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287 lines
4.8 KiB
ArmAsm
287 lines
4.8 KiB
ArmAsm
;
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; Lauri Kasanen, 6 Jun 2017
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; (C) Mega Cat Studios
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; An optimized LZ4 decompressor
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;
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; Almost 7 times faster, uses no RAM (vs 14 bytes BSS), and takes 1/4 the space
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; vs the official C source.
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;
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.importzp sp, sreg, regsave, regbank
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.importzp tmp1, tmp2, tmp3, tmp4, ptr1, ptr2, ptr3, ptr4
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.macpack longbranch
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.import memcpy_upwards,pushax,popax
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.export _decompress_lz4
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out = regsave
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written = regsave + 2
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tmp = tmp1
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token = tmp2
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offset = ptr3
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in = sreg
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outlen = ptr4
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; ---------------------------------------------------------------
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; void decompress_lz4 (const u8 *in, u8 * const out, const u16 outlen)
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; ---------------------------------------------------------------
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.segment "CODE"
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.proc _decompress_lz4: near
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sta outlen
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stx outlen+1
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jsr popax
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sta out
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stx out+1
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jsr popax
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sta in
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stx in+1
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;
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; written = 0;
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;
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lda #$00
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sta written
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;
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; while (written < outlen) {
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;
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jmp L0046
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;
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; token = *in++;
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;
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L0004: ldy #$00
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lda (in),y
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sta token
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inc in
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bne L000A
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inc in+1
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L000A:
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;
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; offset = token >> 4;
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;
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ldx #$00
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lsr a
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lsr a
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lsr a
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lsr a
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sta offset
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stx offset+1
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;
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; token &= 0xf;
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; token += 4; // Minmatch
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;
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lda token
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and #$0F
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clc
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adc #$04
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sta token
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;
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; if (offset == 15) {
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;
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lda offset
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cmp #$0F
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L0013: bne L001A
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;
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; tmp = *in++;
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;
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ldy #$00
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lda (in),y
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sta tmp
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inc in
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bne L0017
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inc in+1
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L0017:
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;
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; offset += tmp;
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;
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clc
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adc offset
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sta offset
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lda #$00
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adc offset+1
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sta offset+1
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;
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; if (tmp == 255)
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;
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lda tmp
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cmp #$FF
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;
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; goto moreliterals;
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;
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jmp L0013
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;
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; if (offset) {
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;
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L001A: lda offset
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ora offset+1
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beq L001C
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;
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; memcpy(&out[written], in, offset);
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;
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lda out
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clc
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adc written
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sta ptr2
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lda out+1
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adc written+1
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tax
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lda ptr2
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stx ptr2+1
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jsr pushax
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lda in
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ldx in+1
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sta ptr1
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stx ptr1+1
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; ldy #$00 - not needed as pushax zeroes Y
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jsr memcpy_upwards
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;
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; written += offset;
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;
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lda offset
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clc
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adc written
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sta written
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lda offset+1
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adc written+1
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sta written+1
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;
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; in += offset;
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;
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lda offset
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clc
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adc in
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sta in
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lda offset+1
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adc in+1
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sta in+1
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;
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; if (written >= outlen)
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;
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L001C: lda written
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cmp outlen
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lda written+1
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sbc outlen+1
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;
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; return;
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;
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bcc L0047
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rts
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;
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; memcpy(&offset, in, 2);
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;
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L0047: ldy #$00
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lda (in),y
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sta offset
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iny
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lda (in),y
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sta offset+1
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;
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; in += 2;
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;
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lda #$02
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clc
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adc in
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sta in
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bcc L002F
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inc in+1
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;
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; copysrc = out + written - offset;
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;
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L002F: lda out
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clc
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adc written
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tay
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lda out+1
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adc written+1
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tax
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tya
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sec
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sbc offset
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sta ptr1
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txa
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sbc offset+1
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sta ptr1+1
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;
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; offset = token;
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;
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lda #$00
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sta offset+1
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lda token
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sta offset
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;
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; if (token == 19) {
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;
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cmp #$13
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L0045: bne L003C
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;
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; tmp = *in++;
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;
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ldy #$00
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lda (in),y
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sta tmp
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inc in
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bne L0039
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inc in+1
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L0039:
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;
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; offset += tmp;
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;
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clc
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adc offset
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sta offset
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tya
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adc offset+1
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sta offset+1
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;
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; if (tmp == 255)
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;
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lda tmp
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cmp #$FF
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;
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; goto morematches;
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;
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jmp L0045
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;
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; memcpy(&out[written], copysrc, offset);
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;
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L003C: lda out
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clc
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adc written
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sta ptr2
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lda out+1
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adc written+1
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tax
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lda ptr2
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stx ptr2+1
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jsr pushax
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jsr memcpy_upwards
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;
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; written += offset;
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;
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lda offset
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clc
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adc written
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sta written
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lda offset+1
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adc written+1
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L0046: sta written+1
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;
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; while (written < outlen) {
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;
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lda written
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cmp outlen
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lda written+1
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sbc outlen+1
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jcc L0004
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rts
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.endproc
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