220 lines
5.6 KiB
NASM
220 lines
5.6 KiB
NASM
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;
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; --------------------------------------------------
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; free - release a block of heap
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; --------------------------------------------------
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;
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IDT cfree
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DEF cfree
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DEF free
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DEF _nfree
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IF UPPER
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DEF CFREE
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DEF FREE
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ENDIF
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FREF $$FREE$$
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;
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; free(ptr) - release a block of heap
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;
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cfree equ $
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CFREE EQU $
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free equ $
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_nfree equ $
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FREE MOV SI,SP
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MOV BX,[SI][%PARM1-2]
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CALLFAR $$FREE$$
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XOR AX,AX
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RETSEG
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END
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;
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; $_FREE(ptr);
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; ptr is address of a pointer
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; block is released and pointer set to nil
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;
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IDT $_free
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DEF $_FREE
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FREF $$FREE$$
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$_FREE PUSH BP
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MOV BP,SP
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MOV BX,[BP][%PARM1] ; pointer address
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MOV BX,[BX] ; value of pointer
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CALLFAR $$FREE$$
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MOV BX,[BP][%PARM1] ; pointer address
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MOV [BX],0
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POP BP
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RETSEG
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END
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;
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; ------------------------------------------------------------
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;
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; FREE$$
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; RELEASE A HEAP PACKET
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; INPUTS:
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; BX - POINTER TO THE PACKET BEGIN RETURNED
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; OUTPUTS:
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; NONE
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; REGISTERS USED:
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; DI, SI, BP ARE PRESERVED
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;
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;
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IDT $$FREE$$
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DEF $$FREE$$
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REF $$HPTERM
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FREF $_FATAL
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REF $$HMIN
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REF $$HMAX
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REF $$CURH
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REF $$FREE
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REF errno
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;
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; CHECK FOR SIZE, NIL POINTER
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;
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$$FREE$$ TEST BX,BX
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JNZ FREE01
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RETSEG ; NIL - EXIT
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FREE01 SUB BX,%2 ; POINT TO LENGTH FIELD
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;
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; CHECK POINTER AGAINST LOWER BOUND OF HEAP - ERROR IF LESS
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;
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CMP BX,[$$HMIN]
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JB INVPKT
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;
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; GET LENGTH OF THE PACKET
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;
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FR01 MOV CX,[BX]
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TEST CL,%1 ; CHECK ALLOCATED FLAG
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JZ INVPKT ; NOT ALLOCATED
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AND CL,%>FE ; RESET ALLOCATION FLAG
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MOV AX,BX
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ADD AX,CX ; AX POINTS TO NEXT PACKET
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;
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; CHECK PTR + SIZE OF PACKET AGAINST HEAP UPPER BOUND
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;
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CMP AX,[$$HMAX]
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JA INVPKT
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;
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; BX = ADDRESS OF RELEASED PACKET
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; CX = SIZE OF RELEASED PACKET
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; AX = ADDRESS OF NEXT PACKET
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;
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; PACKET IS VALID, RELEASE IT
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;
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FR02 SUB [$$CURH],CX ; SUBTRACT FROM CURRENT
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;
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; IS NEXT PACKET ALLOCATED?
