[Giagnocavo]Michael::Write() - Help me reduce this program

Friday, February 25, 2005

Help me reduce this program

This is probably gonna be a post where I end up looking like an idiot, but here goes...

I was playing around and wrote a small program to dump the video font table. I started at around 33 bytes, but want to get it as small as possible (to um, learn! :)). Here's what I have so far:

[BITS 16]
[ORG 100h]
[SECTION .text] 
start:
mov al,64   ; Init (but don't clear) video     
INT 10h      ; Need to call int10h to start NT's DOS video emulation I think... 
mov ax,VideoBuffer 
mov es,ax    ; Put video buffer segment into ES
mov ah,007h    ; White text (Attribute 7). AL is already zero from loading the video buffer
mov cl,255    ; All oem chars
charloop:
 stosw 
 inc ax ; Increase char, don't worry about the attribute; it's high
 loop charloop
ret
[SECTION .data] 
VideoBuffer EQU 0B800h

This assembles into:

00000000  B040              mov al,0x40
00000002  CD10              int 0x10
00000004  B800B8            mov ax,0xb800
00000007  8EC0              mov es,ax
00000009  B407              mov ah,0x7
0000000B  B1FF              mov cl,0xff
0000000D  AB                stosw
0000000E  40                inc ax
0000000F  E2FC              loop 0xd
00000011  C3                ret

For a total of 18 bytes. We can save 2 bytes by killing the mov ah,7h, but that's the video attribute, and the value that's in AH is B8, which is light grey on cyan. This looks ugly. We can also remove the first mov al and int10 call, but that means something else has to initialize the video, and that's cheating. (With those two optimizations, we're down to 12 bytes though.)
Anyone experienced want to teach me a lesson? Please? :)

Code

Friday, February 25, 2005 6:05:13 AM UTC

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