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If it ain't Lisp, it's crap

Name: Anonymous 2012-06-24 22:04

Lisp

(defun png-defilter (g s)
  (let* ((w (gfx-w g))
         (h (gfx-h g))
         (c (gfx-c g))
         (s (cons s 0))
         (l (* w c))
         (d (cons (vec (* h l) u1) 0)))
    (dotimes (y h)
      (let* ((f (q s))
             (p  (cons (car d) (cdr d)))  ; prev pixel
             (u  (cons (car d) (- (cdr d) l)))  ; upper row
             (pu (cons (car u) (cdr u)))) ; upper row, prev pixel
        (when (and (= y 0) (case f ((2 3 4) t)))
          (setf p (cons (vec l u1) 0)))
        (case f
          (0 (dotimes (_ l)       (q d (q s)))) ; plaintext
          (1 (dotimes (_ c)       (q d (q s))) ; sub
             (dotimes (_ (- l c)) (q d (+ (q p) (q s)))))
          (2 (dotimes (_ l)       (q d (+ (q u) (q s))))) ; up
          (3 (dotimes (_ c)       (q d (+ (avg     0 (q u)) (q s)))) ; average
             (dotimes (_ (- l c)) (q d (+ (avg (q p) (q u)) (q s)))))
          (4 (dotimes (_ c)       (q d (+ (paeth     0 (q u)      0) (q s)))) ; paeth
             (dotimes (_ (- l c)) (q d (+ (paeth (q p) (q u) (q pu)) (q s)))))
          (otherwise (gfx-load-error "Invalid line filter (~a)" f)))))
    (setf (gfx-d g) (rgb-to-ints c 1 (car d)))))


C/C++

static unsigned unfilterScanline(unsigned char* recon, const unsigned char* scanline, const unsigned char* precon,
                                 size_t bytewidth, unsigned char filterType, size_t length)
{
  /*
  For PNG filter method 0
  unfilter a PNG image scanline by scanline. when the pixels are smaller than 1 byte,
  the filter works byte per byte (bytewidth = 1)
  precon is the previous unfiltered scanline, recon the result, scanline the current one
  the incoming scanlines do NOT include the filtertype byte, that one is given in the parameter filterType instead
  recon and scanline MAY be the same memory address! precon must be disjoint.
  */

  size_t i;
  switch(filterType)
  {
    case 0:
      for(i = 0; i < length; i++) recon[i] = scanline[i];
      break;
    case 1:
      for(i =         0; i < bytewidth; i++) recon[i] = scanline[i];
      for(i = bytewidth; i <    length; i++) recon[i] = scanline[i] + recon[i - bytewidth];
      break;
    case 2:
      if(precon)
      {
        for(i = 0; i < length; i++) recon[i] = scanline[i] + precon[i];
      }
      else
      {
        for(i = 0; i < length; i++) recon[i] = scanline[i];
      }
      break;
    case 3:
      if(precon)
      {
        for(i =         0; i < bytewidth; i++) recon[i] = scanline[i] + precon[i] / 2;
        for(i = bytewidth; i <    length; i++) recon[i] = scanline[i] + ((recon[i - bytewidth] + precon[i]) / 2);
      }
      else
      {
        for(i =         0; i < bytewidth; i++) recon[i] = scanline[i];
        for(i = bytewidth; i <    length; i++) recon[i] = scanline[i] + recon[i - bytewidth] / 2;
      }
      break;
    case 4:
      if(precon)
      {
        for(i = 0; i < bytewidth; i++)
        {
          recon[i] = (scanline[i] + precon[i]); /*paethPredictor(0, precon[i], 0) is always precon[i]*/
        }
        for(i = bytewidth; i < length; i++)
        {
          recon[i] = (scanline[i] + paethPredictor(recon[i - bytewidth], precon[i], precon[i - bytewidth]));
        }
      }
      else
      {
        for(i = 0; i < bytewidth; i++)
        {
          recon[i] = scanline[i];
        }
        for(i = bytewidth; i < length; i++)
        {
          /*paethPredictor(recon[i - bytewidth], 0, 0) is always recon[i - bytewidth]*/
          recon[i] = (scanline[i] + recon[i - bytewidth]);
        }
      }
      break;
    default: return 36; /*error: unexisting filter type given*/
  }
  return 0;
}

