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/**
* TrueRandom - A true random number generator for Arduino.
*
* Copyright (c) 2010 Peter Knight, Tinker.it! All rights reserved.
*/
#include <avr/io.h>
#include "TrueRandom.h"
int TrueRandomClass::randomBitRaw(void) {
uint8_t copyAdmux, copyAdcsra, copyAdcsrb, copyPortc, copyDdrc;
uint16_t i;
uint8_t bit;
volatile uint8_t dummy;
// Store all the registers we'll be playing with
copyAdmux = ADMUX;
copyAdcsra = ADCSRA;
copyAdcsrb = ADCSRB;
copyPortc = PORTC;
copyDdrc = DDRC;
// Perform a conversion on Analog0, using the Vcc reference
ADMUX = _BV(REFS0);
#if F_CPU > 16000000
// ADC is enabled, divide by 32 prescaler
ADCSRA = _BV(ADEN) | _BV(ADPS2) | _BV(ADPS0);
#elif F_CPU > 8000000
// ADC is enabled, divide by 16 prescaler
ADCSRA = _BV(ADEN) | _BV(ADPS2);
#else
// ADC is enabled, divide by 8 prescaler
ADCSRA = _BV(ADEN) | _BV(ADPS1) | _BV(ADPS0);
#endif
// Autotriggering disabled
ADCSRB = 0;
// Pull Analog0 to ground
PORTC &=~_BV(0);
DDRC |= _BV(0);
// Release Analog0, apply internal pullup
DDRC &= ~_BV(0);
PORTC |= _BV(1);
// Immediately start a sample conversion on Analog0
ADCSRA |= _BV(ADSC);
// Wait for conversion to complete
while (ADCSRA & _BV(ADSC)) PORTC ^= _BV(0);
// Xor least significant bits together
bit = ADCL;
// We're ignoring the high bits, but we have to read them before the next conversion
dummy = ADCH;
// Restore register states
ADMUX = copyAdmux;
ADCSRA = copyAdcsra;
ADCSRB = copyAdcsrb;
PORTC = copyPortc;
DDRC = copyDdrc;
return bit & 1;
}
int TrueRandomClass::randomBitRaw2(void) {
// Software whiten bits using Von Neumann algorithm
//
// von Neumann, John (1951). "Various techniques used in connection
// with random digits". National Bureau of Standards Applied Math Series
// 12:36.
//
for(;;) {
int a = randomBitRaw() | (randomBitRaw()<<1);
if (a==1) return 0; // 1 to 0 transition: log a zero bit
if (a==2) return 1; // 0 to 1 transition: log a one bit
// For other cases, try again.
}
}
int TrueRandomClass::randomBit(void) {
// Software whiten bits using Von Neumann algorithm
//
// von Neumann, John (1951). "Various techniques used in connection
// with random digits". National Bureau of Standards Applied Math Series
// 12:36.
//
for(;;) {
int a = randomBitRaw2() | (randomBitRaw2()<<1);
if (a==1) return 0; // 1 to 0 transition: log a zero bit
if (a==2) return 1; // 0 to 1 transition: log a one bit
// For other cases, try again.
}
}
char TrueRandomClass::randomByte(void) {
char result;
uint8_t i;
result = 0;
for (i=8; i--;) result += result + randomBit();
return result;
}
int TrueRandomClass::rand() {
int result;
uint8_t i;
result = 0;
for (i=15; i--;) result += result + randomBit();
return result;
}
long TrueRandomClass::random() {
long result;
uint8_t i;
result = 0;
for (i=31; i--;) result += result + randomBit();
return result;
}
long TrueRandomClass::random(long howBig) {
long randomValue;
long maxRandomValue;
long topBit;
long bitPosition;
if (!howBig) return 0;
randomValue = 0;
if (howBig & (howBig-1)) {
// Range is not a power of 2 - use slow method
topBit = howBig-1;
topBit |= topBit>>1;
topBit |= topBit>>2;
topBit |= topBit>>4;
topBit |= topBit>>8;
topBit |= topBit>>16;
topBit = (topBit+1) >> 1;
bitPosition = topBit;
do {
// Generate the next bit of the result
if (randomBit()) randomValue |= bitPosition;
// Check if bit
if (randomValue >= howBig) {
// Number is over the top limit - start again.
randomValue = 0;
bitPosition = topBit;
} else {
// Repeat for next bit
bitPosition >>= 1;
}
} while (bitPosition);
} else {
// Special case, howBig is a power of 2
bitPosition = howBig >> 1;
while (bitPosition) {
if (randomBit()) randomValue |= bitPosition;
bitPosition >>= 1;
}
}
return randomValue;
}
long TrueRandomClass::random(long howSmall, long howBig) {
if (howSmall >= howBig) return howSmall;
long diff = howBig - howSmall;
return TrueRandomClass::random(diff) + howSmall;
}
void TrueRandomClass::memfill(char* location, int size) {
for (;size--;) *location++ = randomByte();
}
void TrueRandomClass::mac(uint8_t* macLocation) {
memfill((char*)macLocation,6);
}
void TrueRandomClass::uuid(uint8_t* uuidLocation) {
// Generate a Version 4 UUID according to RFC4122
memfill((char*)uuidLocation,16);
// Although the UUID contains 128 bits, only 122 of those are random.
// The other 6 bits are fixed, to indicate a version number.
uuidLocation[6] = 0x40 | (0x0F & uuidLocation[6]);
uuidLocation[8] = 0x80 | (0x3F & uuidLocation[8]);
}
TrueRandomClass TrueRandom;
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