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# gauss.c

```/*
*  methods/gauss.c
*
*  Calculate the sum of a given range of integer numbers.
*
*  Somewhat of a more subtle way of calculation - and it even has a story
*  behind it:
*
*  Supposedly during math classes in elementary school, the teacher of
*  young mathematician Gauss gave the class an assignment to calculate the
*  sum of all natural numbers between 1 and 100, hoping that this task would
*  keep the kids occupied for some time. The story goes that Gauss had the
*  result ready after only a few minutes. What he had written on his black
*  board was something like this:
*
*    1 + 100 = 101
*    2 + 99  = 101
*    3 + 98  = 101
*    .
*    .
*    100 + 1 = 101
*
*    s = (1/2) * 100 * 101 = 5050
*
*  A more general form of this formula would be
*
*    s = (1/2) * (max + min) * (max - min + 1)
*
*  which is used in the piece of code below to implement the requested
*  function in constant time, i.e. without dependencies on the size of the
*  input parameters.
*
*/

#include "gauss.h"

int gauss_get_sum (int min, int max)
{
/* This algorithm doesn't work well with invalid range specifications
so we're intercepting them here. */
if (max < min)
{
return 0;
}

return (int) ((max + min) * (double) (max - min + 1) / 2);
}
```

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