; jpegAGA 2.0 utility function written by Günther Röhrich ; this code is Public Domain and may be used with other programs ; this version is for 68020+ processors only ; it is is called from C: ; EncodeHAM8(char *orig, char *yham, int xsize); ; orig = original row in RGBRGB... format ; yham = row in HAM8 chunky format ; xsize = size of row in pixels MACHINE MC68020 ;NOTE: GCC stores all data as 32 bit at subroutine calls! orig EQU 44 ;pointer to original row (RGBRGB) yham EQU 48 ;pointer to actual row (HAM) xsize EQU 52 ;number of pixels XREF _Mult_Table ;address of multiplication table XDEF _EncodeHAM8 ;entry point for function XREF _ColorCache ;an 256K array XREF _ColorTable ;an array with 64 colors * XDEF _blue_left ;only for debugging purposes * XDEF _search_finish ;only for debugging * XDEF _MaxError * XDEF _MaxErrorPos * XDEF _hit ;only for debugging * XDEF _t1 ;only for debugging dseg cnop 0,4 _blue_left: dc.b 0 ;this order is better for HAM-encoding _red_left: dc.b 0 _green_left: dc.b 0,0 ;additional dummy-value for faster longword access cnop 0,2 _offset_orig: dc.w 0 _offset_ham: dc.w 0 _CacheOffset dc.l 0 _colcount dc.w 2 cseg ;register usage: D0 = general purpose register ; D1 = contains afterwards the error ; D2 = orig_blue ; D3 = orig_red ; D4 = orig_green ; D5 = color that should be set ; D6 = offset to actual pixel (HAM) ; D7 = offset for color table / (0,1,2) at HAM ; A0 = best color so far (color+1)*3 ; A1 = pointer to multiplication table ; A2 = pointer to color table / to _blue_left ; A3 = smallest error that has been reached so far ; A4 = used by the Aztec assembler (small data model) ; A5 = pointer to original row (RGBRGB...) ; A6 = pointer to the actual row (HAM) ;computing the difference of color values is done with signed 8 bit ;arithmetic ;the maximum error value is 63^2+63^2+63^2=11907 ;the summation has to be done therefore with 16 bits ;Initializing _EncodeHAM8: movem.l D2-D7/A2-A3/A5/A6,-(A7) ;store registers lea _blue_left,A0 ;load start of left colors lea _ColorTable,A2 move.l (A2),(A0) ;initialize left colors moveq.l #0,D6 ;initialize ham offset move.l yham(sp),A6 move.l orig(sp),A5 lea _Mult_Table,A1 lea 255*2(A1),A1 search_begin: move.b (A5)+,D3 ;load registers with original colors lsr.b #2,D3 move.b (A5)+,D4 ;for faster access lsr.b #2,D4 move.b (A5)+,D2 lsr.b #2,D2 move.w #15000,A3 ;dummy-value for minimum error so far lea _ColorTable,A2 moveq.l #0,D7 ;initialize offset for color table ;find out if the new pixel has the same color as the previous one lea _blue_left,A0 cmp.b (A0),D2 bne.s search_cont cmp.b 1(A0),D3 bne.s search_cont cmp.b 2(A0),D4 bne.s search_cont ;the new pixel has the same color, let's do a special encoding move.w _colcount,D7 move.b 0(A0,D7.w),D5 subq.w #1,_colcount bpl.s ham6_9 move.w #2,_colcount bra.s ham6_9 ;First take a look if we have the value already in the cache search_cont: moveq.l #0,D0 moveq.l #0,D1 move.b D3,D0 ;compute the cache offset lsl.l #6,D0 or.b D4,D0 lsl.l #6,D0 or.b D2,D0 ;now we have the offset in D0 movea.l _ColorCache,A0 ;load start address of the cache move.b 0(A0,D0.l),D1 ;take the value from the cache bne _hit ;jump if we have a cache hit move.l D0,_CacheOffset ;store the offset to avoid recomputing it move.l #3,A0 ;dummy-value for best colornumber so far ; (3 means color 0) search_start: bsr _compute_error cmp.w D1,A3 ;A3 <= D1 ? bls.s search4 move.w D1,A3 ;D1 is smaller than A3, store it move.w D7,A0 ;store color