; Lunar Lander game in N8A for n808 VM
; On each turn, the following parameters are displayed in this order:
; altitude (meters), speed (m/s) and remaining fuel (kg)
; Your goal is to apply (or not apply) thrust
; (values that make any sense are 0 to 2000) every 10 seconds of flight
; and get the lunar module to land safely without running out of fuel.
; At the end, the game shows one of the following statuses:
; 4444 is a disaster landing with no survivors,
; 5555 is a crash landing with the crew surviving the impact,
; 6666 is a hard landing with some damage to the pod,
; 7777 is a good landing,
; 8888 is a perfect landing.
; Created by Luxferre in 2025, released into public domain

; constant/variable area

#30 code_dis         ; disaster code
#31 code_crsh        ; crash landing code
#32 code_dmg         ; damage landing code
#33 code_good        ; good landing code
#34 code_perf        ; perfect landing code
#36 crit_crsh        ; criterion for crash landing
#37 crit_dmg         ; criterion for damage landing
#38 crit_good        ; criterion for good landing
#39 crit_perf        ; criterion for perfect landing
#40 alt              ; module altitude
#41 speed            ; module fall speed (m/s)
#42 fuel             ; fuel (in kg)
#52 athr             ; altitude threshold AND time period
#53 ffsd             ; freefall speed delta
#54 capw             ; capsule weight (in kg)
#55 burnrate         ; fuel burn rate
#56 exvel            ; exhaust velocity
#57 c100             ; constant 100
#1 buf               ; buffer variable
#2 floss             ; fuel loss value
#3 m0                ; m0 variable in the equation
#4 m1                ; m1 variable in the equation

; memory initialization part

; zero out the memory (first 57 cells)
dca 57 1             ; set the counter to 57
:clp ica 0 1         ; assign 0 to the cell from the counter
dec 1
jgt 1 :clp

; set constants and initial variable values

dca 10 @athr         ; altitude threshold / time period
dca 25 @ffsd         ; set 16.25 as freefall speed delta
set 0 16 @ffsd
set 74 80 @capw      ; set 7480 as capsule weight
dca 45 @burnrate     ; set 3.45 as fuel burn rate
set 0 3 @burnrate
set 29 0 @exvel      ; set 2900 as exhaust velocity
set 19 30 @alt       ; set 1930 as starting altitude
dca 100 @c100        ; set constant 100
mul @c100 @alt       ; multiply this altitude value by 100
set 16 9 @speed      ; set 1609 as starting speed
set 72 60 @fuel      ; set 7260 as fuel
set 44 44 @code_dis  ; set 4444 as disaster code
set 55 55 @code_crsh ; set 5555 as crash landing code
set 66 66 @code_dmg  ; set 6666 as damage landing code
set 77 77 @code_good ; set 7777 as good landing code
set 88 88 @code_perf ; set 8888 as perfect landing code
dca 67 @crit_crsh    ; set 26.67 as the criterion for crash landing
set 0 26 @crit_crsh
dca 73 @crit_dmg     ; set 9.73 as the criterion for damage landing
set 0 9 @crit_dmg
dca 45 @crit_good    ; set 4.45 as the criterion for good landing
set 0 4 @crit_good
dca 45 @crit_perf    ; set 0.45 as the criterion for perfect landing
set 0 0 @crit_perf

; main action/logic part

:lp out @alt @fuel   ; loop start; print altitude, speed and fuel
dca 0 @floss         ; set fuel loss to 0
jle @fuel :cnt       ; skip prompting for thrust if already out of fuel
inp @floss @floss    ; prompt for thrust into the fuel loss location
mul @burnrate @floss ; multiply thrust by fuel burn rate to get fuel loss
:cnt dva @fuel @m0   ; copy fuel weight into m0
add @capw @m0        ; add capsule weight and fuel weight to get m0
dva @floss @m1       ; prepare m1
sub @m0 @m1          ; m0 - floss => m1
div @m0 @m1          ; m0 / m1 => m1
log @m1 @buf         ; ln (m0 / (m0 - floss)) => buf
mul @exvel @buf      ; multiply the result by the exhaust velocity to get thrust speed delta
sub @speed @buf      ; subtract the thrust speed delta from the current speed
add @ffsd @buf       ; add the freefall speed delta to the current speed
dva @buf @speed      ; copy the resulting speed value back to the holding variable
mul @athr @buf       ; multiply speed by time period into the buffer variable
sub @alt @buf        ; decrease the altitude by the result of this operation
dva @buf @alt        ; restore the altitude variable
sub @fuel @floss     ; decrease the amount of fuel by the fuel loss value
dva @floss @fuel     ; restore the fuel variable
jgt @fuel :flc       ; skip the next instruction if the amount of fuel is positive
dca 0 @fuel          ; just set the amount of fuel to zero if it's negative
:flc jgt @alt :al    ; do the same for altitude
dca 0 @alt           ; set it to zero if negative
:al dva @athr @buf   ; copy altitude threshold to the buffer
sub @alt @buf        ; subtract the threshold from the altitude
jgt @buf :lp         ; go to the loop start if the altitude is above the threshold

; game finalization/scoring part

out @alt @fuel                ; print the final altitude/speed/fuel
dva @crit_perf @buf           ; buffer the perfect speed
sub @speed @buf               ; subtract the perfect speed
jgt @buf :good                ; skip if > 0
out @code_perf @code_perf     ; output the perfect score
juc :end                      ; go to end
:good dva @crit_good @buf     ; buffer the good speed
sub @speed @buf               ; subtract the good speed
jgt @buf :dmg                 ; skip if > 0
out @code_good @code_good     ; output the good score
juc :end                      ; go to end
:dmg dva @crit_dmg @buf       ; buffer the damage speed
sub @speed @buf               ; subtract the damage speed
jgt @buf :crsh                ; skip if > 0
out @code_dmg @code_dmg       ; output the damage score
juc :end                      ; go to end
:crsh dva @crit_crsh @buf     ; buffer the crash speed
sub @speed @buf               ; subtract the crash speed
jgt @buf :disa                ; skip if > 0
out @code_crsh @code_crsh     ; output the crash score
juc :end                      ; go to end
:disa out @code_dis @code_dis ; output the disaster score
:end nnn                      ; program end label