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bsavelib.pas
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bsavelib.pas
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(* Data Meaning
'BYTE Magic number (always 0xFD, 253)
'INT Segment. Set to 0x9999 by modern versions.
'INT Offset is always 0
'INT Length, the number of bytes
Article: Q34407
Product(s): See article
Version(s): 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom B_GWBasicI | mspl13_basic
Last Modified: 9-JAN-1991
A file saved with the BSAVE statement has a 7-byte header with the
following hexadecimal format:
ww xx xx yy yy zz zz
ww: A signature byte equal to 253, which tells DOS and other
programs that this is a BASIC BSAVE/BLOAD format file.
xx xx: The segment address from the last BSAVE.
yy yy: The offset address from the last BSAVE.
zz zz: The number of bytes BSAVEd.
This information applies to Microsoft QuickBASIC versions 3.00, 4.00,
4.00b, and 4.50 for MS-DOS; to Microsoft BASIC Compiler versions 6.00
and 6.00b for MS-DOS; and to Microsoft BASIC Professional Development
System (PDS) versions 7.00 and 7.10 for MS-DOS.
This information is provided as is. The BSAVE format is not guaranteed
to be the same in a future release.
Microsoft GW-BASIC Interpreter (versions 3.20, 3.22, and 3.23) uses
the same 7-byte header string, and also repeats the 7-byte string,
appending it after the final data byte. BASICA (provided in IBM or
Compaq ROM on some computer models) does not repeat the 7-byte string
at the end. GW-BASIC and BASICA both terminate the file with ASCII 26,
also known as a CTRL+Z character (hex 1A). QuickBASIC and Microsoft
BASIC Compiler don't append CTRL+Z or repeat the 7-byte string at the
end.
To determine whether a file was BSAVEd by GW-BASIC, BASICA, or
QuickBASIC, compare the length of the memory saved against the file
length. The difference is 15 bytes in GW-BASIC, 7 bytes in QuickBASIC,
and 8 bytes in BASICA.
Despite the slight format differences, files BSAVEd under any of the
three above BASIC dialects correctly BLOAD into each other BASIC.
*)
unit bsavelib;
{PACKED RECORDS 1}
{$H-}
Interface
const
MaxBSaveSize = 32767;
function CreateBSaveObj(infile,outfile : string) : word;
function ValidBSaveSource(filename : string) : boolean;
Implementation
type
BsvRec = Record
Magic : Byte;
Seg : Word;
Off : Word;
Length : Word;
end;
Var
InFileMemPtr : Pointer;
InFileSize : Word;
(* we could allocate less memory - but this just a small app - 32Kb is no big deal *)
Procedure GetTheMemory;
begin
GetMem(InFileMemPtr,MaxBsaveSize);
if InFileMemPtr = NIL then
begin
Writeln('Failed to Allocate Enough Memeory, we need ',MaxBSaveSize,' bytes!');
end;
end;
Procedure FreeTheMemory;
begin
if InFileMemPtr<>NIL then
begin
Freemem(InFileMemPtr,MaxBsaveSize);
end;
end;
Procedure FailAndCleanUp;
begin
FreeTheMemory;
writeln('Looks like something went wrong - not sure what to say.');
halt;
end;
function ValidBSaveSource(filename : string) : boolean;
var
F : File;
valid : boolean;
begin
valid:=true;
Assign(F,filename);
{$I-}
Reset(F,1);
if FileSize(F) > MaxBSavesize then valid:=false;
Close(f);
{$I+}
if IOResult <> 0 then valid:=false;
result:=valid;
end;
Procedure CheckSize(filename : string);
var
F : File;
begin
Assign(F,filename);
{$I-}
Reset(F,1);
if FileSize(F) > 32767 then
begin
writeln('Source file too big. Must be ',MaxBSaveSize,' bytes or less!');
Close(F);
FreeTheMemory;
Halt;
end;
Close(f);
{$I+}
if IOResult <> 0 then
begin
FailAndCleanUp;
end;
end;
function ReadFile(filename : string) : word;
var
F : File;
RSize : Word;
begin
Assign(F,filename);
{$I-}
Reset(F,1);
BlockRead(F,InFileMemPtr^,MaxBSaveSize,RSize);
close(F);
{$I+}
if IOResult <> 0 then
begin
FailAndCleanUp;
end;
InFileSize:=RSize;
result:=IORESULT;
end;
function WriteFile(filename : string) : word;
var
F : File;
WSize : Word;
Bsv :BsvRec;
begin
Bsv.Magic:=$FD; (* 253 *)
Bsv.Seg:=$9999;
Bsv.Off:=$0;
Bsv.Length:=InFileSize;
Assign(F,filename);
{$I-}
Rewrite(F,1);
BlockWrite(F,Bsv,sizeof(Bsv));
BlockWrite(F,InFileMemPtr^,InFileSize,WSize);
BlockWrite(F,Bsv,sizeof(Bsv));
close(F);
{$I+}
if IOResult <> 0 then
begin
FailAndCleanUp;
end;
result:=IORESULT;
end;
function CreateBSaveObj(infile,outfile : string) : word;
var
error : word;
begin
// CheckSize(InFile);
result:=0;
GetTheMemory;
error:=ReadFile(InFile);
if error = 0 then
begin
error:=WriteFile(OutFile);
end;
FreeTheMemory;
result:=error;
end;
begin
end.