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<HTML>
<HEAD>
<META name=vsisbn content="1576101746">
<META name=vstitle content="Michael Abrash's Graphics Programming Black Book, Special Edition">
<META name=vsauthor content="Michael Abrash">
<META name=vspublisher content="The Coriolis Group">
<META name=vspubdate content="07/01/97">
<META name=vscategory content="Web and Software Development: Game Development,Web and Software Development: Graphics and Multimedia Development">
<TITLE>Michael Abrash's Graphics Programming Black Book Special Edition: Hints My Readers Gave Me</TITLE>
<!-- HEADER -->
<!-- Empty Reference Subhead -->
<!--ISBN=1576101746//-->
<!--TITLE=Michael Abrash's Graphics Programming Black Book Special Edition//-->
<!--AUTHOR=Michael Abrash//-->
<!--PUBLISHER=The Coriolis Group, Inc.//-->
<!--CHAPTER=09//-->
<!--PAGES=178-180//-->
<!--UNASSIGNED1//-->
<!--UNASSIGNED2//--></HEAD><BODY LINK=#0000FF ALINK=#000099 VLINK=#0000FF BGCOLOR=#FFFFFF>
<CENTER>
<TABLE BORDER>
<TR>
<TD><A HREF="09-03.html">Previous</A></TD>
<TD><A HREF="../index.html">Table of Contents</A></TD>
<TD><A HREF="09-05.html">Next</A></TD>
</TR>
</TABLE>
</CENTER>
<P><BR></P>
<P><B>LISTING 9.2 L9-2.ASM</B></P>
<!-- CODE //-->
<PRE>
; Searches a text buffer for a text string. Uses REPNZ SCASB to scan
; the buffer for locations that match a specified character of the
; searched-for string, then uses REPZ CMPS to check fully only those
; locations that REPNZ SCASB has identified as potential matches.
;
; C small model-callable as:
; unsigned char * FindString(unsigned char * Buffer,
; unsigned int BufferLength, unsigned char * SearchString,
; unsigned int SearchStringLength,
; unsigned int ScanCharOffset);
;
; Returns a pointer to the first match for SearchString in Buffer,or
; a NULL pointer if no match is found. Buffer should not start at
; offset 0 in the data segment to avoid confusing a match at 0 with
; no match found.
Parms struc
dw 2 dup(?) ;pushed BP/return address
Buffer dw ? ;pointer to buffer to search
BufferLength dw ? ;length of buffer to search
SearchString dw ? ;pointer to string for which to search
SearchStringLength dw ? ;length of string for which to search
ScanCharOffset dw ? ;offset in string of character for
; which to scan
Parmsends
.model small
.code
public _FindString
_FindStringprocnear
push bp ;preserve caller&#146;s stack frame
mov bp,sp ;point to our stack frame
push si ;preserve caller&#146;s register variables
push di
cld ;make string instructions increment pointers
mov si,[bp&#43;SearchString] ;pointer to string to search for
mov cx,[bp&#43;SearchStringLength] ;length of string
jcxz FindStringNotFound ;no match if string is 0 length
mov dx,[bp&#43;BufferLength] ;length of buffer
sub dx,cx ;difference between buffer and search
; lengths
jc FindStringNotFound ;no match if search string is
; longer than buffer
inc dx ; difference between buffer and search string
; lengths, plus 1 (# of possible string start
; locations to check in the buffer)
mov di,ds
mov es,di
mov di,[bp&#43;Buffer] ;point ES:DI to buffer to search thru
mov bx,[bp&#43;ScanCharOffset] ;offset in string of character
; on which to scan
add di,bx ;point ES:DI to first buffer byte to scan
mov al,[si&#43;bx] ;put the scan character in AL
inc bx ;set BX to the offset back to the start of the
; potential full match after a scan match,
; accounting for the 1-byte overrun of
; REPNZ SCASB
FindStringLoop:
mov cx,dx ;put remaining buffer search length in CX
repnz scasb ;scan for the scan byte
jnz FindStringNotFound ;not found, so there&#146;s no match
;found, so we have a potential match-check the
; rest of this candidate location
push di ;remember the address of the next byte to scan
mov dx,cx ;set aside the remaining length to search in
; the buffer
sub di,bx ;point back to the potential start of the
; match in the buffer
mov si,[bp&#43;SearchString] ;point to the start of the string
mov cx,[bp&#43;SearchStringLength] ;string length
shr cx,1 ;convert to word for faster search
jnc FindStringWord ;do word search if no odd byte
cmpsb ;compare the odd byte
jnz FindStringNoMatch ;odd byte doesn&#146;t match, so we
; haven&#146;t found the search string here
FindStringWord:
jcxz FindStringFound ;if the string is only 1 byte long,
; we&#146;ve found a match
repz cmpsw ;check the rest of the string a word at a time
jz FindStringFound ;it&#146;s a match
FindStringNoMatch:
pop di ;get back pointer to the next byte to scan
and dx,dx ;is there anything left to check?
