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135 lines
2.8 KiB
ArmAsm
135 lines
2.8 KiB
ArmAsm
;
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; Piotr Fusik, 14.11.2001
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;
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; unsigned long __fastcall__ crc32 (unsigned long crc, unsigned char* buf,
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; unsigned len);
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;
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.export _crc32
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.import compleax, incsp2, incsp4, popax, popeax
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.importzp sreg, ptr1, ptr2, tmp1, tmp2
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POLYNOMIAL = $EDB88320
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make_table:
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ldx #0
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@L1: lda #0
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sta tmp2
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sta sreg
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sta sreg+1
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ldy #8
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txa
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@L2: sta tmp1
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lsr a
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bcc @L3
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lda sreg+1
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lsr a
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eor #(POLYNOMIAL>>24)&$FF
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sta sreg+1
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lda sreg
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ror a
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eor #(POLYNOMIAL>>16)&$FF
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sta sreg
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lda tmp2
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ror a
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eor #(POLYNOMIAL>>8)&$FF
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sta tmp2
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lda tmp1
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ror a
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eor #POLYNOMIAL&$FF
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bcs @L4 ; branch always
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@L3: rol a
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lsr sreg+1
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ror sreg
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ror tmp2
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ror a
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@L4: dey
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bne @L2
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sta table_0,x
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lda tmp2
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sta table_1,x
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lda sreg
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sta table_2,x
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lda sreg+1
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sta table_3,x
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inx
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bne @L1
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inc table_initialised
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RET:
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rts
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_crc32:
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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 0;
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ora ptr1+1
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beq @L0
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; if (!tables_initialised) make_tables();
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lda table_initialised
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bne @dont_make
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jsr make_table
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@dont_make:
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; eax = crc
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jsr popeax
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; if (len == 0) return crc;
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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:
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; eax = ~crc
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jsr compleax
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stx tmp2
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ldy #0
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; crc = (crc >> 8) ^ table[(crc & 0xff) ^ *p++];
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@L3: eor (ptr1),y
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tax
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lda table_0,x
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eor tmp2
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sta tmp1
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lda table_1,x
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eor sreg
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sta tmp2
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lda table_2,x
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eor sreg+1
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sta sreg
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lda table_3,x
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sta sreg+1
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lda tmp1
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iny
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bne @L4
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inc ptr1+1
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@L4: 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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ldx tmp2
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jmp compleax
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; return 0L
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@L0: sta sreg
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sta sreg+1
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; ignore crc
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jmp incsp4
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.data
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table_initialised:
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.byte 0
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.bss
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table_0: .res 256
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table_1: .res 256
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table_2: .res 256
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table_3: .res 256
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