Skip to content
Branch: master
Find file Copy path
Find file Copy path
Fetching contributors…
Cannot retrieve contributors at this time
237 lines (205 sloc) 6.06 KB
/** FC8 compression by Steve Chamberlin* Derived from liblzg by Marcus Geelnard* 68000 decompressor by Steve Chamberlin*/#define FC8_DECODED_SIZE_OFFSET 4#define FC8_HEADER_SIZE 8//-------------------------------------------------------------------------------// fc8_decode - Decode a compressed memory block// a0 = in buffer// a1 = out buffer// d1 = outsize// d0 = result (1 if decompression was successful, or 0 upon failure)//-------------------------------------------------------------------------------#pragma parameter __D0 fc8_decode(__A0, __A1, __D1)asm unsigned short fc8_decode(unsigned char* in, unsigned char* out, unsigned long outsize){ machine 68020 movem.l d1-d7/a0-a6,-(sp) bra _Init_Decode// lookup table for decoding the copy length-1 parameter_FC8_LENGTH_DECODE_LUT: dc.b 2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17 dc.b 18,19,20,21,22,23,24,25,26,27,28,34,47,71,127,255//-------------------------------------------------------------------------------// _GetUINT32 - alignment independent reader for 32-bit integers// a0 = in// d6 = offset// d7 = result//-------------------------------------------------------------------------------_GetUINT32: move.b (a0,d6.w),d7 asl.w #8,d7 move.b 1(a0,d6.w),d7 swap d7 move.b 2(a0,d6.w),d7 asl.w #8,d7 move.b 3(a0,d6.w),d7 rts _Init_Decode: // check magic ID cmp.b #'F',(a0) bne _fail cmp.b #'C',1(a0) bne _fail cmp.b #'8',2(a0) bne _fail cmp.b #'_',3(a0) bne _fail // check decoded size - enough space in the output buffer? moveq #FC8_DECODED_SIZE_OFFSET,d6 bsr.s _GetUINT32 cmp.l d7,d1 bhi _fail // advance a0 to start of compressed data lea FC8_HEADER_SIZE(a0), a0 // a5 = base of length decode lookup table //lea _FC8_LENGTH_DECODE_LUT(pc),a5 lea -110(pc),a5 // fix PC offset manually after assembly // helpful constants move.l #0x0000001F, d1 move.l #0x00000007, d2 move.l #0x00000001, d3 move.l #0x0000003F, d4 // Main decompression loop_mainloop: move.b (a0)+, d6 // d6 = next token bmi.s _BR1_BR2 // BR1 and BR2 tokens have the high bit set btst #6, d6 // check bit 6 to see if this is a BR0 or LIT token bne.s _BR0// LIT 00aaaaaa - copy literal string of aaaaaa+1 bytes from input to output _LIT: move.l a0, a4 // a4 = source ptr for copy and.w d4, d6 // AND with 0x3F, d6 = length-1 word for copy lea 1(a0,d6.w), a0 // advance a0 to the end of the literal string bra.s _copyLoop // BR0 01baaaaa - copy b+3 bytes from output backref aaaaa to output_BR0: move.b d6, d5 and.l d1, d5 // AND with 0x1F, d5 = offset for copy = (long)(t0 & 0x1F) beq _done // BR0 with 0 offset means EOF move.l a1, a4 sub.l d5, a4 // a4 = source ptr for copy move.b (a4)+, (a1)+ // copy 3 bytes, can't use move.w. or move.l because src and dest may overlap move.b (a4)+, (a1)+ move.b (a4)+, (a1)+ btst #5, d6 // check b bit beq.s _mainloop move.b (a4)+, (a1)+ // copy 1 more byte bra.s _mainloop _BR1_BR2: btst #6, d6 // check bit 6 to see if this is a BR1 or BR2 token bne.s _BR2// BR1 10bbbaaa'aaaaaaaa - copy bbb+3 bytes from output backref aaa'aaaaaaaa to output_BR1: move.b d6,d5 and.l d2, d5 // AND with 0x07 lsl.l #8, d5 move.b (a0)+, d5 // d5 = offset for copy = ((long)(t0 & 0x07) << 8) | t1 lsr.b #3, d6 and.w d2, d6 // AND with 0x07 addq.w #2, d6 // d6 = length-1 word for copy = ((word)(t0 >> 3) & 0x7) + 1 bra.s _copyBackref// BR2 11bbbbba'aaaaaaaa'aaaaaaaa - copy lookup_table[bbbbb] bytes from output backref a'aaaaaaaa'aaaaaaaa to output_BR2: move.b d6,d5 and.w d3, d5 // AND with 0x01 swap d5 move.w (a0)+, d5 // d5 = offset for copy = ((long)(t0 & 0x01) << 16) | (t1 << 8) | t2 lsr.b #1, d6 and.w d1, d6 // AND with 0x1F move.b (a5,d6.w),d6 // d6 = length-1 word for copy = ((word)(t0 >> 3) & 0x7) + 1 // fall through to _copyBackref // copy data from a previous location in the output buffer // d5 = offset from current buffer position _copyBackref: move.l a1, a4 sub.l d5, a4 // a4 = source ptr for copy cmpi.l #4, d5 blt.s _nearCopy // must copy byte-by-byte if offset < 4, to avoid overlapping long copies // Partially unrolled block copy. Requires 68020 or better. // Uses move.l and move.w where possible, even though both source and dest may be unaligned. // It's still faster than multiple move.b instructions // d6 = length-1_copyLoop: cmpi.w #16, d6 bge.s _copy17orMore jmp _copy16orFewer(d6.w*2)_copy16orFewer: bra.s _copy1 bra.s _copy2 bra.s _copy3 bra.s _copy4 bra.s _copy5 bra.s _copy6 bra.s _copy7 bra.s _copy8 bra.s _copy9 bra.s _copy10 bra.s _copy11 bra.s _copy12 bra.s _copy13 bra.s _copy14 bra.s _copy15 bra.s _copy16_copy15: move.l (a4)+, (a1)+_copy11: move.l (a4)+, (a1)+ _copy7: move.l (a4)+, (a1)+_copy3: move.w (a4)+, (a1)+_copy1: move.b (a4)+, (a1)+ bra _mainloop_copy14: move.l (a4)+, (a1)+_copy10: move.l (a4)+, (a1)+_copy6: move.l (a4)+, (a1)+_copy2: move.w (a4)+, (a1)+ bra _mainloop_copy13: move.l (a4)+, (a1)+_copy9: move.l (a4)+, (a1)+_copy5: move.l (a4)+, (a1)+ move.b (a4)+, (a1)+ bra _mainloop_copy16: move.l (a4)+, (a1)+_copy12: move.l (a4)+, (a1)+_copy8: move.l (a4)+, (a1)+_copy4: move.l (a4)+, (a1)+ bra _mainloop_copy17orMore: move.l (a4)+, (a1)+ move.l (a4)+, (a1)+ move.l (a4)+, (a1)+ move.l (a4)+, (a1)+ subi.w #16, d6 cmpi.w #16, d6 bge.s _copy17orMore jmp _copy16orFewer(d6.w*2) _nearCopy: cmpi.l #1,d5 beq.s _copyRLE _nearLoop: move.b (a4)+, (a1)+ dbf d6, _nearLoop bra _mainloop_copyRLE: // assumes length is at least 3 move.b (a4), (a1)+ // copy first byte btst #0, d6 beq.s _doRLE // branch if copy length is odd (because d6 is length-1) move.b (a4), (a1)+ // copy second byte_doRLE: subq.w #2, d6 lsr.w #1, d6 // length = (length-2) / 2 move.w (a4), d5 _rleLoop: move.w d5, (a1)+ dbf d6, _rleLoop bra _mainloop_fail: moveq.w #0, d0 // result = 0 bra _exit _done: moveq.w #1, d0 // result = 1 _exit: movem.l (sp)+, d1-d7/a0-a6 rts}
You can’t perform that action at this time.