Question weather

JTP
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18 Apr 2018 21:59 #7951 by JTP

weather was created by JTP

Trying to give the weather more variety:

Code:

    case 22:
      weather_info.sunlight = SUN_DARK;
      if (rand_number(0, 1) < 1) {
      send_to_outdoor("The night has begun.\r\n");
      } else {
      send_to_outdoor("The night has begun, ......\r\n");
      }
      break;

but i seem to keep getting the else message every time ?

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krell
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19 Apr 2018 13:39 - 19 Apr 2018 13:43 #7952 by krell

Replied by krell on topic weather

rand_number() in utils.c ends with the following line

Code:

return ((circle_random() % (to - from + 1)) + from);

Modulo returns the remainder of division. If you're dividing by zero you're going to get an error, are you not? It would seem intuitive that the remainder of dividing any number by zero would be zero, except for that whole error thing. Perhaps this is why you always end up with the 'else' option, because the system can't calculate the first?

Perhaps a real programmer can comment.

Last edit: 19 Apr 2018 13:43 by krell.

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JTP
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19 Apr 2018 17:19 #7953 by JTP

Replied by JTP on topic weather

Just tried 1, 2 and <2

Now i keep getting the first message instead.

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JTP
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19 Apr 2018 17:20 #7954 by JTP

Replied by JTP on topic weather

So might be a bracket problem, i never Can Seem to get em right.

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krell
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19 Apr 2018 17:55 - 19 Apr 2018 18:05 #7955 by krell

Replied by krell on topic weather

Actually, my original answer was a bit off too. I mixed up "to" and "from". Still, you're doing Modulo, so you have to consider the remainder right? If the Modulo of circle_random() is less than one or two, depending on your condition, then it'll be the first statement executed, otherwise the second statement. I think Modulo is usually performed in integer maths too, IIRC. I don't if any of this helps.

Last edit: 19 Apr 2018 18:05 by krell.

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krell
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19 Apr 2018 19:26 #7956 by krell

Replied by krell on topic weather

random.c holds circle_random()

Code:

#define	m  (unsigned long)2147483647
#define	q  (unsigned long)127773

#define	a (unsigned int)16807
#define	r (unsigned int)2836

/* F(z)	= (az)%m
**	= az-m(az/m)
**
** F(z)  = G(z)+mT(z)
** G(z)  = a(z%q)- r(z/q)
** T(z)  = (z/q) - (az/m)
**
** F(z)  = a(z%q)- rz/q+ m((z/q) - a(z/m))
** 	 = a(z%q)- rz/q+ m(z/q) - az */

static unsigned long seed;

void circle_srandom(unsigned long initial_seed)
{
    seed = initial_seed;
}

unsigned long circle_random(void)
{
   int lo, hi, test;

    hi   = seed/q;
    lo   = seed%q;

    test = a*lo - r*hi;

    if (test > 0)
	seed = test;
    else
	seed = test+ m;

    return (seed);
}

So circle_random() could possibly return 2147483647 as a value. If we use 0 and 1 then you're finding 2147483647 % 2 = 1. If we use 1 and 2 then you're finding 2147483647 % 3 = 1.

Maybe there's a different randomizer in the code you could try?

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