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132 lines
3.6 KiB
Plaintext
132 lines
3.6 KiB
Plaintext
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; File: CRCPatch.a
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;
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; Contains: This file does the CRC calculation.
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;
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; Written by: George Norman - 7/30/86
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;
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; Copyright: © 1986-1992 by Apple Computer, Inc. All rights reserved.
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;
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; Change History (most recent first):
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;
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; <SM4> 11/5/92 SWC Changed SlotEqu.a->Slots.a.
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; <SM3> 5/29/92 KW (jmp,H3) Made sure the crcCalc is not performed on zero-sized
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; <SM2> 5/29/92 kc Fix CalcCRC to allow decldata larger than 64k.
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; <1> 1/31/92 JSM first checked in
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;
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INCLUDE 'SysEQU.a'
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INCLUDE 'ROMEqu.a' ;Declaration ROM EQU's
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include 'Slots.a'
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;=====================================================================
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; _CalcCRC : Calculate CRC
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;
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; PROCEDURE _CalcCRC(SizeCode,DataPtr,crc);
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;=====================================================================
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_CalcCRC PROC EXPORT
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;VAR
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RetnAddr$a EQU A0
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DataPtr$a EQU A1
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crcAdrL$a EQU A2
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crcAdrH$a EQU A3
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Temp$a EQU A4
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TopOfData$a EQU A5
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SizeCode$d EQU D0
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crcPos$d EQU D1
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crc$d EQU D2
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Temp$d EQU D3
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Index$d EQU D4
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; Define stack-frame
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StackFrame RECORD {A6Link},DECR
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SizeCode DS.L 1 ;size of code
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DataPtr DS.L 1 ;pointer to data
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crc@ DS.L 1 ;VAR crc:longint
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Return DS.L 1 ;Return address
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A6Link DS.L 1 ;Old A6
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ENDR
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; Other
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dataPtr EQU $4 ; [handle] <SM3>
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;----------------------------------------------------------------------
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; _CalcCRC
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;----------------------------------------------------------------------
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;BEGIN
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WITH FHeaderRec, StackFrame
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; Allocate local vars
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LINK A6,#0
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MOVEM.L A2-A5/D3-D4,-(SP) ;Save registers
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; Calculate the address of the crc value.
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MOVE.L SizeCode(A6),TopOfData$a ;TopOfData$a := Top of data
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ADD.L DataPtr(A6),TopOfData$a
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MOVE.L TopOfData$a,crcAdrL$a ;crcAdrL$a := TopOfData$a - (fhBlockSize-FH_crc) {Addr of crc MSB}
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SUB.L #fhBlockSize-fhCRC,crcAdrL$a
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MOVE.L crcAdrL$a,crcAdrH$a
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ADD.L #3,crcAdrH$a ;Addr of crc LSB
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; Determine the size of the declaration data to be checked.
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MOVE.L TopOfData$a,Temp$a ;Temp$a := TopOfData$a - (fhBlockSize-FH_Length) {Addr of Length field}
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SUB.L #fhBlockSize-fhLength,Temp$a ;Index := length of crc data.
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MOVE.L (Temp$a),Index$d ;If there’s nothing to do (i.e., Index == 0), <SM3>
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BEQ.S theEnd ; then just leave. <SM3>
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MOVEQ #0,crc$d ;crc$d := 0
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MOVE.L DataPtr(A6),DataPtr$a ;DataPtr$a := pointer to data
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MOVE.L SizeCode(A6),Temp$d ;Adjust DataPtr$a
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SUB.L Index$d,Temp$d
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ADD.L Temp$d,DataPtr$a
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; Calc the crc value.
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MOVEQ #0,Temp$d ;Temp$d := 0
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;REPEAT
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Repeat ROL.L #1,crc$d ; Rotate-left the crc value.
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CMP.L crcAdrL$a,DataPtr$a ; IF DataPtr$a IN [crcAdrL$a..crcAdrH$a] THEN
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BLT.S C10
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CMP.L crcAdrH$a,DataPtr$a
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BGT.S C10
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ADDQ.L #1,DataPtr$a ; DataPtr$a := DataPtr$a + 1 {Do not include crc in calculation}
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BRA.S Until
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; ELSE
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C10 MOVE.B (DataPtr$a)+,Temp$d ; Temp$d := DataPtr$a^; DataPtr$a := DataPtr$a + 1
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ADD.L Temp$d,crc$d ; crc$d := crc$d + Temp$d
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Until Subq.l #1,Index$d ; <SM3>
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Bne.s Repeat ; <SM3>
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;UNTIL Index$d < 0
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; Patch in the crc result.
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MOVE.L crc$d,(crcAdrL$a)
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; Move crc result to calling routine.
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MOVE.L crc@(A6),Temp$a
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MOVE.L crc$d,(Temp$a)
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; Restore globals, cleanup stack & return
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theEnd MOVEM.L (SP)+,A2-A5/D3-D4 ;Restore registers <SM3>
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UNLK A6 ;Clear stack frame of local vars
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MOVE.L (SP)+,RetnAddr$a ;Remove return address
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ADD.L #12,SP ;Clear stack-frame of parameters
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JMP (RetnAddr$a) ;Return
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ENDWITH
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ENDP
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END
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