case off
	
	mcopy /usr/local/ainclude/m16.smartstacks
	mcopy crc.mac

root	start
	end


* calculate the crc.  returns value in little endian format.
* unsigned pascal long PngCrc(long crc, char *data, int len)

PngCrc	start
	
	using CRCTable
	DefineStack

	FixStack

	BegParms
length	Word
data	LongWord
crc	LongWord
	EndParms

	BeginStack


* for (n = 0; n < len; n++)
*   crc = CrcTable[(crc ^ data[n]) & 0xff] ^ (crc >> 8);

	ldy #0
loop	cpy <length
	beq eloop

*	x  = (crc ^ data[n]) & 0x00ff
	lda [<data],y
*	and #$00ff		; doesn't matter...
	eor <crc
	and #$00ff

	asl a			; x 4 to index.
	asl a
	tax			; save

*	crc = crc >> 8
	lda <crc
	xba
	and #$00ff
	sta <crc

* move the 8 bits from crc+2.low --> crc.hi
	lda <crc+2
	xba
	pha			;save ...
	and #$ff00
*	ora <crc
*	sta <crc
	tsb <crc

	pla			; restore
	and #$00ff
	sta <crc+2

*	crc = crc ^ CrcTable[x]

	lda Table,x
	eor <crc
	sta <crc

	lda Table+2,x
	eor <crc+2
	sta <crc+2

	iny
	bra loop

eloop	anop


* return crc ^ 0xffffffff
*	lda <crc
*	eor #$ffff
*	tay

*	lda <crc+2
*	eor #$ffff
*	tax

	ldx <crc+2
	ldy <crc

	EndStack
	tya
	rtl
	end

* calculate the crc.  returns value in little endian format.
* unsigned pascal long AdlerCrc(long crc char *data, int len)

AdlerCrc	start
	
	DefineStack

	FixStack

	BegParms
length	Word
data	LongWord
crc	LongWord
	EndParms

	BeginStack


* for (n = 0; n < length; n++) {
*  s1 = (s1 + data[n]) % 65521
*  s2 = (s1 + s2) % 65521
* }
*
* we have a slight problem, however.  Since a 16-bit integer maxes
* out at 65535, there's a 240/255 probability the number will overflow.
* to catch that we simply check for the carry bit and if it's set,
* add 15 (65536 + x - 65521 = x + 15)

