[FFmpeg-devel] [PATCH] png parser

[Peter Holik]

Michael Niedermayer schrieb:
> On Mon, Jul 06, 2009 at 09:17:23AM +0200, Peter Holik wrote:
>> Michael Niedermayer schrieb:
>> > On Wed, Jul 01, 2009 at 05:04:51PM +0200, Peter Holik wrote:
>> >> Michael Niedermayer schrieb:
>> >> > On Tue, Jun 30, 2009 at 08:47:48AM +0200, Peter Holik wrote:
>> >> >> Michael Niedermayer schrieb:
>> >> >> > On Thu, Jun 25, 2009 at 07:55:08PM +0200, Peter Holik wrote:
>> >> >> >> Michael Niedermayer schrieb:
>> >> >> >> > On Thu, Jun 25, 2009 at 02:14:14PM +0200, Peter Holik wrote:
>> >> >> > [...]
>> >> >> >
>> >> >> >
>> >> >> >> +    for (;ppc->pc.frame_start_found && i < buf_size; i++) {
>> >> >> >> +        ppc->state = (ppc->state<<8) | buf[i];
>> >> >> >
>> >> >> > why is this not using the state variable from ParseContext ?
>> >> >>
>> >> >> ok, now ParseContext state is used
>> >> >
>> >> > [...]
>> >> >
>> >> >> +typedef struct PNGParseContext
>> >> >> +{
>> >> >> +    ParseContext pc;
>> >> >> +    uint32_t index;
>> >> >
>> >> >> +    uint32_t chunk_length;
>> >> >
>> >> > unneeded, it can be read out of state64, it not needed to be stored in the
>> >> > context
>> >>
>> >> you really mean i should misuse an existing field?
>> >>
>> >> last time you told me NOT to do such things.
>> >
>> > no
>> >
>> > you already read it out of state(64) and thats what state64 is there
>> > for, of course you must not store it in state* as a 32bit value rather
>> > it naturally is in there because state64 represents the last 8 bytes
>>
>> I read out of state64 for the signature but not for png chunks.
>> Inside the for loop is not update of state64.
>> Well i could misuse state64 for chunk_length but for sourcecode readability
>> i prefer to use ppc->chunk_length.
>
> Iam quite unhappy about that as it is worse readabilitywise IMHO and requires
> chunk_length to be part of the context vs. a local variable but if its
> important to you ...

chunk_length has to be part of the context because if buffer ends with
the chunk length it can not be a local var.

>> +    for (;ppc->pc.frame_start_found && i < buf_size; i++) {
>> +        ppc->pc.state = (ppc->pc.state<<8) | buf[i];
>
>> +        if (ppc->index == 3)
>> +            ppc->chunk_length = AV_RL32(&ppc->pc.state) + 4;
>> +        else if (ppc->index == 7) {
>
> if(){
> }else

ok done, but i don't know why needed.

>> +            if (AV_RB32(&ppc->pc.state) == MKTAG('I', 'E', 'N', 'D')) {
>> +                if (ppc->chunk_length >= buf_size - i) {
>
>> +                    ppc->remaining_size = ppc->chunk_length - buf_size + i + 1;
>
> this can still overflow

how to prevent a overflow?

i think it can only overflow if ppc->chunk_length is MAXUINT and i == buf_size

>> +                    ppc->index = -1;
>> +                } else
>> +                    next = i + ppc->chunk_length + 1;
>> +                break;
>> +            } else {
>> +                ppc->index = 0;
>> +                if (ppc->chunk_length >= buf_size - i) {
>> +                    ppc->remaining_size = ppc->chunk_length - buf_size + i + 1;
>> +                    break;
>> +                } else
>> +                    i += ppc->chunk_length;
>> +                continue;
>> +            }
>
> looks like some code can be factored out

done

cu Peter
-------------- next part --------------
A non-text attachment was scrubbed...
Name: png-parser.diff
Type: text/x-diff
Size: 5053 bytes
Desc: not available
URL: <http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/attachments/20090713/ffcb3e18/attachment.diff>