number tst.w D1 ;do we have the correct color ? beq search5 ;then finish immediately search4: cmp.w #64*3,D7 ;have we reached highest colornum ? bne.s search_start ;no, then once again ;A0 contains now (colornumber+1)*3 ;A3 contains the error for that colornumber _t1: move.w A0,D0 movea.l _ColorCache,A2 move.l _CacheOffset,D1 move.b D0,0(A2,D1.l) ;store the value in the cache lea _blue_left,A2 ;restore A2 ;compute the error when using modify mode start_ham6: move.b D2,D0 ;load orig_blue moveq.l #0,D7 ;assume blue should be changed move.b D2,D5 ;store value to change sub.b _blue_left,D0 ;D0=D0-_blue_left bpl.s ham6_1 neg.b D0 ;make result positive ham6_1: move.b D0,D1 ;store maximum error so far move.b D3,D0 ;load orig_red sub.b _red_left,D0 ;D0=D0-_red_left bpl.s ham6_2 neg.b D0 ham6_2: cmp.b D0,D1 ;check D1-D0 bge.s ham6_3 ;jump if D1>=D0 move.b D0,D1 ;store new maximum error moveq.l #1,D7 ;assume red should be changed move.b D3,D5 ;store value to change ham6_3: move.b D4,D0 ;load orig_green sub.b _green_left,D0 ;D0=D0-_green_left bpl.s ham6_4 neg.b D0 ham6_4: cmp.b D0,D1 bge.s ham6_5 move.b D0,D1 ;store maximum error moveq.l #2,D7 ;green should be changed move.b D4,D5 ;store value to change ham6_5: lea _blue_left,A2 move.b D5,0(A2,D7.W) ;perform change ham_error: moveq.l #0,D1 moveq.l #0,D0 move.b D2,D0 ;load blue_origin sub.b (A2)+,D0 ;D0 = blue_color - blue_origin ext.w D0 add.w 0(A1,D0.W*2),D1 move.b D3,D0 ;load red_origin sub.b (A2)+,D0 ;D0 = red_color - red_origin ext.w D0 add.w 0(A1,D0.W*2),D1 move.b D4,D0 ;load green_origin sub.b (A2)+,D0 ;D0 = green_color - green_origin ext.w D0 add.w 0(A1,D0.W*2),D1 cmpa.w D1,A3 ;check what error is smaller bls.s _search_finish ;jump if colortable is better ham6_9: add.b #1,D7 ;needed to get correct code lsl.b #6,D7 ;HAM8-adjust or.b D5,D7 move.b D7,(A6,D6.W) ;store code in bitmap addq.w #1,D6 ;increase _offset_ham cmp.l xsize(sp),D6 ;end of column ? bne search_begin bra.s search_end _search_finish: move.w A0,D0 lea _ColorTable,A2 lea -3(A2,D0.W),A3 ;load A3 with pointer to colors divu #3,D0 subq.w #1,D0 move.b D0,0(A6,D6.W) ;store colornumber in bitmap lea _blue_left,A2 move.l (A3),(A2) addq.w #1,D6 ;increase _offset_ham cmp.l xsize(sp),D6 ;have we reached the end ? bne search_begin search_end: movem.l (A7)+,D2-D7/A2-A3/A5/A6 ;restore registers rts ;jump back to caller ;we jump here if we have reached error 0 by colortable only ;and there was not a cache hit search5: move.w A0,D0 movea.l _ColorCache,A2 move.l _CacheOffset,D1 move.b D0,0(A2,D1.l) ;store the value in the cache bra.s _search_finish ;we jump here if we have a cache hit ;D1 contains the best color number, but we have to compute the error _hit: subq.w #3,D1 ;correct color number move.w D1,D7 bsr.s _compute_error move.w D1,A3 ;D1 is smaller than A3, store it move.w D7,A0 ;store color number bra start_ham6 ;continue with HAM encoding ;compute the error _compute_error: moveq.l #0,D1 moveq.l #0,D0 move.b D2,D0 ;load blue_origin sub.b 0(A2,D7.W),D0 ;D0 = blue_color - blue_origin ext.w D0 ;extend result to word add.w 0(A1,D0.W*2),D1 addq.w #1,D7 ;advance color table offset move.b D3,D0 ;load red_origin sub.b 0(A2,D7.W),D0 ;D0 = red_color - red_origin ext.w D0 add.w 0(A1,D0.W*2),D1 addq.w #1,D7 ;advance color table offset move.b D4,D0 ;load green_origin sub.b 0(A2,D7.W),D0 ;D0 = green_color - green_origin ext.w D0 add.w 0(A1,D0.W*2),D1 ;D1 = D1 + D0*D0 addq.w #1,D7 ;advance color table offset rts