Robert Covington wrote:

> I would like to know why the below generator fails in FB...is it 
> because it requires "wide" math, that 64 bit stuff available in C 
> compilers? It seems that the  n = (n<<13) ^ n overflows eventually?
>
> C:
> fn Noise2D(integer x, integer y)
>     n = x + y * 57
>     n = (n<<13) ^ n;
>     return ( 1.0 - ( (n * (n * n * 15731 + 789221) + 1376312589) & 
> 7fffffff) / 1073741824.0);
>   end function


local mode
local fn Noise2D#( x as long, y as long )
'~'1
dim as long  n

n = x + y * 57
n = (n<<13) xor n
n = (n * (n * n * 15731 + 789221) + 1376312589) and 0x7fffffff
end fn = 1.0 - n/1073741824.0


Robert P.