Get rid of the additional loop of reversing the order of rows

...we can do this by correcting the addressing in the resulting buffer filling
loops so that the image rows end up in the right place from the beginning

Author: victoryforce

src/imageio/imageio_pfm.c

@@ -99,7 +99,7 @@ DT_OMP_FOR(collapse(2))
         dt_aligned_pixel_t pix = {0.0f, 0.0f, 0.0f, 0.0f};
         for_three_channels(c)
         {
-        value.f = readbuf[3 * (j * img->width + i) + c];
+        value.f = readbuf[3 * ((img->height - 1 - j) * img->width + i) + c];
         if(swap_byte_order) value.i = GUINT32_SWAP_LE_BE(value.i);
         pix[c] = value.f;
         }
@@ -114,25 +114,13 @@ DT_OMP_FOR(collapse(2))
     for(size_t j = 0; j < img->height; j++)
       for(size_t i = 0; i < img->width; i++)
       {
-        value.f = readbuf[(j * img->width + i)];
+        value.f = readbuf[((img->height - 1 - j) * img->width + i)];
         if(swap_byte_order) value.i = GUINT32_SWAP_LE_BE(value.i);
         buf[4 * (img->width * j + i) + 2] = buf[4 * (img->width * j + i) + 1]
             = buf[4 * (img->width * j + i) + 0] = value.f;
       }
   }
 
-  float *line = (float *)calloc(4 * img->width, sizeof(float));
-  if(line == NULL) goto error_cache_full;
-
-  for(size_t j = 0; j < img->height / 2; j++)
-  {
-    memcpy(line, buf + img->width * j * 4, sizeof(float) * 4 * img->width);
-    memcpy(buf + img->width * j * 4, buf + img->width * (img->height - 1 - j) * 4,
-           sizeof(float) * 4 * img->width);
-    memcpy(buf + img->width * (img->height - 1 - j) * 4, line, sizeof(float) * 4 * img->width);
-  }
-
-  free(line);
   fclose(f);
   dt_free_align(readbuf);