Imageio PFM fixes

1. Allocate temp buffer only for what we need
2. Check for correct size of read data from file and possibly report as corrupted
3. some constify and simplifications

Author: jenshannoschwalm

src/imageio/imageio_pfm.c

@@ -41,7 +41,6 @@ dt_imageio_retval_t dt_imageio_open_pfm(dt_image_t *img,
 
   int ret = 0;
   int channels = 3;
-  float scale_factor;
   char head[2] = { 'X', 'X' };
 
   ret = fscanf(f, "%c%c\n", head, head + 1);
@@ -56,7 +55,6 @@ dt_imageio_retval_t dt_imageio_open_pfm(dt_image_t *img,
   else
     goto error_corrupt;
 
-  int read_byte;
   gboolean made_by_photoshop = TRUE;
   // We expect metadata with a newline character at the end.
   // If there is no whitespace in the first line, then this file
@@ -65,7 +63,7 @@ dt_imageio_retval_t dt_imageio_open_pfm(dt_image_t *img,
   // to the file in a different order.
   for(;;)
   {
-    read_byte = fgetc(f);
+    int read_byte = fgetc(f);
     if((read_byte == '\n') || (read_byte == EOF))
       break;
     if(read_byte < '0')          // easy way to match all whitespaces
@@ -87,22 +85,18 @@ dt_imageio_retval_t dt_imageio_open_pfm(dt_image_t *img,
   if(ret != 3)
     goto error_corrupt;
 
-  errno = 0;
   img->width = strtol(width_string, NULL, 0);
   img->height = strtol(height_string, NULL, 0);
-  scale_factor = g_ascii_strtod(scale_factor_string, NULL);
+  const float scale_factor = g_ascii_strtod(scale_factor_string, NULL);
 
-  if(errno != 0)
-    goto error_corrupt;
   if(img->width <= 0 || img->height <= 0 )
     goto error_corrupt;
 
   ret = fread(&ret, sizeof(char), 1, f);
   if(ret != 1)
     goto error_corrupt;
-  ret = 0;
 
-  int swap_byte_order = (scale_factor >= 0.0) ^ (G_BYTE_ORDER == G_BIG_ENDIAN);
+  const int swap_byte_order = (scale_factor >= 0.0) ^ (G_BYTE_ORDER == G_BIG_ENDIAN);
 
   img->buf_dsc.channels = 4;
   img->buf_dsc.datatype = TYPE_FLOAT;
@@ -112,10 +106,15 @@ dt_imageio_retval_t dt_imageio_open_pfm(dt_image_t *img,
 
   const size_t npixels = (size_t)img->width * img->height;
 
-  float *readbuf = dt_alloc_align_float(npixels * 4);
+  float *readbuf = dt_alloc_align_float(npixels * channels);
   if(!readbuf)
     goto error_cache_full;
-
+  ret = fread(readbuf, sizeof(float) * channels, npixels, f);
+  if(ret != npixels)
+  {
+    dt_free_align(readbuf);
+    goto error_corrupt;
+  }
   // We use this union to swap the byte order in the float value if needed
   union { float as_float; guint32 as_int; } value;
 
@@ -124,45 +123,37 @@ dt_imageio_retval_t dt_imageio_open_pfm(dt_image_t *img,
   // the rows in the process of filling the output buffer with data
   if(channels == 3)
   {
-    ret = fread(readbuf, 3 * sizeof(float), npixels, f);
-    size_t target_row = 0;
-
-DT_OMP_FOR(collapse(2))
+    DT_OMP_FOR(collapse(2))
     for(size_t row = 0; row < img->height; row++)
+    {
+      const size_t target_row = made_by_photoshop ? row : img->height - 1 - row;
       for(size_t column = 0; column < img->width; column++)
       {
         dt_aligned_pixel_t pix = {0.0f, 0.0f, 0.0f, 0.0f};
-        if(made_by_photoshop)
-          target_row = row;
-        else
-          target_row = img->height - 1 - row;
         for_three_channels(c)
         {
-        value.as_float = readbuf[3 * (target_row * img->width + column) + c];
-        if(swap_byte_order) value.as_int = GUINT32_SWAP_LE_BE(value.as_int);
-        pix[c] = value.as_float;
+          value.as_float = readbuf[3 * (target_row * img->width + column) + c];
+          if(swap_byte_order) value.as_int = GUINT32_SWAP_LE_BE(value.as_int);
+          pix[c] = value.as_float;
         }
         copy_pixel_nontemporal(&buf[4 * (img->width * row + column)], pix);
       }
+    }
   }
   else
   {
-    ret = fread(readbuf, sizeof(float), npixels, f);
-    size_t target_row = 0;
-
-DT_OMP_FOR(collapse(2))
+    DT_OMP_FOR(collapse(2))
     for(size_t row = 0; row < img->height; row++)
+    {
+      const size_t target_row = made_by_photoshop ? row : img->height - 1 - row;
       for(size_t column = 0; column < img->width; column++)
       {
-        if(made_by_photoshop)
-          target_row = row;
-        else
-          target_row = img->height - 1 - row;
         value.as_float = readbuf[target_row * img->width + column];
         if(swap_byte_order) value.as_int = GUINT32_SWAP_LE_BE(value.as_int);
         buf[4 * (img->width * row + column) + 2] = buf[4 * (img->width * row + column) + 1]
             = buf[4 * (img->width * row + column) + 0] = value.as_float;
       }
+    }
   }
 
   fclose(f);