png_do_unpack(png_row_infop row_info, png_bytep row)
{
   png_debug(1, "in png_do_unpack");

#ifdef PNG_USELESS_TESTS_SUPPORTED
   if (row != NULL && row_info != NULL && row_info->bit_depth < 8)
#else
   if (row_info->bit_depth < 8)
#endif
   {
      png_uint_32 i;
      png_uint_32 row_width=row_info->width;

      switch (row_info->bit_depth)
      {
         case 1:
         {
            png_bytep sp = row + (png_size_t)((row_width - 1) >> 3);
            png_bytep dp = row + (png_size_t)row_width - 1;
            png_uint_32 shift = 7 - (int)((row_width + 7) & 0x07);
            for (i = 0; i < row_width; i++)
            {
               *dp = (png_byte)((*sp >> shift) & 0x01);
               if (shift == 7)
               {
                  shift = 0;
                  sp--;
               }
               else
                  shift++;

               dp--;
            }
            break;
         }

         case 2:
         {

            png_bytep sp = row + (png_size_t)((row_width - 1) >> 2);
            png_bytep dp = row + (png_size_t)row_width - 1;
            png_uint_32 shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
            for (i = 0; i < row_width; i++)
            {
               *dp = (png_byte)((*sp >> shift) & 0x03);
               if (shift == 6)
               {
                  shift = 0;
                  sp--;
               }
               else
                  shift += 2;

               dp--;
            }
            break;
         }

         case 4:
         {
            png_bytep sp = row + (png_size_t)((row_width - 1) >> 1);
            png_bytep dp = row + (png_size_t)row_width - 1;
            png_uint_32 shift = (int)((1 - ((row_width + 1) & 0x01)) << 2);
            for (i = 0; i < row_width; i++)
            {
               *dp = (png_byte)((*sp >> shift) & 0x0f);
               if (shift == 4)
               {
                  shift = 0;
                  sp--;
               }
               else
                  shift = 4;

               dp--;
            }
            break;
         }
      }
      row_info->bit_depth = 8;
      row_info->pixel_depth = (png_byte)(8 * row_info->channels);
      row_info->rowbytes = row_width * row_info->channels;
   }
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.