	ldy #0
loop	cpy <length
	beq eloop

	lda [data],y
	and #$00ff
	clc
	adc <crc
        bcc check1

* overflow.  a = a + 65536 - 65521.
	clc
	adc #15
	bra s1

check1	anop
	cmp #65521
	bcc s1

	sbc #65521	; carry bit still set from cmp

s1	anop

	sta <crc
	clc
	adc <crc+2
	bcc check2

* overflow.  a = a + 65536 - 65521.
	clc
	adc #15
	bra s2

check2	anop
	cmp #65521
	bcc s2

	sbc #65521	; carry bit still set from cmp

s2	anop
	sta <crc+2

	iny
	bra loop

eloop	anop

	ldx <crc+2
	ldy <crc
	EndStack
	tya
	rtl
	end



CRCTable	Data
Table	anop
	dc i4'$00000000'
	dc i4'$77073096'
	dc i4'$ee0e612c'
	dc i4'$990951ba'
	dc i4'$076dc419'
	dc i4'$706af48f'
	dc i4'$e963a535'
	dc i4'$9e6495a3'
	dc i4'$0edb8832'
	dc i4'$79dcb8a4'
	dc i4'$e0d5e91e'
	dc i4'$97d2d988'
	dc i4'$09b64c2b'
	dc i4'$7eb17cbd'
	dc i4'$e7b82d07'
	dc i4'$90bf1d91'
	dc i4'$1db71064'
	dc i4'$6ab020f2'
	dc i4'$f3b97148'
	dc i4'$84be41de'
	dc i4'$1adad47d'
	dc i4'$6ddde4eb'
	dc i4'$f4d4b551'
	dc i4'$83d385c7'
	dc i4'$136c9856'
	dc i4'$646ba8c0'
	dc i4'$fd62f97a'
	dc i4'$8a65c9ec'
	dc i4'$14015c4f'
	dc i4'$63066cd9'
	dc i4'$fa0f3d63'
	dc i4'$8d080df5'
	dc i4'$3b6e20c8'
	dc i4'$4c69105e'
	dc i4'$d56041e4'
	dc i4'$a2677172'
	dc i4'$3c03e4d1'
	dc i4'$4b04d447'
	dc i4'$d20d85fd'
	dc i4'$a50ab56b'
	dc i4'$35b5a8fa'
	dc i4'$42b2986c'
	dc i4'$dbbbc9d6'
	dc i4'$acbcf940'
	dc i4'$32d86ce3'
	dc i4'$45df5c75'
	dc i4'$dcd60dcf'
	dc i4'$abd13d59'
	dc i4'$26d930ac'
	dc i4'$51de003a'
	dc i4'$c8d75180'
	dc i4'$bfd06116'
	dc i4'$21b4f4b5'
	dc i4'$56b3c423'
	dc i4'$cfba9599'
	dc i4'$b8bda50f'
	dc i4'$2802b89e'
	dc i4'$5f058808'
	dc i4'$c60cd9b2'
	dc i4'$b10be924'
	dc i4'$2f6f7c87'
	dc i4'$58684c11'
	dc i4'$c1611dab'
	dc i4'$b6662d3d'
	dc i4'$76dc4190'
	dc i4'$01db7106'
	dc i4'$98d220bc'
	dc i4'$efd5102a'
	dc i4'$71b18589'
	dc i4'$06b6b51f'
	dc i4'$9fbfe4a5'
	dc i4'$e8b8d433'
	dc i4'$7807c9a2'
	dc i4'$0f00f934'
	dc i4'$9609a88e'
	dc i4'$e10e9818'
	dc i4'$7f6a0dbb'
	dc i4'$086d3d2d'
	dc i4'$91646c97'
	dc i4'$e6635c01'
	dc i4'$6b6b51f4'
	dc i4'$1c6c6162'
	dc i4'$856530d8'
	dc i4'$f262004e'
	dc i4'$6c0695ed'
	dc i4'$1b01a57b'
	dc i4'$8208f4c1'
	dc i4'$f50fc457'
	dc i4'$65b0d9c6'
	dc i4'$12b7e950'
	dc i4'$8bbeb8ea'
	dc i4'$fcb9887c'
	dc i4'$62dd1ddf'
	dc i4'$15da2d49'
	dc i4'$8cd37cf3'
	dc i4'$fbd44c65'
	dc i4'$4db26158'
	dc i4'$3ab551ce'
	dc i4'$a3bc0074'
	dc i4'$d4bb30e2'
	dc i4'$4adfa541'
	dc i4'$3dd895d7'
	dc i4'$a4d1c46d'
	dc i4'$d3d6f4fb'
	dc i4'$4369e96a'
	dc i4'$346ed9fc'
	dc i4'$ad678846'
	dc i4'$da60b8d0'
	dc i4'$44042d73'
	dc i4'$33031de5'
	dc i4'$aa0a4c5f'
	dc i4'$dd0d7cc9'
	dc i4'$5005713c'
