Re: Making literal "20" symbolic

Andy Parkins [off-list ref] writes:

I notice that there are a lot of uses of the literal 20 throughout git; I'd 
like to change them (as appropriate) to HASH_WIDTH, or similar; and maybe 
HASH_WIDTH_ASCII for the 40s.

Is there a particular header file that is appropriate to put 

#define HASH_WIDTH 20
#define HASH_WIDTH_ASCII (HASH_WIDTH*2)

Of course, I plan to review each instance to make sure I'm not changing a 
non-hash width 20.

Probably in cache.h, close to where it defines is_null_sha1(),
hashcmp(), and friends, is the right place.

There are few places that say 42 (because we have 40-hex at the
beginning of line, followed by a single whitespace and then
something should follow so line length must be at least 42
chars), so hunting them all would be a lot of work, but I do
think this is a worthwhile cleanup.