DECR macro signedness

[Steve Dispensa]

Sorry if this is well known (I suspect it is, based on some of the code), but DECR_LEN and friends have an integer underflow problem if they're passed unsigned quantities. Spot-checking the code shows that it's generally called with signed quantities, but I didn't see any documentation pointing out the problem.

Here's a patch if you want it; it uses the C99 intmax_t type to make a signed copy of the potentially unsigned argument for the negativity test.

Apologies if this is old news.

 -Steve

decr_patch
Description: decr_patch