MULPIX D,{#}S Syntax question

Bob Drury

if D=d4d3d2d1 and S =s3s2s1s0 then Multipy DxS by should be d3=d3s3 d2=d2s2 d1=d1s1 d0=d0s0
but that doeesn' happen and the nomenclature $FF = 1.0 and $00= 0.0 I am not sure what that means

the ADDPIx d3= d3+s3 d2=d2+s2 d1= d1+s1 d0 = d0+s0 works so not sure what MULPIX is doing

Regards
Bob (WRD)

AJL

What result are you expecting, and what are you seeing?

From the instruction description, with $FF = 1.0 and $00 = 0.0 then with D of $0080FFFF and S of $008080FF I would expect a result of something like $004080FF.

That’s:
$00 x $00 = 0.0 x 0.0 = 0.0 = $00
$80 x $80 = 0.5 x 0.5 = 0.25 = $40
$80 x $FF = 0,5 x 1.0 = 0.5 = $80
$FF x $FF = 1.0 x 1.0 = 1.0 = $FF

I’m not in a position to test my interpretation.

Bob Drury

AJL
Will test.
Thanks
Bob (WRD)

Ariba

It's multiplying with scaling, maybe SCLPIX, or SCAPIX would have been a better name.
So if D=d3d2d1d0 and S=s3s2s1s0 the result should be:

  d3 = d3*s3/255
  d2 = d2*s2/255
  d1 = d1*s1/255
  d0 = d0*s0/255

Andy

Bob Drury

AJL
Tested and you are correct. Thanks
Ariba
I will modify notes about scaling and rounding to bit
Regards
Bob (WRD)

AJL

Glad to be of assistance :-)

JonnyMac

I didn't know about mulpix, and I'm glad you pointed it out. I had this routine in my pixel driver which is a direct port from the P1.

pub colorx(r, g, b, w, level) : result | m

'' Packs r-g-b-w bytes into long
'' -- r, g, b, and w are element levels, 0..255
'' -- level is brightness, 0..255 (0..100%)

  if (level <= 0)
    result := $00_00_00_00

  elseif (level >= 255)
    result := color(r, g, b, w)

  else
    r := r * level / 255                                        ' apply level to rgbw
    g := g * level / 255
    b := b * level / 255
    w := w * level / 255
    result := color(r, g, b, w)

I upgraded the method in my P2 object to this, and save a little more than 9 microseconds at 200MHz.

pub p2_colorx(r, g, b, w, level) : result 

'' Packs r-g-b-w bytes into long
'' -- r, g, b, and w are element levels, 0..255
'' -- level is brightness, 0..255 (0..100%)

  org
                cmps      level, #0                     wcz     ' at or below 0?
    if_be       jmp       #.done                                '  yes, done

                setbyte   result, r, #3                         ' make 32-bit color
                setbyte   result, g, #2
                setbyte   result, b, #1
                setbyte   result, w, #0

                cmps      level, #255                   wcz     ' at or above 255?
    if_ae       jmp       #.done                                '  yes, done

                rep       #1, #3                                ' make multiplier
                 rolbyte  level, level, #0

                mulpix    result, level                         ' scale the color

.done
  end

Wuerfel_21

                rep       #1, #3                                ' make multiplier
                 rolbyte  level, level, #0

You can do this to the same effect:

                 movbyts level, #%%0000

---

Or, alternatively, instead of

                 movbyts level, #%%0000
                 mulpix result,level

you can use

                 setpiv level
                 blnpix result,#0

JonnyMac

Thank you!