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// Returns a pseudo-random integer.
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// This is similar to `rand()` from the C standard library. The integer
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// returned is in the range of [0, RAND_MAX].
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int Rand();
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// Allows for RNG to be callable, this is to make it similar to the
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// C++11 generator interfaces.
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int operator()() { return Rand(); }
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// Returns a pseudo-random integer within the provided inclusive range.
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uint64_t RandomInRange(uint64_t lower, uint64_t upper);
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uint64_t RandomInRange(uint64_t upper) { return RandomInRange(0, upper); }
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// Returns a byte string containing randomized bytes of the specified
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// length.
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// If |length| is greater than |CdmRandomGenerator::kMaxRandomDataLength|,
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// then an error is logged and an empty string is returned.
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std::string RandomData(size_t length);
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// Random true/false using Bernoulli distribution of equal probability.
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bool RandomBool();
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private:
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// Mutex is used to lock the object, and allowing it to be used
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// concurrently in different threads.
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std::mutex generator_lock_;
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// The `default_random_engine` depends on the compiler used and
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// potentially its version. This is important to know if you need to
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// create reproducible tests between platforms.
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std::default_random_engine generator_;
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};
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// Provides a static interface to a process-wide instance of
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// CdmRandomGenerator.
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class CdmRandom {
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public:
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static int Rand() { return GetInstance()->Rand(); }
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static uint64_t RandomInRange(uint64_t lower, uint64_t upper) {
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return GetInstance()->RandomInRange(lower, upper);
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}
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static uint64_t RandomInRange(uint64_t upper) {
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return GetInstance()->RandomInRange(upper);
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}
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static std::string RandomData(size_t length) {
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return GetInstance()->RandomData(length);
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}
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static bool RandomBool() { return GetInstance()->RandomBool(); }
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private:
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// These are intended to be used by tests if needed.
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static void Seed(unsigned int seed) { GetInstance()->Seed(seed); }
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static void Seed() { GetInstance()->Seed(); }
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// Returns the process-wide instance of CdmRandomGenerator.
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// It the global instance has not yet been created, then a new instance
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// is created using a device-specific random seed.
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static CdmRandomGenerator* GetInstance();
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};
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} // namespace wvcdm
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#endif // WVCDM_CORE_CDM_RANDOM_H_
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