jnz FindStringLoop ;yes-check next byte
FindStringNotFound:
sub ax,ax ;return a NULL pointer indicating that the
jmp FindStringDone ; string was not found
FindStringFound:
pop ax ;point to the buffer location at which the
sub ax,bx ; string was found (earlier we pushed the
; address of the byte after the scan match)
FindStringDone:
pop di ;restore caller&#146;s register variables
pop si
pop bp ;restore caller&#146;s stack frame
ret
_FindStringendp
end
</PRE>
<!-- END CODE //-->
<P><B>LISTING 9.3 L9-3.C</B></P>
<!-- CODE //-->
<PRE>
/* Program to exercise buffer-search routines in Listings 9.1 &amp 9.2 */
#include &ltstdio.h&gt
#include &ltstring.h&gt
#define DISPLAY_LENGTH 40
extern unsigned char * FindString(unsigned char *, unsigned int,
unsigned char *, unsigned int, unsigned int);
void main(void);
static unsigned char TestBuffer[] = &#147;When, in the course of human \
events, it becomes necessary for one people to dissolve the \
political bands which have connected them with another, and to \
assume among the powers of the earth the separate and equal station \
to which the laws of nature and of nature&#146;s God entitle them...&#148;;
void main() {
static unsigned char TestString[] = &#147;equal&#148;;
unsigned char TempBuffer[DISPLAY_LENGTH&#43;1];
unsigned char *MatchPtr;
/* Search for TestString and report the results */
if ((MatchPtr = FindString(TestBuffer,
(unsigned int) strlen(TestBuffer), TestString,
(unsigned int) strlen(TestString), 1)) == NULL) {
/* TestString wasn&#146;t found */
printf(&#147;\&#148;%s\&#147; not found\n&#148;, TestString);
} else {
/* TestString was found. Zero-terminate TempBuffer; strncpy
won&#146;t do it if DISPLAY_LENGTH characters are copied */
TempBuffer[DISPLAY_LENGTH] = 0;
printf(&#147;\&#148;%s\&#147; found. Next %d characters at match:\n\&#148;%s\&#147;\n&#148;,
TestString, DISPLAY_LENGTH,
strncpy(TempBuffer, MatchPtr, DISPLAY_LENGTH));
}
}
</PRE>
<!-- END CODE //-->
<P><BR></P>
<CENTER>
<TABLE BORDER>
<TR>
<TD><A HREF="09-03.html">Previous</A></TD>
<TD><A HREF="../index.html">Table of Contents</A></TD>
<TD><A HREF="09-05.html">Next</A></TD>
</TR>
</TABLE>
</CENTER>
<hr width="90%" size="1" noshade>
<div align="center">
<font face="Verdana,sans-serif" size="1">Graphics Programming Black Book &copy; 2001 Michael Abrash</font>
</div>
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