sys7.1-doc-wip/Tools/CRCPatch.a
2019-07-27 22:37:48 +08:00

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