2016-03-01 15:47:10 +00:00
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README - DOOM assembly code
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Okay, I add the DOS assembly module for the historically
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inclined here (may rec.games.programmer suffer). If anyone
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feels the urge to port these to GNU GCC; either inline or
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as separate modules including Makefile support, be my guest.
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Module tmap.S includes the inner loops for texture mapping,
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the interesting one being the floor/ceiling span rendering.
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There was another module in the source dump, fpfunc.S, that
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had both texture mapping and fixed point functions. It
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contained implementations both for i386 and M68k. For
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brevity, I include only the i386 fixed point stuff below.
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//====================================================
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// tmap.S as of January 10th, 1997
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//================
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//
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// R_DrawColumn
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//
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//================
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.data
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loopcount .long 0
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pixelcount .long 0
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.text
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.align 16
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.globl _R_DrawColumn
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_R_DrawColumn:
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pushad
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movl ebp,[_dc_yl]
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movl ebx,ebp
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movl edi,[_ylookup+ebx*4]
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movl ebx,[_dc_x]
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addl edi,[_columnofs + ebx*4]
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movl eax,[_dc_yh]
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incl eax
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subl eax,ebp // pixel count
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movl [pixelcount],eax // save for final pixel
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js done // nothing to scale
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shrl eax,1 // double pixel count
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movl [loopcount],eax
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movl ecx,[_dc_iscale]
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movl eax,[_centery]
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subl eax,ebp
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imull ecx
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movl ebp,[_dc_texturemid]
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subl ebp,eax
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shll ebp,9 // 7 significant bits, 25 frac
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movl esi,[_dc_source]
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movl ebx,[_dc_iscale]
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shll ebx,9
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movl eax,OFFSET patch1+2 // convice tasm to modify code...
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movl [eax],ebx
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movl eax,OFFSET patch2+2 // convice tasm to modify code...
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movl [eax],ebx
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// eax aligned colormap
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// ebx aligned colormap
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// ecx,edx scratch
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// esi virtual source
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// edi moving destination pointer
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// ebp frac
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movl ecx,ebp // begin calculating first pixel
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addl ebp,ebx // advance frac pointer
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shrl ecx,25 // finish calculation for first pixel
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movl edx,ebp // begin calculating second pixel
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addl ebp,ebx // advance frac pointer
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shrl edx,25 // finish calculation for second pixel
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movl eax,[_dc_colormap]
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movl ebx,eax
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movb al,[esi+ecx] // get first pixel
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movb bl,[esi+edx] // get second pixel
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movb al,[eax] // color translate first pixel
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movb bl,[ebx] // color translate second pixel
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testl [pixelcount],0fffffffeh
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jnz doubleloop // at least two pixels to map
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jmp checklast
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.align 16
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doubleloop:
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movl ecx,ebp // begin calculating third pixel
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patch1:
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addl ebp,12345678h // advance frac pointer
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movb [edi],al // write first pixel
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shrl ecx,25 // finish calculation for third pixel
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movl edx,ebp // begin calculating fourth pixel
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patch2:
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addl ebp,12345678h // advance frac pointer
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movl [edi+SCREENWIDTH],bl // write second pixel
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shrl edx,25 // finish calculation for fourth pixel
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movb al,[esi+ecx] // get third pixel
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addl edi,SCREENWIDTH*2 // advance to third pixel destination
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movb bl,[esi+edx] // get fourth pixel
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decl [loopcount] // done with loop?
