GP32 Malloc

[pea]

Hi all,

I am re-writing the GIF routines because the malloc/free flow is much less than optimal (i.e. its pretty damn random, malloc in one function, free in a completely different one).

Just wanted to confirm. If I have a struct like this:

typedef struct tGPD_gif{
	int width;	
	int height;
	short *imag;
}tGPD_gif;

And then I allocate memory for the struct like this:

tGPD_gif *gif;
gif = malloc( some_size );
gif->imag = malloc( some_other_size);

Then freeing 'gif' without first freeing 'gif->imag' is going to result in a leak, right?

Cheers,
Pea

 

[Squidge]

Correct. Also, if you free "gif" first, then try to delete "gif->image", you may be dereferencing an invalid pointer, so could even crash the machine and require a reset.

Then freeing 'gif' without first freeing 'gif->imag' is going to result in a leak, right?

​

 

[kmkzk]

Hi!
You have to free the image data first an then free the gif struct. For allocating the gif struct use malloc(sizeof(tGPD_gif)) and for allocating the gif, something like malloc(heigth*width*sizeof(short)).
Correct me if i'm wrong.

When i use malloc, my programs crash on the gp. It gets ok when using gp_mem_func.malloc(...)

 

[don]

When i use malloc, my programs crash on the gp. It gets ok when using gp_mem_func.malloc(...)

​

When using the original Gamepark SDK, _ALWAYS_ use gp_mem functions, instead of libc mem functions! When using Mirko's SDK, you can use libc mem functions.

 

[pea]

Thanks for the last tip kmkzk and don. I was going to ask that question next because I see the original GIF lib uses something like gm_malloc... mine has been working ok on geepee32 so far (I don't have a GP32 yet)

 

[pea]

Just another Q regarding malloc and free..

If I call 'free' on a struct that HASN'T yet had memory allocated using malloc, will my app crash? In other words...

Can I do this (extrremely simplified example):

typedef struct tMyStruct{
  int number;
}

void main( void ){
  tMyStruct *t1;
  tMyStruct *t2;

  t1 = createMyStruct( -3 ); // will return NULL
  t2 = createMyStruct( 5 ); // will return valid struct

  free( t1 ); // #### THIS #### <- t1 doesnt actually have memory allocated
  free( t2 );
}

tMyStruct* createMyStruct( num ){
  tMyStruct *mine;
  
  if (num<0){
    return NULL;
  }
  mine = (tMyStruct*)malloc( sizeof(tMyStruct) );
  mine->number = num;
  
  return mine;
}

Or do I have to do this?

typedef struct tMyStruct{
  int number;
}

void main( void ){
  tMyStruct *t1;
  tMyStruct *t2;

  t1 = createMyStruct( -3 ); // will return NULL
  t2 = createMyStruct( 5 ); // will return valid struct

  if (t1!=NULL){ free( t1 ); }
  if (t2!=NULL){ free( t2 ); }
}

tMyStruct* createMyStruct( num ){
  tMyStruct *mine;
  
  mine=NULL;

  if (num>=0){
    mine = (tMyStruct*)malloc( sizeof(tMyStruct) );
    mine->number = num;
  }
  
  return mine;
}

I don't want to have to check for NULLs if I don't specifically need to.

Also, are pointers NULL by default, or could they be pointing to arbitrary memory locations and need to be manually assigned NULL?

 

[Palmic]

Just another Q regarding malloc and free..

If I call 'free' on a struct that HASN'T yet had memory allocated using malloc, will my app crash? In other words...

