| lostcauz |
Dec 12th, 2004 3:59 PM |
If n is even divide by 2, if odd multiply 3 add 1.
Testing for longest chain less than one million.
Any suggestions to speed it up? 4.0504s on 233/128
:
xor edi, edi ; zero -longest chain
xor esi, esi ; zero -inner loop counter
mov ecx, 1000000 ; set main loop counter
mov edx, ecx ; copy to edx
begin:
mov eax, edx ; prepare for even/odd test
and eax, 1 ; test even/odd number
jz inner ; if zero number is even
lea eax, [edx*2+edx+1] ; number is odd perform 3n+1
mov edx, eax ; load result back to edx
inner:
shr edx, 1 ; numbers are all even now so div by 2
inc esi ; increment present number chain
cmp edx, 1 ; if number is 1 we are done with it
jne begin ; continue chain
cmp esi, edi ; if chain > longest_chain
jb outer ; no, goto outer
mov edi, esi ; yes, update longest_chain
mov ebx, ecx ; save number having longest chain
outer:
xor esi, esi ; reset inner loop counter
dec ecx ; decrement outer loop counter
mov edx, ecx ; save as next number to iterate
jnz begin ; if outer loop counter > 0 continue
mov eax, ebx ; return final result
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