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movb al,[eax] // color translate third pixel
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movb bl,[ebx] // color translate fourth pixel
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jnz doubleloop
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// check for final pixel
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checklast:
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testl [pixelcount],1
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jz done
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movb [edi],al // write final pixel
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done:
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popad
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ret
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//================
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//
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// R_DrawSpan
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//
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// Horizontal texture mapping
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//
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//================
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.align 16
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.globl _R_DrawSpan
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_R_DrawSpan:
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pushad
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//
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// find loop count
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//
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movl eax,[_ds_x2]
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incl eax
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subl eax,[_ds_x1] // pixel count
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movl [pixelcount],eax // save for final pixel
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js hdone // nothing to scale
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shrl eax,1 // double pixel count
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movl [loopcount],eax
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//
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// build composite position
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//
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movl ebp,[_ds_xfrac]
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shll ebp,10
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andl ebp,0ffff0000h
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movl eax,[_ds_yfrac]
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shrl eax,6
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andl eax,0ffffh
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orl ebp,eax
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movl esi,[_ds_source]
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//
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// calculate screen dest
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//
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movl edi,[_ds_y]
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movl edi,[_ylookup+edi*4]
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movl eax,[_ds_x1]
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addl edi,[_columnofs+eax*4]
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//
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// build composite step
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//
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movl ebx,[_ds_xstep]
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shll ebx,10
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andl ebx,0ffff0000h
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movl eax,[_ds_ystep]
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shrl eax,6
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andl eax,0ffffh
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orl ebx,eax
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movl eax,OFFSET hpatch1+2 // convice tasm to modify code...
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movl [eax],ebx
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movl eax,OFFSET hpatch2+2 // convice tasm to modify code...
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movl [eax],ebx
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// eax aligned colormap
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// ebx aligned colormap
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// ecx,edx scratch
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// esi virtual source
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// edi moving destination pointer
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// ebp frac
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shldl ecx,ebp,22 // begin calculating third pixel (y units)
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shldl ecx,ebp,6 // begin calculating third pixel (x units)
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addl ebp,ebx // advance frac pointer
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andl ecx,4095 // finish calculation for third pixel
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shldl edx,ebp,22 // begin calculating fourth pixel (y units)
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shldl edx,ebp,6 // begin calculating fourth pixel (x units)
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addl ebp,ebx // advance frac pointer
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andl edx,4095 // finish calculation for fourth pixel
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movl eax,[_ds_colormap]
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movl ebx,eax
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movb al,[esi+ecx] // get first pixel
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movb bl,[esi+edx] // get second pixel
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movb al,[eax] // color translate first pixel
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movb bl,[ebx] // color translate second pixel
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testl [pixelcount],0fffffffeh
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jnz hdoubleloop // at least two pixels to map
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jmp hchecklast
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.align 16
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hdoubleloop:
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shldl ecx,ebp,22 // begin calculating third pixel (y units)
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shldl ecx,ebp,6 // begin calculating third pixel (x units)
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hpatch1:
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addl ebp,12345678h // advance frac pointer
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movb [edi],al // write first pixel
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andl ecx,4095 // finish calculation for third pixel
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shldl edx,ebp,22 // begin calculating fourth pixel (y units)
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shldl edx,ebp,6 // begin calculating fourth pixel (x units)
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hpatch2:
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addl ebp,12345678h // advance frac pointer
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movb [edi+1],bl // write second pixel
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andl edx,4095 // finish calculation for fourth pixel
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movb al,[esi+ecx] // get third pixel
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addl edi,2 // advance to third pixel destination
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movb bl,[esi+edx] // get fourth pixel
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decl [loopcount] // done with loop?
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movb al,[eax] // color translate third pixel
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movb bl,[ebx] // color translate fourth pixel
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jnz hdoubleloop
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// check for final pixel
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hchecklast:
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testl [pixelcount],1
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jz hdone
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movb [edi],al // write final pixel
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hdone:
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popad
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ret
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//====================================================
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// fpfunc.S as of January 10th, 1997 (parts)
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#ifdef i386
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.text
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.align 4
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.globl _FixedMul
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_FixedMul:
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pushl %ebp
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movl %esp,%ebp
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movl 8(%ebp),%eax
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imull 12(%ebp)
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shrdl $16,%edx,%eax
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popl %ebp
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ret
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.align 4
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.globl _FixedDiv2
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_FixedDiv2:
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pushl %ebp
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movl %esp,%ebp
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movl 8(%ebp),%eax
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cdq
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shldl $16,%eax,%edx
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sall $16,%eax
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idivl 12(%ebp)
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popl %ebp
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ret
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#endif
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