Possible bug in STD C quicksort. Am i missing something ?

Question

xorshift init: 7731

A: 2064221648 1036493097 633233112 583013546 721278080 -1646392714 -829660162 478401127

E: 583013546 633233112 721278080 10

Answer 1

Compiled with

gcc sort.c -Wall -Wextra

There was one error about not matching conversion specifier (unsigned int requires %u but you had %lld - possibly typo for %11d but even then it were wrong.

Running, I get sometimes correct output, sometimes not. So I compiled with -fsanitize=undefined, and

sort.c:11:13: runtime error: signed integer overflow: 
    1288106901 - -1003011281 cannot be represented in type 'int'
E: 
  290879035
  591885416
  767444883
 1288106901
 1955087149
-1509681722
-1289472872
-1003011281

I.e. your smart code wasn't too smart there. The correct way to return a value from the comparison function would be

return x < y ? -1 : x > y ? 1 : 0;

or

return (x > y) - (x < y);

as suggested by HolyBlackCat