home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Power-Programmierung
/
CD1.mdf
/
magazine
/
pctchnqs
/
1990
/
number4
/
l1.asm
< prev
next >
Wrap
Assembly Source File
|
1990-07-29
|
3KB
|
100 lines
; *** Listing 1 ***
;
; Program to illustrate searching through a buffer of a specified
; length until either a specified byte or a zero byte is encountered.
; A standard loop terminated with LOOP is used.
.model small
.stack 100h
.data
; Sample string to search through.
SampleString label byte
db 'This is a sample string of a long enough length '
db 'so that raw searching speed can outweigh any '
db 'extra set-up time that may be required.',0
SAMPLE_STRING_LENGTH equ $-SampleString
; User prompt.
Prompt db 'Enter character to search for:$'
; Result status messages.
ByteFoundMsg db 0dh,0ah
db 'Specified byte found.',0dh,0ah,'$'
ZeroByteFoundMsg db 0dh,0ah
db 'Zero byte encountered.',0dh,0ah,'$'
NoByteFoundMsg db 0dh,0ah
db 'Buffer exhausted with no match.',0dh,0ah,'$'
.code
Start proc near
mov ax,@data ;point to standard data segment
mov ds,ax
mov dx,offset Prompt
mov ah,9 ;DOS print string function
int 21h ;prompt the user
mov ah,1 ;DOS get key function
int 21h ;get the key to search for
mov ah,al ;put character to search for in AH
mov cx,SAMPLE_STRING_LENGTH ;# of bytes to search
mov si,offset SampleString ;point to buffer to search
call SearchMaxLength ;search the buffer
mov dx,offset ByteFoundMsg ;assume we found the byte
jc PrintStatus ;we did find the byte
;we didn't find the byte, figure out
; whether we found a zero byte or
; ran out of buffer
mov dx,offset NoByteFoundMsg
;assume we didn't find a zero byte
jcxz PrintStatus ;we didn't find a zero byte
mov dx,offset ZeroBytefoundMsg ;we found a zero byte
PrintStatus:
mov ah,9 ;DOS print string function
int 21h ;report status
mov ah,4ch ;return to DOS
int 21h
Start endp
; Function to search a buffer of a specified length until either a
; specified byte or a zero byte is encountered.
;
; Input:
; AH = character to search for
; CX = maximum length to be searched (must be > 0)
; DS:SI = pointer to buffer to be searched
;
; Output:
; CX = 0 if and only if we ran out of bytes without finding
; either the desired byte or a zero byte
; DS:SI = pointer to searched-for byte if found, otherwise byte
; after zero byte if found, otherwise byte after last
; byte checked if neither searched-for byte nor zero
; byte is found
; Carry Flag = set if searched-for byte found, reset otherwise
SearchMaxLength proc near
cld
SearchMaxLengthLoop:
lodsb ;get the next byte
cmp al,ah ;is this the byte we want?
jz ByteFound ;yes, we're done with success
and al,al ;is this the terminating 0 byte?
jz ByteNotFound ;yes, we're done with failure
loop SearchMaxLengthLoop ;it's neither, so check the next
; byte, if any
ByteNotFound:
clc ;return "not found" status
ret
ByteFound:
dec si ;point back to the location at which
; we found the searched-for byte
stc ;return "found" status
ret
SearchMaxLength endp
end Start