225 lines
7.9 KiB
Plaintext
225 lines
7.9 KiB
Plaintext
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unit OvrUMB;
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{ Unit OvrUMB : Uses an upper memory block as overlay buffer }
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{ }
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{ Version 1.2 (15/09/94) }
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{ }
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{ Author : Jean-Marc Lasgouttes }
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{ }
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{ e-mail : Jean-Marc.Lasgouttes@inria.fr }
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{$A+,F-,O-,S-}
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interface
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uses Overlay;
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Procedure OvrSetBufUMB(Size:longint);
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{Frees the current overlay buffer (which must be before the heap),
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allocates a new buffer of Size bytes in upper memory and sets the
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overlay manager to use this buffer. This is only possible if the
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heap is empty and no overlays are currently loaded. This procedure
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must not be used if the buffer has been already reallocated
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somewhere
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#OvrMovBufToUMB# is an automatic version of this procedure that generate
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more efficient code.}
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Procedure OvrMovBufToUMB;
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{Same procedure as #OvrSetBufUMB#, except that the size of the UMB buffer
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is the biggest available upper memory block. No rellocation occurs if
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the biggest block is smaller than the current overlay buffer. This is the
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most convenient procedure to use.}
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Function UMB_MaxAvail:longint;
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{Returns the size of the biggest available upper memory block}
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implementation
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const OvrUMBSeg:word=0; {The Segment of the overlay buffer}
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var OldExitProc:Pointer; {The old ExitProc (surprise!)}
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SaveMemStrat, {Temporary variables to save system state}
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SaveUMBLink:word;
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Function ChangeMemStrat:boolean; assembler;
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{Save the current memory allocation strategy and change it in order
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to allocate upper memory}
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asm
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MOV AX, 5800h {Save memory allocation strategy}
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INT 21h
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MOV SaveMemStrat, AX
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MOV AX, 5802h {Save UMB Link state}
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INT 21h
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MOV SaveUMBLink, AX
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JC @@1 {If this function is not recognized}
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{ then DOS version <5 : Error}
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MOV AX, 5801h {Set memory allocation strategy to}
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MOV BX, 40h { use only upper memory}
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INT 21h
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MOV AX, 5803h {Add UMB to DOS memory chain}
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MOV BX, 1
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INT 21h
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JNC @@2 {Error: no UMB provider}
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@@1:MOV AX, false {Return an error}
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JMP @@3
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@@2:MOV AX, true {Return success}
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@@3:
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end;
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Procedure ResetMemStrat; assembler;
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{Restore the memory allocation strategy as it was before the call to
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ChangeMemStrat}
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asm
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MOV AX, 5801h {Reset the memory allocation strategy}
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MOV BX, SaveMemStrat
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INT 21h
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MOV AX, 5803h {Reset the UMB link state}
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MOV BX, SaveUMBLink
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INT 21h
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end;
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Procedure ReleaseUMB(UMBSeg:word); assembler;
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{Releases the block corresponding to UMBSeg if UMBSeg<>0}
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asm
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MOV AX, UMBSeg {If the segment is zero, do nothing}
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CMP AX, 0
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JZ @@1
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MOV AX, 5802h {Save UMB Link state}
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INT 21h
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MOV SaveUMBLink, AX
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MOV AX, 5803h
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MOV BX, 0 {Remove UMB from DOS memory chain}
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INT 21h
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MOV AH, 49h {Free block used by UMBSeg}
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MOV ES, UMBSeg
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INT 21h
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MOV AX, 5803h {Reset UMB link state}
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MOV BX, SaveUMBLink
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INT 21h
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@@1:
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end;
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Procedure PrimSetBufUMB(Size:word); assembler;
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{The basic procedure called by OvrSetBufUMB and OvrMovBufToUMB. Size
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is given in paragraphs.}
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asm
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XOR AX, AX {Check for errors: }
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CMP AX, OvrDOSHandle { Is the Overlay file opened?}
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JZ @@3
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CMP AX, OvrLoadList { Are there some Overlays loaded?}
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JNZ @@3
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MOV AX, OvrHeapEnd { Is the buffer already rellocated?}
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CMP AX, WORD PTR HeapOrg+2
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JNZ @@3