	dc i4'$270241aa'
	dc i4'$be0b1010'
	dc i4'$c90c2086'
	dc i4'$5768b525'
	dc i4'$206f85b3'
	dc i4'$b966d409'
	dc i4'$ce61e49f'
	dc i4'$5edef90e'
	dc i4'$29d9c998'
	dc i4'$b0d09822'
	dc i4'$c7d7a8b4'
	dc i4'$59b33d17'
	dc i4'$2eb40d81'
	dc i4'$b7bd5c3b'
	dc i4'$c0ba6cad'
	dc i4'$edb88320'
	dc i4'$9abfb3b6'
	dc i4'$03b6e20c'
	dc i4'$74b1d29a'
	dc i4'$ead54739'
	dc i4'$9dd277af'
	dc i4'$04db2615'
	dc i4'$73dc1683'
	dc i4'$e3630b12'
	dc i4'$94643b84'
	dc i4'$0d6d6a3e'
	dc i4'$7a6a5aa8'
	dc i4'$e40ecf0b'
	dc i4'$9309ff9d'
	dc i4'$0a00ae27'
	dc i4'$7d079eb1'
	dc i4'$f00f9344'
	dc i4'$8708a3d2'
	dc i4'$1e01f268'
	dc i4'$6906c2fe'
	dc i4'$f762575d'
	dc i4'$806567cb'
	dc i4'$196c3671'
	dc i4'$6e6b06e7'
	dc i4'$fed41b76'
	dc i4'$89d32be0'
	dc i4'$10da7a5a'
	dc i4'$67dd4acc'
	dc i4'$f9b9df6f'
	dc i4'$8ebeeff9'
	dc i4'$17b7be43'
	dc i4'$60b08ed5'
	dc i4'$d6d6a3e8'
	dc i4'$a1d1937e'
	dc i4'$38d8c2c4'
	dc i4'$4fdff252'
	dc i4'$d1bb67f1'
	dc i4'$a6bc5767'
	dc i4'$3fb506dd'
	dc i4'$48b2364b'
	dc i4'$d80d2bda'
	dc i4'$af0a1b4c'
	dc i4'$36034af6'
	dc i4'$41047a60'
	dc i4'$df60efc3'
	dc i4'$a867df55'
	dc i4'$316e8eef'
	dc i4'$4669be79'
	dc i4'$cb61b38c'
	dc i4'$bc66831a'
	dc i4'$256fd2a0'
	dc i4'$5268e236'
	dc i4'$cc0c7795'
	dc i4'$bb0b4703'
	dc i4'$220216b9'
	dc i4'$5505262f'
	dc i4'$c5ba3bbe'
	dc i4'$b2bd0b28'
	dc i4'$2bb45a92'
	dc i4'$5cb36a04'
	dc i4'$c2d7ffa7'
	dc i4'$b5d0cf31'
	dc i4'$2cd99e8b'
	dc i4'$5bdeae1d'
	dc i4'$9b64c2b0'
	dc i4'$ec63f226'
	dc i4'$756aa39c'
	dc i4'$026d930a'
	dc i4'$9c0906a9'
	dc i4'$eb0e363f'
	dc i4'$72076785'
	dc i4'$05005713'
	dc i4'$95bf4a82'
	dc i4'$e2b87a14'
	dc i4'$7bb12bae'
	dc i4'$0cb61b38'
	dc i4'$92d28e9b'
	dc i4'$e5d5be0d'
	dc i4'$7cdcefb7'
	dc i4'$0bdbdf21'
	dc i4'$86d3d2d4'
	dc i4'$f1d4e242'
	dc i4'$68ddb3f8'
	dc i4'$1fda836e'
	dc i4'$81be16cd'
	dc i4'$f6b9265b'
	dc i4'$6fb077e1'
	dc i4'$18b74777'
	dc i4'$88085ae6'
	dc i4'$ff0f6a70'
	dc i4'$66063bca'
	dc i4'$11010b5c'
	dc i4'$8f659eff'
	dc i4'$f862ae69'
	dc i4'$616bffd3'
	dc i4'$166ccf45'
	dc i4'$a00ae278'
	dc i4'$d70dd2ee'
	dc i4'$4e048354'
	dc i4'$3903b3c2'
	dc i4'$a7672661'
	dc i4'$d06016f7'
	dc i4'$4969474d'
	dc i4'$3e6e77db'
	dc i4'$aed16a4a'
	dc i4'$d9d65adc'
	dc i4'$40df0b66'
	dc i4'$37d83bf0'
	dc i4'$a9bcae53'
	dc i4'$debb9ec5'
	dc i4'$47b2cf7f'
	dc i4'$30b5ffe9'
	dc i4'$bdbdf21c'
	dc i4'$cabac28a'
	dc i4'$53b39330'
	dc i4'$24b4a3a6'
	dc i4'$bad03605'
	dc i4'$cdd70693'
	dc i4'$54de5729'
	dc i4'$23d967bf'
	dc i4'$b3667a2e'
	dc i4'$c4614ab8'
	dc i4'$5d681b02'
	dc i4'$2a6f2b94'
	dc i4'$b40bbe37'
	dc i4'$c30c8ea1'
	dc i4'$5a05df1b'
	dc i4'$2d02ef8d'
	End