[PATCH] Fix 32-bit overflow in Divesoft Freedom time handling

[Anton Lundin]

On 02 October, 2015 - Linus Torvalds wrote:

> Commit 31fb2e4c62ab ("Avoid possible sign extension") handled the
> problem when a "unsigned char" is shifted 24 bits left, and becomes a
> "signed int".  By casting the result to uint32_t, that signed case won't
> happen.
> 

The root bug was mine. Another one of C's wonderful things that i didn't
know about.

> Of course, it's not at all clear that the 32-bit number is actually
> unsigned to begin with.  Maybe it's meant to be signed, the way
> traditional 32-bit unix time_t is.  Maybe the Divesoft Freedom was
> designed to also be able to import dives from before Jan 1, 2000.  Who
> knows? Not me.  I've never seen one of those things. 
> 

Most of the work to import the Divesoft files was done by
reverse-engineering, but after a while we got a answer from the Divesoft
folks with a C header containing structs, enums and typedef's on how the
format actually looks.

The tings we never managed to figure out was corrected then. One real
gotcha was the 10-bit signed temp field in 0.1 C. I'd never managed to
guess that it was 10-bit.


Anyhow, the dive start timestamp is a 32-bit signed in seconds since
2000-01-01 00:00:00, according to the header file and the comments in
it.


//Anton


-- 
Anton Lundin	+46702-161604