Date: Sun, 11 Nov 2001 23:40:09 +0200 From: devotee <sixthfish@gmx.net> To: freebsd-test@freebsd.org Subject: strange rand() behaviuor Message-ID: <20011111234009.A2197@berloga.volodya.artm.org>
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Hi, list !
My old RSA-code failed to work in proper maner under FreeBSD 4.4. I spent 2 hours, and it seems FreeBSD version of rand() or libc or gcc or whatever have some bugs in it. Here's sample code:
#include <stdio.h>
int main ()
{
int i,j;
for (i=0; i<256*10; i++) {
j = rand();
if (!(i%256)) printf ("i=%5d j=0x%08X j%%256=0x%02X\n",i,j,j%256);
}
return 0;
}
It just prints each 256th random number from rand();
Here's my output:
bash-2.05$ gcc randtest.c -o randtest
bash-2.05$ ./randtest
i= 0 j=0x41C67EA6 j%256=0xA6
i= 256 j=0x32AA09A6 j%256=0xA6
i= 512 j=0x559994A6 j%256=0xA6
i= 768 j=0x5A951FA6 j%256=0xA6
i= 1024 j=0x719CAAA6 j%256=0xA6
i= 1280 j=0x4AB035A6 j%256=0xA6
i= 1536 j=0x15CFC0A6 j%256=0xA6
i= 1792 j=0x02FB4BA6 j%256=0xA6
i= 2048 j=0x4232D6A6 j%256=0xA6
i= 2304 j=0x037661A6 j%256=0xA6
As you can see, last octet of each rand value is the same !!!
Under debian linux same code outputs:
devotee@nerve:~$ gcc randtest.c -o randtest
devotee@nerve:~$ ./randtest
i= 0 j=0x6B8B4567 j%256=0x67
i= 256 j=0x5D888A08 j%256=0x08
i= 512 j=0x4695AE95 j%256=0x95
i= 768 j=0x2C06DCF3 j%256=0xF3
i= 1024 j=0x170EB52B j%256=0x2B
i= 1280 j=0x22317590 j%256=0x90
i= 1536 j=0x1E1C83A1 j%256=0xA1
i= 1792 j=0x3F754C7B j%256=0x7B
i= 2048 j=0x10A93FB7 j%256=0xB7
i= 2304 j=0x12130ECA j%256=0xCA
(that's what i expected to see under freebsd)
What's wrong ???
--
devotee, http://volodya.artm.org
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