Re: KISS4691, a potentially top-ranked RNG.

[Ian Collins <ian-news@hotmail.com>]

On 05/ 2/11 03:31 AM, Thad Smith wrote:
>
> Here is a modification of the program with masking to produce correct results
> with any conforming C implementation.  It truncates where when required.  A good
> optimizer should eliminate the unneeded masking for 32-bit unsigned long.

Why oh why can't people just use fixed width types?  What's the 
obsession with unsigned long and masking?

Add

#include <stdint.h>

change all references to "unsigned long" to uint32_t, remove all 
references to M32.

> static unsigned long xs = 521288629;
> static unsigned long xcng = 362436069;
> static unsigned long Q[4691];

> #define M32 0xffffffff
>
> unsigned long   MWC(void)
> {
>       static unsigned long c = 0;
>       static unsigned long j = 4691;
>       unsigned long   t;
>       unsigned long   x;
>       j = (j<  4690) ? j + 1 : 0;
>       x = Q[j];
>       t = ((x<<  13) + c)&  M32;
>       if (t<  c) {
>           c = (x>>  19) + 1;
>           t = (t + x)&  M32;
>       } else {
>           t = (t + x)&  M32;
>           c = (x>>  19) + (t<  x);
>       }
>       return (Q[j] = t);
>
> }
>
> void            initMWC(void)
> {
>       unsigned long   i;
>       for (i = 0; i<  sizeof Q / sizeof Q[0]; i++)
>           Q[i] = ((xcng = 69069 * xcng + 123) + (xs = (xs ^ (xs<<  13))&  M32,
>                   xs ^= (xs>>  17), xs ^= (xs<<  5)))&  M32;
>
> }
>
> #ifdef UNIT_TEST
>
> #include<stdio.h>
>
> int             main()
> {
>       unsigned long   i;
>       unsigned long   x;
>
>       initMWC();
>
>       printf("Does  MWC result=3740121002 ?\n");
>       for (i = 0; i<  1000000000; i++)
>           x = MWC();
>       printf("%27u\n", x);
>
>       printf("Does KISS result=2224631993 ?\n");
>       for (i = 0; i<  1000000000; i++)
>           x = (MWC() + (xcng = 69069 * xcng + 123) + (xs = (xs ^ (xs<<  13))&  M32,
>                xs ^= (xs>>  17), xs ^= (xs<<  5)));
>       printf("%27u\n", x);
>       return 0;
> }
>
> #endif
>
>
>


-- 
Ian Collins