2003-09-23 20:11:39 +00:00
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; Piotr Fusik, 18.11.2001
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;
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; unsigned long __fastcall__ adler32 (unsigned long adler, unsigned char* buf,
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; unsigned len);
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;
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.export _adler32
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.import incsp2, incsp4, popax, popeax
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.importzp sreg, ptr1, ptr2, tmp1
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BASE = 65521 ; largest prime smaller than 65536
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_adler32:
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; ptr2 = (len & 0xff) == 0 ? len : len + 0x100;
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tay
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beq @L1
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inx
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@L1: sta ptr2
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stx ptr2+1
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; ptr1 = buf
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jsr popax
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sta ptr1
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stx ptr1+1
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; if (buf == NULL) return 1L;
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ora ptr1+1
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beq @L0
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; s1 = adler & 0xFFFF; s2 = adler >> 16;
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jsr popeax
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; if (len == 0) return adler;
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ldy ptr2
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bne @L2
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ldy ptr2+1
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beq @RET
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@L2: ldy #0
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; s1 += *ptr++; if (s1 >= BASE) s1 -= BASE;
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@L3: clc
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adc (ptr1),y
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bcc @L4
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inx
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beq @L5 ; C flag is set
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@L4: cpx #>BASE
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bcc @L6
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cmp #<BASE
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bcc @L6
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inx ; ldx #0
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@L5: sbc #<BASE ; C flag is set
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clc
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@L6: sta tmp1
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; s2 += s1; if (s2 >= BASE) s2 -= BASE;
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adc sreg ; C flag is clear
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sta sreg
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txa
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adc sreg+1
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sta sreg+1
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bcs @L7
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cmp #>BASE
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bcc @L8
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lda sreg
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cmp #<BASE
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bcc @L8
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@L7: lda sreg
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sbc #<BASE ; C flag is set
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sta sreg
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lda sreg+1
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sbc #>BASE
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sta sreg+1
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@L8: lda tmp1
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iny
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bne @L9
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inc ptr1+1
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@L9: dec ptr2
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bne @L3
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dec ptr2+1
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bne @L3
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; return (s2 << 16) | s1;
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@RET: rts
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; return 1L
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@L0: sta sreg
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sta sreg+1
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lda #1
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; ignore adler
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jmp incsp4
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