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Re: [dm-devel] [PATCH v8 01/16] hashtable: introduce a small and naive hashtable



Tejun Heo wrote:
>> +#define hash_min(val, bits)						\
>> +({									\
>> +	sizeof(val) <= 4 ?						\
>> +	hash_32(val, bits) :						\
>> +	hash_long(val, bits);						\
>> +})

> Also, you probably want () around at least @val.  In general,
> it's a good idea to add () around any macro argument to avoid nasty
> surprises.

Er... not in this case, you don't.  If a macro argument is passed verbatim
as an argument to a function, it doesn't need additional parens.

That's because the one guarantee you have about a macro argument is
that it can't contain any (unquoted) commas, and there's nothing lower
precedence than the comma.  So it's safe to delimit a macro argument
with *either* parens *or* a comma.

So you can go ahead and write:

#define hash_min(val, bits) \
	(sizeof(val) <= 4 ? hash_32(val, bits) : hash_long(val, bits))

... which is easier to read, anyway.


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