Contributor: DAVID STIDOLPH
(*
If you have the VCL source look at TMemoryStream - it is pretty efficient
for 286 code. If you are willing to only run on 386 machines you can use
386 32-bit addressing in assembly code to access the data. Following the
includion I have placed some assembly code I have written to do this. It
compiles under MASM and is linked with the {$L} directive. The reason I
wrote this code was for a WinG module I am still working on. Anyone is
welcome to use this code, but I would like to see work done using it.>The TMemoryStream has a property TMemoryStream.Memory, which returns a>pointer to the actual location of the data in memory. To access the >first byte I could just use TMemoryStream.Memory^>>The problem is: If I want to for example get bytes 15 to 21 out of the>stream, is there a way to point to the location of this data?>I do not want to use the Seek/Read function, as this is a lot slower>than using direct memory access.
*)
{$L move.obj}
procedure Move32(pSrc: Pointer; srcOffset: Longint; pDest: Pointer;
destOffset: Longint; len: Longint); external;
Assembly code (move.asm)
.MODEL large, PASCAL
.386
OPTION SCOPED
LPBYTE TYPEDEF FAR PTR BYTE
Move32 PROTO FAR PASCAL,
pSrc:LPBYTE, srcOffset:DWORD,
pDest: LPBYTE, destOffset:DWORD,
len:DWORD
.Code
Move32 PROC FAR PASCAL USES ds es esi edi,
pSrc: LPBYTE, srcOffset:DWORD,
pDest: LPBYTE, destOffset:DWORD,
len:DWORD
cld ;move forward through memory
mov esi,0 ;clear index registers - noteably the top of
mov edi,0 ;the 32 bit (upper 16 bits) registers.
lds si,pSrc ;load ds/si with pointer to base source
les di,pDest ;load es/di with pointer to base destination
add esi,srcOffset ;add in offset to desired point
add edi,destOffset ;add in offset to desired point
mov ecx,len ;get the length of the move
shr ecx,2 ;divide by 4 for DWORD moves
rep movsd ;if ecx is zero no move is done
mov ecx,len ;pick up length to do remainder
and ecx,3 ;only move 0-3 bytes
rep movsb ;if ecx is zero no move is done
retf ;far return
Move32 ENDP
END