MELT.COM
From SizeCoding
MELT.COM was written by an unknown author in the 1980s. Originally 49 bytes in size, it performs the following cute effect:
The original source is lost to history, but here's a quick commented disassembly:
org 100h
mov ax, 0B800h
mov es, ax ; es now points to screen segment
doScreen:
mov cx, 2000 ; Going to loop over all 2000 characters
; (80 * 25 = 2000)
xor bx, bx ; bx = 0
; bx is also our "num of altered chars" counter
mov di, bx ; es:di now points at the screen (b800:0000)
alterChars:
mov ah, es:[di] ; Retreive onscreen character
cmp ah, 32 ; comp to a space character (#32)
jz short nextChar ; If already a space, do nothing
jl short upToSpace ; If lower than a space, increase upward
dec ah ; If higher than a space, decrease downward
mov es:[di], ah ; Store altered character back to screen
inc bx ; increase "number of processed chars" counter
jmp short nextChar ; Keep processing characters
; ---------------------------------------------------------------------------
upToSpace:
inc ah ; Increase character upwards towards a space
mov es:[di], ah ; Store altered character back to screen
inc bx ; increase "number of processed chars" counter
nextChar:
inc di
inc di ; es:di now points to next character
loop alterChars ; Continue processing characters
cmp bx, 0 ; Were any characters processed?
jnz short doScreen ; If so (bx != 0), keep processing
mov ah, 4Ch ; Otherwise, get ready to terminate
int 21h ; DOS - 2+ - QUIT WITH EXIT CODE (EXIT)
