gistfile1.txt

int generate_indexed_something(size_t BufPixels, xxx ResultArray, xxx pixels, int_t pixlen)
{
    PyObject * BufString = 0;
    PyObject * Result = 0;

    /* extend ResultArray by a bunch of converted pixels at a time */
    if (BufPixels % 4 != 0)
    {
      /* fill out unused part of byte with zeroes--actually shouldn't occur */
      PixBuf[BufPixels / 4] &= ~(0xff << BufPixels % 4 * 2);
    }

    BufString = PyString_FromStringAndSize((const char *)PixBuf, (BufPixels + 3) / 4);
    if (BufString == 0)
      goto cleanup;
    
    Result = PyObject_CallMethod(ResultArray, "fromstring", "O", BufString);
    if (Result == 0)
      goto cleanup;
        
cleanup:
    Py_XDECREF(Result);
    Py_XDECREF(BufString);  

    return PyErr_Occurred();
}

void do_something()
{
  /* generate indexed version of image */
  const size_t PixBufSize = 128 /* convenient buffer size to avoid heap allocation */;
  const size_t MaxPixels = PixBufSize * 4; /* 2 bits per pixel */
  uint8_t PixBuf[PixBufSize];
  size_t BufPixels;
  int_t pixlen = nrpixels;

  ResultArray = PyObject_CallMethod(ArrayModule, "array", "s", "B");
  if (ResultArray == 0)
      goto cleanup;

  pixels = (const uint32_t *)pixaddr;
  BufPixels = 0;
  for(pixlen = nrpixels; pixlen>=0 && BufPixels !=0; --pixlen)
  {
      if (generate_indexed_something(BufPixels, pixels, pixlen))
        goto cleanup;
      
      const uint32_t thispixel = *pixels;
      for (histindex = 0; histogram[histindex].pixel != thispixel; ++histindex)
          /* guaranteed to find pixel index */;

      if (BufPixels % 4 == 0)
      {
        /* starting new byte */
        PixBuf[BufPixels / 4] = 0; /* ensure there's no junk in it */
      }
      
      PixBuf[BufPixels / 4] |= histogram[histindex].index << BufPixels % 4 * 2;
      ++BufPixels;
      ++pixels;
  }

  cleanup:
    Py_XDECREF(ResultArray);  
}