Misc/abrash-black-book
Watch
1
0
Fork
You've already forked abrash-black-book
 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Use backtick code blocks for syntax highlighting

Browse source
This commit is contained in:
James Gregory 2013-12-31 11:38:48 +11:00
commit f658bfbb40
203 changed files with 26546 additions and 25801 deletions
Download patch file Download diff file Expand all files Collapse all files

70
22-01.md
View file

@ -55,40 +55,42 @@ are mine.
**LISTING 22.1 L22-1.ASM**
OnStack struc ;data that's stored on the stack after PUSH BP
OldBP dw ? ;caller's BP
RetAddr dw ? ;return address
Filler dw ? ;character to fill the buffer with
Attrib dw ? ;attribute to fill the buffer with
BufSize dw ? ;number of character/attribute pairs to fill
BufOfs dw ? ;buffer offset
BufSeg dw ? ;buffer segment
EndMrk db ? ;marker for the end of the stack frame
OnStack ends
;
ClearS proc near
push bp ;save caller's BP
mov bp,sp ;point to stack frame
cmp word ptr [bp].BufSeg,0 ;skip the fill if a null
jne Start ; pointer is passed
cmp word ptr [bp].BufOfs,0
je Bye
Start: cld ;make STOSW count up
mov ax,[bp].Attrib ;load AX with attribute parameter
and ax,0ff00h ;prepare for merging with fill char
mov bx,[bp].Filler ;load BX with fill char
and bx,0ffh ;prepare for merging with attribute
or ax,bx ;combine attribute and fill char
mov bx,[bp].BufOfs ;load DI with target buffer offset
mov di,bx
mov bx,[bp].BufSeg ;load ES with target buffer segment
mov es,bx
mov cx,[bp].BufSize ;load CX with buffer size
rep stosw ;fill the buffer
Bye:mov sp,bp ;restore original stack pointer
pop bp ; and caller's BP
ret EndMrk-RetAddr-2 ;return, clearing the parms from the stack
ClearS endp
```nasm
OnStack struc ;data that's stored on the stack after PUSH BP
OldBP dw ? ;caller's BP
RetAddr dw ? ;return address
Filler dw ? ;character to fill the buffer with
Attrib dw ? ;attribute to fill the buffer with
BufSize dw ? ;number of character/attribute pairs to fill
BufOfs dw ? ;buffer offset
BufSeg dw ? ;buffer segment
EndMrk db ? ;marker for the end of the stack frame
OnStack ends
;
ClearS proc near
push bp ;save caller's BP
mov bp,sp ;point to stack frame
cmp word ptr [bp].BufSeg,0 ;skip the fill if a null
jne Start ; pointer is passed
cmp word ptr [bp].BufOfs,0
je Bye
Start: cld ;make STOSW count up
mov ax,[bp].Attrib ;load AX with attribute parameter
and ax,0ff00h ;prepare for merging with fill char
mov bx,[bp].Filler ;load BX with fill char
and bx,0ffh ;prepare for merging with attribute
or ax,bx ;combine attribute and fill char
mov bx,[bp].BufOfs ;load DI with target buffer offset
mov di,bx
mov bx,[bp].BufSeg ;load ES with target buffer segment
mov es,bx
mov cx,[bp].BufSize ;load CX with buffer size
rep stosw ;fill the buffer
Bye:mov sp,bp ;restore original stack pointer
pop bp ; and caller's BP
ret EndMrk-RetAddr-2 ;return, clearing the parms from the stack
ClearS endp
```
The first thing you'll notice about Listing 22.1 is that **ClearS** uses
a **REP STOSW** instruction. That means that we're not going to improve