Comments on: Random number generation on 8-bit AVR http://www.reenigne.org/blog/random-number-generation-on-8-bit-avr/ Stuff I think about Sun, 22 Jan 2012 21:39:31 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: Andrew http://www.reenigne.org/blog/random-number-generation-on-8-bit-avr/comment-page-1/#comment-3999 Andrew Fri, 25 Feb 2011 03:36:58 +0000 http://www.reenigne.org/blog/?p=1159#comment-3999 Yes, you can do it that way too but an 8x8 bit multiply is only 2 cycles on 8-bit AVR so there isn't so much advantage to avoiding LCGs. You also still need to do the "mod N" opreation. Also, a routine with 8 bits of state would not have been enough for this application - it would have repeated too quickly and lower-numbered LEDs would have shown up significantly more often than lower-numbered ones. Yes, you can do it that way too but an 8x8 bit multiply is only 2 cycles on 8-bit AVR so there isn't so much advantage to avoiding LCGs. You also still need to do the "mod N" opreation. Also, a routine with 8 bits of state would not have been enough for this application - it would have repeated too quickly and lower-numbered LEDs would have shown up significantly more often than lower-numbered ones.

]]> By: Richard B. Johnson http://www.reenigne.org/blog/random-number-generation-on-8-bit-avr/comment-page-1/#comment-3998 Richard B. Johnson Fri, 25 Feb 2011 01:27:49 +0000 http://www.reenigne.org/blog/?p=1159#comment-3998 Simple 8-bit RNG in 'C' //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- // // 8-bit random number generator. // // Copyright 2011 Richard B. Johnson // rjohnson@Route495Software.com // // You can use this if you preserve the Copyright notice above. // #include #if !defined(uint8_t) typedef unsigned char uint8_t; #endif static uint8_t Seed = 0x00; static uint8_t Magic = 0x5c; //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- // // This, using the 'C' language, rotates all the bits in val to the right // the number of bits in nr. // static uint8_t RotateRight(uint8_t val, int nr) { uint8_t tmp; while(nr--) { tmp = val & 1; tmp <>= 1; val |= tmp; } return val; } //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- // // Ths pseudo random number generator. // uint8_t Rand() { Seed = RotateRight(Seed, 3); Seed += Magic; return Seed; } //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- // // Seed the random number generator. // void Srand(uint8_t val) { Seed = val; } //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- // // This is for testing. Define SETUP to find tha correct magic number // to hard-code. // #define TESTING #ifdef TESTING #define NoSETUP int main() { int i; #ifdef SETUP for(;;) { Seed = 0; printf("%02x\n", Magic); i = 0; while(Rand()) i++; if(i < 0xfe) Magic++; else break; } #else for(i=0; i< 0xff; i++) printf("%02x\n", Rand()); #endif return 0; } #endif //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Simple 8-bit RNG in 'C'

//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
//
// 8-bit random number generator.
//
// Copyright 2011 Richard B. Johnson
// rjohnson@Route495Software.com
//
// You can use this if you preserve the Copyright notice above.
//
#include

#if !defined(uint8_t)
typedef unsigned char uint8_t;
#endif

static uint8_t Seed = 0x00;
static uint8_t Magic = 0x5c;

//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
//
// This, using the 'C' language, rotates all the bits in val to the right
// the number of bits in nr.
//

static uint8_t RotateRight(uint8_t val, int nr)
{
uint8_t tmp;
while(nr--)
{
tmp = val & 1;
tmp <>= 1;
val |= tmp;
}
return val;
}
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
//
// Ths pseudo random number generator.
//
uint8_t Rand()
{
Seed = RotateRight(Seed, 3);
Seed += Magic;

return Seed;
}
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
//
// Seed the random number generator.
//
void Srand(uint8_t val)
{
Seed = val;
}
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
//
// This is for testing. Define SETUP to find tha correct magic number
// to hard-code.
//

#define TESTING

#ifdef TESTING

#define NoSETUP

int main()
{
int i;
#ifdef SETUP
for(;;)
{
Seed = 0;
printf("%02x\n", Magic);
i = 0;
while(Rand())
i++;
if(i < 0xfe)
Magic++;
else
break;
}
#else
for(i=0; i< 0xff; i++)
printf("%02x\n", Rand());

#endif

return 0;

}

#endif
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

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