coderloop: src/collatz.f annotate

initial committ

rev	line source
rlm@0	1 program collatz
rlm@0	2 implicit none
rlm@0	3 character (len = 100) :: file_name
rlm@0	4 integer, parameter :: big = selected_int_kind(11)
rlm@0	5 integer :: n
rlm@0	6 call getarg( 1, file_name )
rlm@0	7 OPEN(unit = 7, file = file_name)
rlm@0	8 read (7,*) n
rlm@0	9 write (unit = *, fmt = "(I0)") search_collatz(n)
rlm@0	10
rlm@0	11 contains
rlm@0	12
rlm@0	13 function collatz_next (n) result (r)
rlm@0	14 implicit none
rlm@0	15 integer (kind = big) :: r,n
rlm@0	16 if (0 == mod(n,2)) then
rlm@0	17 r = n/2
rlm@0	18 else
rlm@0	19 r = 1 + 3*n
rlm@0	20 end if
rlm@0	21 end function collatz_next
rlm@0	22
rlm@0	23 function collatz_length (n) result (r)
rlm@0	24 implicit none
rlm@0	25 integer (kind = big) :: t
rlm@0	26 integer :: n,r
rlm@0	27 r = 1
rlm@0	28 t = n
rlm@0	29 do
rlm@0	30 if (1 == t) then
rlm@0	31 exit
rlm@0	32 end if
rlm@0	33 r = r + 1
rlm@0	34 t = collatz_next(t)
rlm@0	35 end do
rlm@0	36 end function collatz_length
rlm@0	37
rlm@0	38 function search_collatz (n) result (r)
rlm@0	39 implicit none
rlm@0	40 integer n,r,i,max,max_val,temp_val
rlm@0	41 integer (kind = big) :: t
rlm@0	42 t = n
rlm@0	43 do i = 1,n-1
rlm@0	44 temp_val = collatz_length(i)
rlm@0	45 if (temp_val > max_val) then
rlm@0	46 max = i
rlm@0	47 max_val = temp_val
rlm@0	48 end if
rlm@0	49 end do
rlm@0	50 r = max
rlm@0	51 end function search_collatz
rlm@0	52 end program collatz

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