time echo 'n=70332;m=(n+1)/2;a=0;b=1;i=0;while(m>0){z=0;if(m%2)z=2-(m%4);m=(m-z)/2;e[i++]=z};while(i--){c=a*a;a=c+2*a*b;b=c+b*b;if(e[i]>0){t=a;a+=b;b=t};if(e[i]<0){t=a;a=b;b=t-b}};if(n%2)a*a+b*b;if(!n%2)a*(a+2*b)' | bc
14764850684189816403580140143363762977190377750284997600081715975272\ ... 86184952971938819341683867271994735126240287405611087016153703798851\ 46303000784 real 0m0.148s user 0m0.128s sys 0m0.004s
EDIT: Trolling crap removed ;)
takes approx 6 secs on a Core 2 Duo @ 2GHz, and 15 secs on atom based netbooks!
uses monoid (a,b).(x,y)=(ax+bx+ay,ax+by) with identity (0,1), and recursion relations:
F(2n-1)=Fn*Fn+F(n-1)*F(n-1)
F(2n)=(Fn+2*F(n-1))*Fn
then apply fast exponentiation to (1,0)^n = (Fn,F(n-1))
.
Note that: (1,0)^-1=(1,-1) so (a,b).(1,0) = (a+b,a) and (a,b)/(1,0)=(a,b).(1,0)^-1=(b,a-b)
So we can also use a NAF representation to do the exponentiation,http://en.wikipedia.org/wiki/Non-adjacent_form , it's also very fast (about the same, depends on n):
time echo 'n=1000000;m=(n+1)/2;a=0;b=1;i=0;while(m>0){z=0;if(m%2)z=2-(m%4);m=(m-z)/2;e[i++]=z};while(i--){c=a*a;a=c+2*a*b;b=c+b*b;if(e[i]>0){t=a;a+=b;b=t};if(e[i]<0){t=a;a=b;b=t-b}};if(n%2)a*a+b*b;if(!n%2)a*(a+2*b)' | bc
Show Sample Output
Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?
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n=1000000; time bc <<< 'n='$n';m=(n-1)/2;a=1;b=1;d=0;w=a;x=b;y=b;z=d;while(1){if(m%2){s=w*b+x*d;t=y*b+z*d;w=w*a+x*b;if(!--m)break;x=s;y=y*a+z*b;z=t};f=a+d;g=b*b;a=a*a+g;b*=f;d=g+d*d;m/=2};if(n%2)s*s+t*t;if(!n%2)(t+w)*s;'
is faster