random-length.c

   1 #include <stdlib.h>
   2
   3 #include "arch.h"       // page_size
   4 #include "sanitise.h"
   5 #include "random.h"
   6
   7 unsigned long get_len(void)
   8 {
   9         int i = 0;
  10
  11         i = rand32();
  12
  13         /* short circuit if 0 */
  14         if (i == 0)
  15                 return 0;
  16
  17         switch (rand() % 6) {
  18
  19         case 0: i &= 0xff;
  20                 break;
  21         case 1: i &= page_size;
  22                 break;
  23         case 2: i &= 0xffff;
  24                 break;
  25         case 3: i &= 0xffffff;
  26                 break;
  27         case 4: i &= 0xffffffff;
  28                 break;
  29         default:
  30                 // Pass through
  31                 break;
  32         }
  33
  34         /* again, short circuit if 0 */
  35         if (i == 0)
  36                 return 0;
  37
  38         /* we might get lucky if something is counting ints/longs etc. */
  39         if (rand() % 100 < 25) {
  40                 int _div = 1 << ((rand() % 4) + 1);      /* 2,4,8 or 16 */
  41                 i /= _div;
  42         }
  43
  44         return i;
  45 }