;redcode
;name Prime, bonus and big bucks
;author Pierre Baillargeon
;strategy Load this program at address 500 to make the result fall in
;strategy the range 7999-7900.
;strategy The base idea is to use negative numbers. We can thus take
;strategy advantage of all the decrease side-effects of MARS-88. The
;strategy second idea is the technique to store base-prime in the
;strategy B-field of the code. We can therefore calculate the prime-
;strategy factor at the beginning with very few instructions.
;strategy
;strategy We use a small substract loop to calculate the division.
;strategy If the result of the substract loop is zero, we have found a
;strategy factor, so keep it and re-use it again.
;strategy
;strategy If the result is non-zero, scan the marked memory, beginning
;strategy at the current prime-factor to find the new prime-factor.
;strategy
;strategy Now that I've seen some others, I understand that my downfall
;strategy is the LOOOONG time it takes to compute division of small
;strategy primes (2 takes 4000 loops !).
;strategy
bottom equ next ; last instruction
top equ base
pprime equ top-1 ; used to erathostene-out prime numbers
result equ top-500 ; where we save factors
number equ bottom+1 ; where the number will be stored as a negative
test equ bottom+2 ; number is temporary stored during calculation
base mov #5,0 ; init the loop count
primes mov @base,pprime ; (-2) mark the location as non-prime
prime add @base,pprime ; (-3) move back by the amount of base-prime
mov #-1,@pprime ; (-4) tag number as non-prime
cmp #-420,pprime ; (-5) stop at 420 (3 x 4 x 5 x 7)
jmp prime,-7 ; (-7) redo mark loop
djn primes,base ; do all the base-prime
mov #-2,pprime ; begin dividing with first factor: 2
sub #0381,number ; *** place the nymber in the A-field ***
calc mov number,test ; get number ready for test
CPU jmz found,test ; if zero, found factor
sub pprime,test ; substract current divisor
slt pprime,test ; test < pprime -> new divisor
djn CPU,@quot ; increase quotient
new_div jmn new_div,