XPost: comp.os.msdos.programmer, alt.lang.asm
From: admin@nospicedham.127.0.0.1
On Wed, 25 Jan 2023 15:03:26 +0100
Terje Mathisen wrote:
> Kerr-Mudd, John wrote:
> > Finally, a rot13 program for DOS that's smaller than the standard version
> > with jumps:
> >
> >
> > ->u 100 l2E
> > 1637:0100 B6 02 mov dh,02
dirty save of 1 byte by not fully specifying the IOAREA
> > 1637:0102 B4 3F mov ah,3F
> > 1637:0104 89 C1 mov cx,ax
dirty save of 1 byte by not fully specifying the IOAREA_Lth
> > 1637:0106 CD 21 int 21
> > 1637:0108 89 D6 mov si,dx
> > 1637:010A 91 xchg ax,cx
> > 1637:010B E3 20 jcxzw 012D
> > 1637:010D 51 push cx
>
> The loop starts here of course!
>
> > 1637:010E AC lodsb
> > ; main rot13 rtn
> > 1637:010F 24 DF and al,DF
> Folding to lowercase ascii
> > 1637:0111 2C 41 sub al,41
> > 1637:0113 3C 1A cmp al,1A
> Checking that it was in-range
> > 1637:0115 18 E4 sbb ah,ah
> > 1637:0117 3C 0D cmp al,0D
>
> Very nice, handling plus/minus for upper and lower case!
>
> > 1637:0119 D6 salc
> > 1637:011A 25 1A F3 and ax,F31A
> > 1637:011D 00 E0 add al,ah
> > 1637:011F 00 44 FF add [si-01],al
> >
> > 1637:0122 E2 EA loopw 010E
> > 1637:0124 59 pop cx
> > 1637:0125 43 inc bx
> > 1637:0126 B4 40 mov ah,40
> > 1637:0128 CD 21 int 21
> > 1637:012A 4B dec bx
> > 1637:012B EB D5 jmp 0102
> > 1637:012D C3 ret
> > -> d 100 l2E
> > 1637:0100 B6 02 B4 3F-89 C1 CD 21-89 D6 91 E3-20 51 AC 24 ...?...!.... Q.$
> > 1637:0110 DF 2C 41 3C-1A 18 E4 3C-0D D6 25 1A-F3 00 E0 00 .,A<...<..%.....
> > 1637:0120 44 FF-E2 EA 59 43-B4 40 CD 21-4B EB D5 C3 D...YC.@.!K...
> > -> q
> >
>
TYVM, It's appreciated, especially from you.
simpler? version; hardcoded IOAREA, rotamt in dl
->u 100 l2E
1637:0100 BA 0D 1A mov dx,1A0D
1637:0103 B4 3F mov ah,3F
1637:0105 89 C1 mov cx,ax
1637:0107 CD 21 int 21
1637:0109 89 D6 mov si,dx
1637:010B 91 xchg ax,cx
1637:010C E3 1F jcxzw 012D
1637:010E 51 push cx
1637:010F AC lodsb
1637:0110 24 DF and al,DF
1637:0112 2C 41 sub al,41
1637:0114 38 D0 cmp al,dl
1637:0116 18 E4 sbb ah,ah
1637:0118 38 F0 cmp al,dh
1637:011A D6 salc
1637:011B 21 D0 and ax,dx
1637:011D 28 C4 sub ah,al
1637:011F 00 64 FF add [si-01],ah
1637:0122 E2 EB loopw 010F
1637:0124 59 pop cx
1637:0125 43 inc bx
1637:0126 B4 40 mov ah,40
1637:0128 CD 21 int 21
1637:012A 4B dec bx
1637:012B EB D6 jmp 0103
1637:012D C3 ret
-> d 100 l2E
1637:0100 BA 0D 1A B4-3F 89 C1 CD-21 89 D6 91-E3 1F 51 AC ....?...!.....Q.
1637:0110 24 DF 2C 41-38 D0 18 E4-38 F0 D6 21-D0 28 C4 00 $.,A8...8..!.(..
1637:0120 64 FF E2 EB-59 43 B4 40-CD 21 4B EB-D6 C3 d...YC.@.!K...
-> q
Sad there's no^w little interest in x86 asm these days, but I suppose such
things might have been "hot" 40 years ago.
(Modesty forbids me from adding "me too!")
--
Bah, and indeed Humbug.
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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