Comment On Seriously, I'm A Genius

Here's a WTF:
int aFractionPortion = rand();
double aValue = (double)anIntegerPortion + 1.0/(double)aFractionPortion;
From the documentation for rand():

"The rand function returns a pseudorandom integer in the range 0 to RAND_MAX." 

But it will only cause the occasional warp core breech, since rand doesn't return zero all that often.

Mike R:

And on a more serious note:



Where does this "genius" get off  calling this thing a random number generator,



This whole train-wreck of a function could be summed as follows:



return rand()*(iMax-iMin)+iMin

1. Never seen a form of 'hungarian' notation using the/a/an before.


2. If theMin == theMax, shouldn't you return theMin by definition?
3. It
   would be convienent if GenerateRandomValue(1, 10) was equivalent to
   GenerateRandomValue(10, 1) (minor, but technically they mean the same).


4. rand() returns a number from 0 to 32767, so there is a potentialy divide by zero error (assuming this is C++).
   
   


5. The fractional portion of the generated 'random' number will not
   be equally distributed (there will be many more values closer to 0.0
   than 1.0). For instance with a non-fractional range (say 1.0 to 10.0)
   its impossible to get a random number ending in 0.51 to 0.99.


6. You can only end up getting numbers from theMin to theMin+32768. If you wanted to do a GenerateRandomValue(1, 1e6), well, you're just outta luck.


7. I'm afraid I don't see how it can be an infinite loop...a true 'genuis' would know about fmod() or know how to write one.


8. Love some of the comments, like for the range calculation (ohh, so that's how you compute a range from a max/min).

JimNtexas:

Here's a WTF:
int aFractionPortion = rand();
double aValue = (double)anIntegerPortion + 1.0/(double)aFractionPortion;

-- 

Henryk Plötz

Grüße aus Berlin

Anonymous:

RE: Infinite loop



What happens in the for loop if theMin==theMax? :)

Anonymous:

i don't see the infinite loop.  Anyone want to fill me in?

Anonymous:

Anonymous:

RE: Infinite loop



What happens in the for loop if theMin==theMax? :)

Then the function returns 0.0.  Read the first five lines of the WTFunction :).

Anonymous:

RE: Infinite loop



What happens in the for loop if theMin==theMax? :)

Alex Papadimoulis:

double MUTils::GenerateRandomValue(double theMin, double theMax)

{

  if (theMin >= theMax) {

    // error in parameters, so return 0.0

    return 0.0;

  }

Anonymous:

>infinite loop

doubles are not real numbers - they are approximations. the math that happens with them is therefore imperfect as well.

Anonymous:

RE: Infinite loop



What happens in the for loop if theMin==theMax? :)

Anonymous:

Floating point arithmetic is imprecise.  If
you add two numbers of greatly differing magnitude, the smaller number
will not have an effect.  For example, 1e10 + 0.001 == 1e10. 
So if aRange was much smaller than aValue, aValue would never change.

CornedBee:

Indeed, depending on the FPU setup this might go into an infinite loop
instead of crashing if the second rand() call returns zero.

munificent:

I've never written an RNG myself, but I can't imagine you could do a decent one in just a few lines of code.

John Smallberries:

At least no controvery like yeseterday.


I think we all can agree this is WTFery of the highest caliber.

md2perpe:

John Smallberries:

At least no controvery like yeseterday.


I think we all can agree this is WTFery of the highest caliber.

I think so too. I agree that she's not the "Genius" she thinks she is.
She merely seems to be an average programmer, doing most things right,
failing (getting a blackout?) now-and-then. Most WTF postings here are
definitely true WTF:s, making you ask: "How could he/she even get the
idea of doing that?"

Anonymous:

Anonymous:

RE: Infinite loop



What happens in the for loop if theMin==theMax? :)

Then the function returns 0.0.  Read the first five lines of the WTFunction :).

Sean:

At least it's pretty well-commented.

Anonymous:

In addition to the infinite loops mentioned, there may also be a
possibility of infinite loop due to *very large range*, as
aValue-=aRange may wrap around to some really large number and you are
back to the start.  I've stupidly done this myself with
off-by-one-errors and integers...wondering why the loop spins and spins
on while (i >= MIN_INT_VALUE) :)  (this was in Java though, but
the same idea applies)

  // make the double be between 0 and aRange
  for (; aRange <= aValue; aValue -= aRange);

It seems to me that anytime the range is mostly negative, the routine will enter an endless loop condition.

Example: theMin := -15  theMax:=0

Also, it might just SEEM like an endless loop if theMin is a very large number, such as 3.1E31

(this is my first WTF post -- thanks to Dennis Sherman for telling me about this site)

 > year or so after she left

Women and Computer Science don't mix! ;-)

chb:

The naming of the variables kills me.

(a|an|the|its)



Maybe she's a "hungarian notation fundamentalist" *ducks*

Mike R:

Mike R:

And on a more serious note:

Where does this "genius" get off  calling this thing a random number generator,

This whole train-wreck of a function could be summed as follows:

return rand()*(iMax-iMin)+iMin

[:$] Heh.. replace rand with (float(rand())/float(RAND_MAX))

Thank you, I don't know why people are so terrified of a using little arithmetic now and then.