Just how bad is the Microsoft Visual C++ 6 rand function, anyway?

[Werner Koch]

On Tue, 21 May 2002 11:52:01 -0400, Trei, Peter said:

> int __cdecl rand (void)
> {
>         return(((holdrand = holdrand * 214013L + 2531011L) >> 16) & 0x7fff);
> }

Which looks pretty standard and ISO-C compatible as long as RAND_MAX
yields 0x7fff.  Recall that rand() was never intended as a
cryptographic strong RNG - IIRC the specs say that it must produce the
same sequence of number for a given seed (set with srand()).

Ah yes, latest Posix draft:

   The rand () function shall compute a sequence of pseudo-random
   integers in the range 0 to {RAND_MAX} with a period of at least
   232.  The rand( ) function need not be reentrant. A function that
   is not required to be reentrant is not required to be thread-safe.
   The rand_r( ) function shall compute a sequence of pseudo-random
   integers in the range 0 to {RAND_MAX}. (The value of the {RAND_MAX}
   macro shall be at least 32 767.)



  Werner


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