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From:	ld AT jasmine DOT netrix DOT com (Long Doan)
Subject:	Re: Scrolling in ASM
Lines:	33
Sender:	news AT netrix DOT com
Organization:	Netrix Corporation
Date:	Wed, 1 Nov 1995 22:27:38 GMT
To:	djgpp AT sun DOT soe DOT clarkson DOT edu
Dj-Gateway:	from newsgroup comp.os.msdos.djgpp

[The original message was about getting SegFault when copying 199
 bytes of Video Ram to another part in Video Ram.]

Since the copy operation copies 199 bytes, it's possible that the code
use some thing like:
   push eax, ecx, esi, edi, ds, and es
   movl $199, %ecx
   movl $source, %esi
   movl $dest, %edi
   movw _vid_ram_sel, %ax
   movw %ax, %ds
   movw %ax, %es
   rep
   movsb
   pop registers.

Which can cause trouble if:
1. Instead of using 199 and movsb, 199/4 and movsl is used, so the
   last byte is out of the segment.
2. %es and/or %ds is not restored, and causes crashes later on.
3. %esi and/or %edi is not restored, and causes crashes later on.

It will be more helpful if you can post the code that causes trouble.

Hope that helps,
Long.
-- 
==============================================================
Long Doan                                        ld AT netrix DOT com     
Netrix Corporation                         ldoan1 AT osf1 DOT gmu DOT edu
13595 Dulles Technology Drive                               
Herndon Va 22071
==============================================================

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