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120 lines
4.4 KiB
Markdown
120 lines
4.4 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/DEVRANDOM/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/DEVRANDOM/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/DEVRANDOM/blob/master/LICENSE)
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[](https://github.com/RobTillaart/DEVRANDOM/releases)
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# DEVRANDOM
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Arduino library to wrap a random generator in a stream.
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## Description
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The library implements a stream class that mimics the /dev/random
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device of a Linux system. It can be used for testing with streams.
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## Interface
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### Constructor
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- **DEVRANDOM()** Constructor.
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- **DEVRANDOM(char \* str)** Constructor, seeding with a string of characters.
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- **DEVRANDOM(uint32_t value)** Constructor, seeding with a integer value.
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- **DEVRANDOM(float value)** Constructor, seeding with a float value.
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### Streeam interface
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To read and to reseed the random generator.
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- **int available()** There is always 1 next byte available.
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- **int peek()** will give you next byte.
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- **int read()** will give you next byte and generate a new one.
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- **size_t write(uint8_t data)** data will be used for reseeding the random number generator (RNG), mode 0 and 3.
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In digitalRead and analogRead mode the seed is used to XOR
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the value, so it does have some effect.
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- **size_t write(uint8_t \* buffer, size_t size)** speeds up reseeding
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for some print / println calls.
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- **void flush()** to keep the CI happy.
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As **write()** reseeds the RNG, printing to **DEVRANDOM** will also reseed the RNG.
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E.g. **dr.println("Hello world");** or **dr.println(3.45678);** will reseed DEVRANDOM too.
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See examples.
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If footprint is an issue one could remove the **size_t write(uint8_t \* buffer, size_t size)**
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from the library and implement a stripped version in **write()**.
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Reseeding will become slower but as reseeding is not used that often
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this might be a good trade off.
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### Random generator selection
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- **void useRandom()** use the build in software random number generator. This is the default, but platform dependant.
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- **void useDigitalRead(uint8_t pin)** use digitalRead to read 8 bits from a defined pin.
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One can build a hardware RNG that flips between 0 and 1 very rapidly and unpredictably.
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Connect this signal to the pin and it will be read and generate a random byte.
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The seed value from the write is used as an XOR byte.
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- **void useAnalogRead(uint8_t pin)** use the analogRead to read 8 bits
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This can be fed with any analogue noise source.
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The seed value from the write is used as a XOR byte.
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- **void useMarsaglia()** uses the Marsaglia pseudo random generator.
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This one is quite fast and good, and more important portable.
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- **uint8_t getMode()** returns the source of randomness.
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| Mode | DEVRANDOM_MODE | Type |
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|:-------:|:----------------:|:-----------------------|
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| 0 | build in random | depends on platform |
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| 1 | digitalRead | hardware external |
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| 2 | analogRead | hardware external |
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| 3 | Marsaglia | software portable PRNG |
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There might be other RNG's in the future.
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If you have an interesting and fast PRNG to be included please let me know.
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### Obsolete
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- **useSW()** replaced by **useRandom()**.
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- **useHW(uint8_t pin)** replaced by **useDigitalRead()**.
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- **useAR(uint8_t pin)** replaced by **useAnalogRead()**.
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## Operation
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See example sketches.
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### Example
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As shown in the example one can use fscanf() to read larger data types,
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```cpp
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DEVRANDOM dr;
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uint32_t x;
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fscanf((FILE*) &dr, "%lu", &x);
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Serial.println(x);
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```
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However float is not supported standard in the fscanf() by UNO and strings (%s) generate garbage.
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So a password generator is a bit more difficult (and a good exercise).
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## Future
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- improve documentation.
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- add examples.
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- add other (portable) PRNG.
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- **available()** returns 1,
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- should that be more e.g. INT_MAX
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- a random number > 0 ?
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- ?
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- when changing mode should \_next == **peek()** be reset?
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- yes, think so ```_next = _rnd();```
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- when already in that mode? (=> complex)
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