    /* pngmem.c - stub functions for memory allocation
     *
     * Copyright (c) 2018 Cosmin Truta
     * Copyright (c) 1998-2002,2004,2006-2014,2016 Glenn Randers-Pehrson
     * Copyright (c) 1996-1997 Andreas Dilger
     * Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.
     *
     * This code is released under the libpng license.
     * For conditions of distribution and use, see the disclaimer
     * and license in png.h
     *
     * This file provides a location for all memory allocation.  Users who
     * need special memory handling are expected to supply replacement
     * functions for png_malloc() and png_free(), and to use
     * png_create_read_struct_2() and png_create_write_struct_2() to
     * identify the replacement functions.
     */

    #include "pngpriv.h"

    #if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED)
    /* Free a png_struct */
    void /* PRIVATE */
    png_destroy_png_struct(png_structrp png_ptr)
    {
       if (png_ptr != NULL)
       {
          /* png_free might call png_error and may certainly call
           * png_get_mem_ptr, so fake a temporary png_struct to support this.
           */
          png_struct dummy_struct = *png_ptr;
          memset(png_ptr, 0, (sizeof *png_ptr));
          png_free(&dummy_struct, png_ptr);

    #     ifdef PNG_SETJMP_SUPPORTED
             /* We may have a jmp_buf left to deallocate. */
             png_free_jmpbuf(&dummy_struct);
    #     endif
       }
    }

    /* Allocate memory.  For reasonable files, size should never exceed
     * 64K.  However, zlib may allocate more than 64K if you don't tell
     * it not to.  See zconf.h and png.h for more information.  zlib does
     * need to allocate exactly 64K, so whatever you call here must
     * have the ability to do that.
     */
    PNG_FUNCTION(png_voidp,PNGAPI
    png_calloc,(png_const_structrp png_ptr, png_alloc_size_t size),PNG_ALLOCATED)
    {
       png_voidp ret;

       ret = png_malloc(png_ptr, size);

       if (ret != NULL)
          memset(ret, 0, size);

       return ret;
    }

    /* png_malloc_base, an internal function added at libpng 1.6.0, does the work of
     * allocating memory, taking into account limits and PNG_USER_MEM_SUPPORTED.
     * Checking and error handling must happen outside this routine; it returns NULL
     * if the allocation cannot be done (for any reason.)
     */
    PNG_FUNCTION(png_voidp /* PRIVATE */,
    png_malloc_base,(png_const_structrp png_ptr, png_alloc_size_t size),
        PNG_ALLOCATED)
    {
       /* Moved to png_malloc_base from png_malloc_default in 1.6.0; the DOS
        * allocators have also been removed in 1.6.0, so any 16-bit system now has
        * to implement a user memory handler.  This checks to be sure it isn't
        * called with big numbers.
        */
    #ifndef PNG_USER_MEM_SUPPORTED
       PNG_UNUSED(png_ptr)
    #endif

       /* Some compilers complain that this is always true.  However, it
        * can be false when integer overflow happens.
        */
       if (size > 0 && size <= PNG_SIZE_MAX
    #     ifdef PNG_MAX_MALLOC_64K
             && size <= 65536U
    #     endif
          )
       {
    #ifdef PNG_USER_MEM_SUPPORTED
          if (png_ptr != NULL && png_ptr->malloc_fn != NULL)
             return png_ptr->malloc_fn(png_constcast(png_structrp,png_ptr), size);

          else
    #endif
             return malloc((size_t)size); /* checked for truncation above */
       }

       else
          return NULL;
    }

    #if defined(PNG_TEXT_SUPPORTED) || defined(PNG_sPLT_SUPPORTED) ||\
       defined(PNG_STORE_UNKNOWN_CHUNKS_SUPPORTED)
    /* This is really here only to work round a spurious warning in GCC 4.6 and 4.7
     * that arises because of the checks in png_realloc_array that are repeated in
     * png_malloc_array.
     */
    static png_voidp
    png_malloc_array_checked(png_const_structrp png_ptr, int nelements,
        size_t element_size)
    {
       png_alloc_size_t req = (png_alloc_size_t)nelements; /* known to be > 0 */

       if (req <= PNG_SIZE_MAX/element_size)
          return png_malloc_base(png_ptr, req * element_size);

       /* The failure case when the request is too large */
       return NULL;
    }

    PNG_FUNCTION(png_voidp /* PRIVATE */,
    png_malloc_array,(png_const_structrp png_ptr, int nelements,
        size_t element_size),PNG_ALLOCATED)
    {
       if (nelements <= 0 || element_size == 0)
          png_error(png_ptr, "internal error: array alloc");

       return png_malloc_array_checked(png_ptr, nelements, element_size);
    }

    PNG_FUNCTION(png_voidp /* PRIVATE */,
    png_realloc_array,(png_const_structrp png_ptr, png_const_voidp old_array,
        int old_elements, int add_elements, size_t element_size),PNG_ALLOCATED)
    {
       /* These are internal errors: */
       if (add_elements <= 0 || element_size == 0 || old_elements < 0 ||
          (old_array == NULL && old_elements > 0))
          png_error(png_ptr, "internal error: array realloc");