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CMP AX, WORD PTR HeapPtr+2 { Is there something in the heap?}
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JNZ @@3
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MOV AH, 48h {Allocate UMBSize segments of memory}
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MOV BX, Size
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INT 21h
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JNC @@1
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MOV AX, ovrNoMemory {Not enough UMB}
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JMP @@2
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@@1:MOV OvrUMBSeg, AX {Keep the segment in OvrUMBSeg}
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MOV AX, OvrHeapOrg
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MOV WORD PTR HeapOrg+2, AX {Seg(HeapOrg):=OvrHeapOrg}
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MOV WORD PTR HeapPtr+2, AX {Seg(HeapPtr):=OvrHeapOrg}
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MOV WORD PTR FreeList+2, AX {Seg(FreeList):=OvrHeapOrg}
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XOR AX, AX
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MOV WORD PTR HeapOrg, AX {Ofs(HeapOrg):=0}
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MOV WORD PTR HeapPtr, AX {Ofs(HeapPtr):=0}
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MOV WORD PTR FreeList, AX {Ofs(FreeList):=0}
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MOV AX, OvrUMBSeg
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MOV OvrHeapOrg, AX {OvrHeapOrg:=OvrUMBSeg }
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MOV OvrHeapPtr, AX {OvrHeapPtr:=OvrUMBSeg }
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ADD AX, Size
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MOV OvrHeapEnd, AX {OvrHeapEnd:=OvrUMBSeg+Size}
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MOV AX, ovrOK {Success}
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JMP @@2
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@@3:MOV AX, ovrError
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@@2:MOV OvrResult, AX {Put the result in OvrResult}
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end;
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Function UMB_MaxAvail:longint; assembler;
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asm
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CALL ChangeMemStrat {Allow the use of upper memory}
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CMP AX, false
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JZ @@1 {if it not possible, return 0}
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MOV AH, 48h {Try to allocate too much memory}
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MOV BX, 0FFFFh
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INT 21h {BX contains the size of the biggest}
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MOV AX, BX { available block}
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XOR DX, DX
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SHL AX, 1 {Multiply by 16 and put the result}
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RCL DX, 1 { in DX:AX}
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SHL AX, 1
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RCL DX, 1
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SHL AX, 1
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RCL DX, 1
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SHL AX, 1
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RCL DX, 1
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JMP @@2
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@@1:XOR AX, AX
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XOR DX, DX
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@@2:PUSH AX
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PUSH DX
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CALL ResetMemStrat {Reset the memory allocation strategy}
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POP DX
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POP AX
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end;
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Procedure OvrSetBufUMB(Size:longint); assembler;
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asm
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CALL ChangeMemStrat {Allow the use of upper memory}
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CMP AX, false
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JZ @@1 {If it is impossible, abort}
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MOV AX, WORD PTR Size {Transform Size}
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MOV DX, WORD PTR Size+2 { into a number of paragraphs}
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MOV CL, 04h
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SHR AX, CL
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ROR DX, CL
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AND DX, 0F000h
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OR AX, DX { the result is in AX}
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CMP AX, OvrHeapSize {If AX < OvrHeapSize --> Error}
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JB @@1
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PUSH AX
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CALL PrimSetBufUMB {Actually allocate and set the buffer}
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JMP @@2
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@@1:MOV AX, ovrError {Report an Error}
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MOV OvrResult, AX
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@@2:CALL ResetMemStrat
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end;
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Procedure OvrMovBufToUMB; assembler;
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asm
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CALL ChangeMemStrat {Allow the use of upper memory}
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CMP AX, false
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JZ @@1 {If it is impossible, abort}
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MOV AH, 48h {Try to allocate too much memory}
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MOV BX, 0FFFFh
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INT 21h {BX contains the size of the biggest}
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{ available upper memory block}
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MOV AX, OvrHeapEnd {Compute the size of the}
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SUB AX, OvrHeapOrg { current Overlay buffer}
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CMP AX, BX {Is the UMB bigger than the current buffer?}
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JNB @@1 {If not, abort}
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PUSH BX
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CALL PrimSetBufUMB {Actually allocate and set the buffer}
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JMP @@2
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@@1:MOV OvrResult, OvrNoMemory
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@@2:CALL ResetMemStrat
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end;
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Procedure OvrUMBExitProc; far;
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begin
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ExitProc:=OldExitProc; {Chain to the old exit handler}
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ReleaseUMB(OvrUMBSeg); {Release the overlay buffer}
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end;
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begin
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OldExitProc:=ExitProc;
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ExitProc:=@OvrUMBExitProc; {Release the UMB on exit}
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end.
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