static unsigned unfilter(unsigned char* out, const unsigned char* in, unsigned w, unsigned h, unsigned bpp)
{
  /*
  For PNG filter method 0
  this function unfilters a single image (e.g. without interlacing this is called once, with Adam7 seven times)
  out must have enough bytes allocated already, in must have the scanlines + 1 filtertype byte per scanline
  w and h are image dimensions or dimensions of reduced image, bpp is bits per pixel
  in and out are allowed to be the same memory address (but aren't the same size since in has the extra filter bytes)
  */

  unsigned y;
  unsigned char* prevline = 0;

  /*bytewidth is used for filtering, is 1 when bpp < 8, number of bytes per pixel otherwise*/
  size_t bytewidth = (bpp + 7) / 8;
  size_t linebytes = (w * bpp + 7) / 8;

  for(y = 0; y < h; y++)
  {
    size_t outindex = linebytes * y;
    size_t inindex = (1 + linebytes) * y; /*the extra filterbyte added to each row*/
    unsigned char filterType = in[inindex];

    unsigned error = unfilterScanline(&out[outindex], &in[inindex + 1], prevline, bytewidth, filterType, linebytes);
    if(error) return error;

    prevline = &out[outindex];
  }

  return 0;
}

Name: Anonymous 2012-06-24 22:27

I like the latter version.  It has comments.

Name: Anonymous 2012-06-24 23:20

I'm with >>2
maybe if the lisp code were commented it'd be a bit better

it does look nice though

Name: Anonymous 2012-06-25 0:15

>>3
I think all it needs is more obvious variable names. Granted this would make the lines longer, and with lisp, it becomes harder to read the syntax when the names are long. And it isn't fun to reason about code that uses cons as a generic data structure, but this is short enough to be ok.

Name: Anonymous 2012-06-25 1:14

LOC does not determine code quality.

Name: Anonymous 2012-06-25 3:55

>>5
yes it does.

signed,
an exhausted C++ programmer.

Name: Anonymous 2012-06-25 5:28

>>4
uses cons as a generic data structure
are there other way to create a pointer to array? I think compiler will optimize CONS on stack.

Name: Anonymous 2012-06-25 6:06

#define _albanian(a, b) a ## b
#define albanian(a, b) _albanian(a, b)
#define sausage print
#define shape f
#define strnig(x) #x
#define strjew ","
#define strchink " "

int main()
{
  albanian(sausage, shape)(strnig(Hello) strjew strchink strnig(world!));
  return 0;
}

Name: Anonymous 2012-06-25 6:06

>>7
it would have to be a really smart compiler

Name: Anonymous 2012-06-25 6:10

Common Lisp has symbols. SEPPLES has abominations like http://www.humus.name/index.php?ID=296.

Name: Anonymous 2012-06-25 6:14

try using C, the preprocessor and K&R style next time

Name: Anonymous 2012-06-25 8:50

>>10
Has he never heard of templates?

Name: Anonymous 2012-06-25 9:28

>>10
what if compiler changes?

Name: Anonymous 2012-06-25 10:33

>>11
why not use an enum?

Name: Anonymous 2012-06-25 11:39

Damn. When I need universally unique identifiers for objects in a program, I use universally unique identifiers...

Name: Anonymous 2012-06-25 12:16

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Name: Anonymous 2012-06-25 12:33

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Name: Anonymous 2012-06-25 12:47

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Name: Anonymous 2012-06-25 12:50

>>15
Yes. But languages like C/C++ are trying to convince you, that you dont actually need universally unique identifiers.

It's like communism: when North Korean people say they need this and that, commies respond that people dont really need this or that, and can survive even on grass diet.

This approach was invented to lower consumption by educating people that wanting nourishing breakfast is irrational and bourgeois.

Name: bampu pantsu 2012-06-26 3:00

bampu pantsu
Don't change these.
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