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;
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MOV DX,BX
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MOV BX,AX
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TEST [BX],%1 ; CHECK ALLOCATION FLAG
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JNZ FR03 ; ALLOCATED
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;
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; NEXT PACKET IS AVAILABLE, MERGE CURRENT AND NEXT PACKETS
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;
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MOV AX,[BX] ; GET SIZE OF NEXT PACKET
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TEST AX,AX ; CHECK FOR ZERO
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JZ FR03 ; DON'T MERGE WITH ANCHOR
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ADD CX,AX ; CX = SIZE OF COMBINATION
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;
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; ASSIGN FREELIST TO NEW PACKET
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;
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MOV [$$FREE],DX
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;
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; FIND THE PREVIOUS PACKET THAT IS FREE AND CLOSEST
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; TO THE PACKET BEING RELEASED
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;
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MOV AX,[BX][2] ; GET NEXT FIELD FOR CURRENT
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MOV BX,[BX][4] ; PREV LINK OF NEXT FREE PKT
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;
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; AT THIS POINT:
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; DX = CURRENT PACKET
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; AX = NEXT PACKET
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; BX = PREVIOUS PACKET
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; CX = LENGTH OF CURRENT
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;
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JMPS FR05 ; CHECK FOR LAST PACKET FREE
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;
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; NEXT PACKET IS NOT AVAILABLE
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; FIND THE NEXT PACKET THAT IS AVAILABLE TO GET
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; ITS LAST PACKET POINTER
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; BX = NEXT PACKET
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; CX = PACKET SIZE
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; DX = CURRENT PACKET
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;
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FR03 MOV AX,[BX] ; GET SIZE OF NEXT PACKET
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AND AL,%>FE ; REMOVE ALLOCATION FLAG
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ADD BX,AX ; POINT TO FOLLOWING
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TEST [BX],%1 ; CHECK NEXT PACKET ALLOCATION
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JNZ FR03 ; LOOP UNTIL FREE
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;
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; BX NOW POINTS TO THE NEXT FREE PACKET
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; GET THE LAST POINTER FROM THE NEXT PACKET
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;
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MOV AX,BX
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MOV BX,[BX][4] ; GET PREV POINTER
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;
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; AT THIS POINT:
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; AX = NEXT PACKET
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; CX = PACKET LENGTH
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; DX = CURRENT PACKET
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; BX = LAST PACKET
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;
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;
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; CHECK LAST PACKET. IF THE LAST FREE PACKET IS CONTIGUOUS
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; WITH THE CURRENT PACKET, THEY CAN BE MERGED INTO A SINGLE
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; PACKET.
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;
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FR05 PUSH AX ; SAVE
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MOV AX,[BX] ; LENGTH OF PREVIOUS PKT
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ADD AX,BX ; AX <-- LAST+SIZE(LAST)
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CMP AX,DX
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JNZ FR06 ; CAN NOT JOIN
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;
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; THE LAST PACKET IS CONTIGUOUS WITH THE CURRENT PACKET,
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; MERGE THEM.
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;
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ADD CX,[BX] ; ADD LENGTHS
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MOV [BX],CX ; SET TOTAL LENGTH
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POP AX
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MOV [BX][2],AX ; SET NEXT PKT POINTER
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XCHG BX,AX
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MOV [BX][4],AX ; SET NEXT@.LAST TO MERGED PKT
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;
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; SET FREE LIST TO MERGED PACKET
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;
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MOV [$$FREE],AX
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RETSEG ; DONE
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;
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;
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; THE LAST PACKET IS NOT CONTIGUOUS WITH THE CURRENT PACKET
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; A NEW PACKET IS CREATED FOR THE PACKET BEING RELEASED.
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;
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; TOS = NEXT
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; DX = CURRENT
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; BX = PREVIOUS
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; CX = LENGTH
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;
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FR06 XCHG BX,DX
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MOV [BX],CX ; SET SIZE
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POP AX
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MOV [BX][2],AX ; SET NEXT POINTER
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MOV [BX][4],DX ; SET PREVIOUS
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XCHG BX,DX
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MOV [BX][2],DX ; SET PREV@.NEXT
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MOV BX,AX
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MOV [BX][4],DX ; SET NEXT@.LAST
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;
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; DONE
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;
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FREEX RETSEG
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;
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; INVALID PACKET POINTER
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;
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INVPKT MOV AX,E$PACKET
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MOV %[errno],AL
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TEST %[$$HPTERM],%>FF
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JZ FREEX
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PUSH AX
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CALLFAR $_FATAL
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POP AX
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RETSEG
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END
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