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Título: BitBuster "Extreme" asMSX version Publicado por: pitpan en 29 de Septiembre de 2010, 05:21:39 pm Note: *UNTESTED AS IS*
Código: ;In: HL: source ; DE: destination depack: ;inc hl ;skip original file length ; inc hl ;which is stored in 4 bytes ; inc hl ; inc hl ld a,128 exx ld de,1 exx depack_loop: call getbits jr c,output_compressed ;if set, we got lz77 compression ldi ;copy byte from compressed data to destination [literal byte] jr depack_loop ;handle compressed data output_compressed: ld c,[hl] ;get lowest 7 bits of offset, plus offset extension bit inc hl ;to next byte in compressed data output_match: ld b,0 bit 7,c jr z,output_match1 ;no need to get extra bits if carry not set call getbits call rlbgetbits call rlbgetbits call rlbgetbits jr c,output_match1 ;since extension mark already makes bit 7 set res 7,c ;only clear it if the bit should be cleared output_match1: inc bc ;return a gamma-encoded value ;length returned in HL exx ;to second register set! ld h,d ld l,e ;initial length to 1 ld b,e ;bitcount to 1 ;determine number of bits used to encode value get_gamma_value_size: exx call getbits exx jr nc,get_gamma_value_size_end ;if bit not set, bitlength of remaining is known inc b ;increase bitcount jr get_gamma_value_size ;repeat... get_gamma_value_bits: exx call getbits exx adc hl,hl ;insert new bit in HL get_gamma_value_size_end: djnz get_gamma_value_bits ;repeat if more bits to go get_gamma_value_end: inc hl ;length was stored as length-2 so correct this exx ;back to normal register set ret c ;HL' = length push hl ;address compressed data on stack exx push hl ;match length on stack exx ld h,d ld l,e ;destination address in HL... sbc hl,bc ;calculate source address pop bc ;match length from stack ldir ;transfer data pop hl ;address compressed data back from stack jr depack_loop rlbgetbits: rl b getbits: add a,a ret nz ld a,[hl] inc hl rla ret |