       /* Check for overflow on the elements count (so the caller does not have to
        * check.)
        */
       if (add_elements <= INT_MAX - old_elements)
       {
          png_voidp new_array = png_malloc_array_checked(png_ptr,
              old_elements+add_elements, element_size);

          if (new_array != NULL)
          {
             /* Because png_malloc_array worked the size calculations below cannot
              * overflow.
              */
             if (old_elements > 0)
                memcpy(new_array, old_array, element_size*(unsigned)old_elements);

             memset((char*)new_array + element_size*(unsigned)old_elements, 0,
                 element_size*(unsigned)add_elements);

             return new_array;
          }
       }

       return NULL; /* error */
    }
    #endif /* TEXT || sPLT || STORE_UNKNOWN_CHUNKS */

    /* Various functions that have different error handling are derived from this.
     * png_malloc always exists, but if PNG_USER_MEM_SUPPORTED is defined a separate
     * function png_malloc_default is also provided.
     */
    PNG_FUNCTION(png_voidp,PNGAPI
    png_malloc,(png_const_structrp png_ptr, png_alloc_size_t size),PNG_ALLOCATED)
    {
       png_voidp ret;

       if (png_ptr == NULL)
          return NULL;

       ret = png_malloc_base(png_ptr, size);

       if (ret == NULL)
           png_error(png_ptr, "Out of memory"); /* 'm' means png_malloc */

       return ret;
    }

    #ifdef PNG_USER_MEM_SUPPORTED
    PNG_FUNCTION(png_voidp,PNGAPI
    png_malloc_default,(png_const_structrp png_ptr, png_alloc_size_t size),
        PNG_ALLOCATED PNG_DEPRECATED)
    {
       png_voidp ret;

       if (png_ptr == NULL)
          return NULL;

       /* Passing 'NULL' here bypasses the application provided memory handler. */
       ret = png_malloc_base(NULL/*use malloc*/, size);

       if (ret == NULL)
          png_error(png_ptr, "Out of Memory"); /* 'M' means png_malloc_default */

       return ret;
    }
    #endif /* USER_MEM */

    /* This function was added at libpng version 1.2.3.  The png_malloc_warn()
     * function will issue a png_warning and return NULL instead of issuing a
     * png_error, if it fails to allocate the requested memory.
     */
    PNG_FUNCTION(png_voidp,PNGAPI
    png_malloc_warn,(png_const_structrp png_ptr, png_alloc_size_t size),
        PNG_ALLOCATED)
    {
       if (png_ptr != NULL)
       {
          png_voidp ret = png_malloc_base(png_ptr, size);

          if (ret != NULL)
             return ret;

          png_warning(png_ptr, "Out of memory");
       }

       return NULL;
    }

    /* Free a pointer allocated by png_malloc().  If ptr is NULL, return
     * without taking any action.
     */
    void PNGAPI
    png_free(png_const_structrp png_ptr, png_voidp ptr)
    {
       if (png_ptr == NULL || ptr == NULL)
          return;

    #ifdef PNG_USER_MEM_SUPPORTED
       if (png_ptr->free_fn != NULL)
          png_ptr->free_fn(png_constcast(png_structrp,png_ptr), ptr);

       else
          png_free_default(png_ptr, ptr);
    }

    PNG_FUNCTION(void,PNGAPI
    png_free_default,(png_const_structrp png_ptr, png_voidp ptr),PNG_DEPRECATED)
    {
       if (png_ptr == NULL || ptr == NULL)
          return;
    #endif /* USER_MEM */

       free(ptr);
    }

    #ifdef PNG_USER_MEM_SUPPORTED
    /* This function is called when the application wants to use another method
     * of allocating and freeing memory.
     */
    void PNGAPI
    png_set_mem_fn(png_structrp png_ptr, png_voidp mem_ptr, png_malloc_ptr
      malloc_fn, png_free_ptr free_fn)
    {
       if (png_ptr != NULL)
       {
          png_ptr->mem_ptr = mem_ptr;
          png_ptr->malloc_fn = malloc_fn;
          png_ptr->free_fn = free_fn;
       }
    }

    /* This function returns a pointer to the mem_ptr associated with the user
     * functions.  The application should free any memory associated with this
     * pointer before png_write_destroy and png_read_destroy are called.
     */
    png_voidp PNGAPI
    png_get_mem_ptr(png_const_structrp png_ptr)
    {
       if (png_ptr == NULL)
          return NULL;

       return png_ptr->mem_ptr;
    }
    #endif /* USER_MEM */
    #endif /* READ || WRITE */