Can I do this (extrremely simplified example):

typedef struct tMyStruct{
  int number;
}

void main( void ){
  tMyStruct *t1;
  tMyStruct *t2;

  t1 = createMyStruct( -3 ); // will return NULL
  t2 = createMyStruct( 5 ); // will return valid struct

  free( t1 ); // #### THIS #### <- t1 doesnt actually have memory allocated
  free( t2 );
}

tMyStruct* createMyStruct( num ){
  tMyStruct *mine;
  
  if (num<0){
    return NULL;
  }
  mine = (tMyStruct*)malloc( sizeof(tMyStruct) );
  mine->number = num;
  
  return mine;
}

Or do I have to do this?

typedef struct tMyStruct{
  int number;
}

void main( void ){
  tMyStruct *t1;
  tMyStruct *t2;

  t1 = createMyStruct( -3 ); // will return NULL
  t2 = createMyStruct( 5 ); // will return valid struct

  if (t1!=NULL){ free( t1 ); }
  if (t2!=NULL){ free( t2 ); }
}

tMyStruct* createMyStruct( num ){
  tMyStruct *mine;
  
  mine=NULL;

  if (num>=0){
    mine = (tMyStruct*)malloc( sizeof(tMyStruct) );
    mine->number = num;
  }
  
  return mine;
}

I don't want to have to check for NULLs if I don't specifically need to.

Also, are pointers NULL by default, or could they be pointing to arbitrary memory locations and need to be manually assigned NULL?

​

Hi Pea,

Under my Linux OS, I've just checked the manual page for free (by typing "man 3 free"), and here is what it tells :

"free(void* ptr) frees the memory space pointed to by ptr, which must have been returned by a previous call to malloc(), calloc(), or realloc(). Otherwise, or if free(ptr) has already been called before, undefined behavior occurs. If ptr is NULL, no operation is performed".

So I think you should check for NULL, and just after a free (ptr), do a ptr=NULL .

Could you please post here, or on your web site, your complete modified source for GIF loading, because I'm a bit lazy to adapt it for Mirko SDK...

Thanks...

 

[pea]

Hi Palmic,

Thanks for your reply. Just after posting I spent a while debugging a problem, and it turned out to be exactly the issue here - I was trying to free a struct that had already been freed, and it kept crashing. I don't have any sort of debugger, so it is very slow - I comment out all the code, and then uncomment sections at a time until geepee32 crashes, and then I narrow down the prob!!

There is a bug in the code whereby the resulting colours are completely screwed up unless the palette has all 256 colours! For example, a GIF with only 12 colours will have random colours. I am trying to work on this, but does anyone have any idea as to why?

I will post my GIF code on my website. Please note that is loads the GIF into a custom struct, which is of the form:

typedef struct tGPD_canvas{
	int width;
	int height;
	unsigned short *data;
}tGPD_canvas;

There are two functions you can use to load the GIFs (I have used the 16bpp version, not rov's modified 8bpp version). One loads a GIF from SMC, and the other simply decodes a GIF already in memory.

You can also specify whether you want the code to rotate the GIF data by 90degrees. This could be the default, but I wanted to account for GIFs that are already pre-rotated.

// ### canvasCreateFromGif
// Assigns memory and loads a GIF from the smc. The GIF is converted
// to a 16bpp canvas structure.
extern tGPD_canvas* gpd_canvasCreateFromGif(
	char *filename,      // in:  path to GIF file on smc
	char rotate90,      // in:  If non zero will rotate data 90 deg (not req. for pre-rotated images)
	int *outError      	// out:  Error code (see defines above)
);

// ### canvasCreateFromGifBuf
// Assigns memory and decodes a GIF file stored in memory (buffer). The
// GIF is converted to a 16bpp canvas structure.
extern tGPD_canvas* gpd_canvasCreateFromGifBuf(
	unsigned char *gifdata,  // in:  pointer to the GIF data in memory
	char rotate90,      // in:  If non zero will rotate data 90 deg (not req. for pre-rotated images)
	int *outError      	// out:  Error code (see defines above)
);

The functions are used like this:

tGPD_canvas *canvas;
int res;

canvas = gpd_canvasCreateFromGif( "dev0:\\gpmm\\mygif.gif", 1, &res );
if (res){
  // error occured
}else{
  ...
  gpd_canvasFree( canvas );
}

EDIT:
Code can be found here:
http://www.pea.co.nz/gp32/gpd_downloads.php