[avr-libc-dev] [bug #18662] rand() keeps returning the same value if seeded with 0

[Roland Bluethgen]

URL:
  <http://savannah.nongnu.org/bugs/?18662>

                 Summary: rand() keeps returning the same value if seeded
with 0
                 Project: AVR C Runtime Library
            Submitted by: calocybe
            Submitted on: Sunday 12/31/2006 at 14:57
                Category: Library
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
        Percent Complete: 0%
             Assigned to: None
        Originator Email: calocybe
             Open/Closed: Open
         Discussion Lock: Any

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Details:

The function do_rand() in rand.c, invoked by rand(), keeps returning the same
value, in particular RAND_MAX, if the static variable 'next' is seeded with
srand(0).

The algorithm in do_rand() calculates a new value for *ctx from the current
value of *ctx.
If *ctx == 0, the new value calculated will be 0x7fffffffL.
If *ctx == 0x7fffffffL, the new value calculated will be 0x7fffffffL again.
Thus, the return value will be always the same.

This does most probably apply to random() in an analogous manner as the code
in do_random() in random.c looks very much the same, only the return value
will be RANDOM_MAX, not RAND_MAX.





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