[FFmpeg-devel] [PATCH] png parser

[Peter Holik]

Michael Niedermayer schrieb:
> On Fri, Jul 17, 2009 at 09:40:13AM +0200, Peter Holik wrote:
>> Michael Niedermayer schrieb:
>> > On Mon, Jul 13, 2009 at 05:01:00PM +0200, Peter Holik wrote:
>> >> 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.
>> >
>> > its in state64
>>
>> no, please have a look at ff_combine_frame.
>> the only position where state64 is updated is if next is negative.
>
> grep state parser.c will show state64 is updated at every point that state is.

#> grep state64 parser.c
pc->state64 = (pc->state64<<8) | pc->buffer[pc->last_index + next];

only one time, where state64 is updated

#> grep -B30 state64 parser.c
    /* copy into buffer end return */
    if(next == END_NOT_FOUND){
        void* new_buffer = av_fast_realloc(pc->buffer, &pc->buffer_size, (*buf_size) + pc->index +
FF_INPUT_BUFFER_PADDING_SIZE);

        if(!new_buffer)
            return AVERROR(ENOMEM);
        pc->buffer = new_buffer;
        memcpy(&pc->buffer[pc->index], *buf, *buf_size);
        pc->index += *buf_size;
        return -1;
    }

    *buf_size=
    pc->overread_index= pc->index + next;

    /* append to buffer */
    if(pc->index){
        void* new_buffer = av_fast_realloc(pc->buffer, &pc->buffer_size, next + pc->index +
FF_INPUT_BUFFER_PADDING_SIZE);

        if(!new_buffer)
            return AVERROR(ENOMEM);
        pc->buffer = new_buffer;
        memcpy(&pc->buffer[pc->index], *buf, next + FF_INPUT_BUFFER_PADDING_SIZE );
        pc->index = 0;
        *buf= pc->buffer;
    }

    /* store overread bytes */
    for(;next < 0; next++){
        pc->state = (pc->state<<8) | pc->buffer[pc->last_index + next];
        pc->state64 = (pc->state64<<8) | pc->buffer[pc->last_index + next];

this is in parser.c/ff_combine_frame

if next == END_NOT_FOUND there is no update of state64

as you can see state64 is only updated id next < 0 (/* store overread bytes */)


please apply my patch

cu Peter

PS: Have you found a new ISP in Vienna?