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Random Number between a range?

 
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Chantry



Joined: 18 Jan 2011
Posts: 13

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Random Number between a range?
PostPosted: Mon Feb 07, 2011 6:37 pm     Reply with quote
Hi,

I found this code:
Code:
char random_byte;

char rand(void)   {
   char sum;
   
   sum = 0;
   
   // This calculates parity on the selected bits (mask = 0xb4).
   if(random_byte & 0x80)
      sum = 1;
   
   if(random_byte & 0x20)
      sum ^= 1;
   
   if(random_byte & 0x10)
      sum ^= 1;
   
   if(random_byte & 0x04)
      sum ^= 1;
   
   random_byte <<= 1;
   
   random_byte |= sum;
   
   return(random_byte);
}

void srand(char seed) {
   random_byte = seed;
}


I want wondering if it is possible to generate a number between a specific range? Say for example, I want a random number between 0-20, is this possible, or do I have to keep generating random numbers until I find one which is in range?

Regards,

James
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Mon Feb 07, 2011 8:30 pm     Reply with quote
That function was posted in the early years of the compiler, before CCS
added the standard rand() function. You don't need to use it now.

You can generate random numbers with the rand() function, and set the
maximum value generated by defining the RAND_MAX value.
Read these threads:
http://www.ccsinfo.com/forum/viewtopic.php?t=28834
http://www.ccsinfo.com/forum/viewtopic.php?t=42025

To change RAND_MAX to a different value while the program is running,
see this thread:
http://www.ccsinfo.com/forum/viewtopic.php?t=43069
Chantry



Joined: 18 Jan 2011
Posts: 13

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PostPosted: Tue Feb 08, 2011 5:24 am     Reply with quote
Thank you very much, I did search but couldn't find those mentioned threads.
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