Release Notes

Open Source Used In AsyncOS 8.8 for Cisco Web Security Appliances

* If you don't need the JPEG object any more, just call

jpeg_destroy_compress() or jpeg_destroy() to release memory. This is

legitimate at any point after calling jpeg_create_compress() --- in fact,

it's safe even if jpeg_create_compress() fails.

* If you want to re-use the JPEG object, call jpeg_abort_compress(), or call

jpeg_abort() which works on both compression and decompression objects.

This will return the object to an idle state, releasing any working memory.

jpeg_abort() is allowed at any time after successful object creation.

Note that cleaning up the data destination, if required, is your

responsibility; neither of these routines will call term_destination().

(See "Compressed data handling", below, for more about that.)

jpeg_destroy() and jpeg_abort() are the only safe calls to make on a JPEG

object that has reported an error by calling error_exit (see "Error handling"

for more info). The internal state of such an object is likely to be out of

whack. Either of these two routines will return the object to a known state.

Decompression details

---------------------

Here we revisit the JPEG decompression outline given in the overview.

1. Allocate and initialize a JPEG decompression object.

This is just like initialization for compression, as discussed above,

except that the object is a "struct jpeg_decompress_struct" and you

call jpeg_create_decompress(). Error handling is exactly the same.

Typical code:

struct jpeg_decompress_struct cinfo;

struct jpeg_error_mgr jerr;

...

cinfo.err = jpeg_std_error(&jerr);

jpeg_create_decompress(&cinfo);

(Both here and in the IJG code, we usually use variable name "cinfo" for

both compression and decompression objects.)

2. Specify the source of the compressed data (eg, a file).

As previously mentioned, the JPEG library reads compressed data from a "data

source" module. The library includes one data source module which knows how