[ovs-dev] [PATCH 04/12] hash: Skip invoking mhash_add__() with zero input.

[Bodireddy, Bhanuprakash]

>-----Original Message-----
>From: Jarno Rajahalme [mailto:jarno at ovn.org]
>Sent: Friday, October 7, 2016 10:09 PM
>To: Bodireddy, Bhanuprakash <bhanuprakash.bodireddy at intel.com>
>Cc: dev at openvswitch.org
>Subject: Re: [ovs-dev] [PATCH 04/12] hash: Skip invoking mhash_add__() with
>zero input.
>
>
>> On Oct 7, 2016, at 9:17 AM, Bhanuprakash Bodireddy
><bhanuprakash.bodireddy at intel.com> wrote:
>>
>> mhash_add__() is expensive and should be only called with valid input.
>> This patch will validate the input before invoking the mhash_add__ and
>> there by saving some cpu cycles.
>>
>> Signed-off-by: Bhanuprakash Bodireddy
>> <bhanuprakash.bodireddy at intel.com>
>> Signed-off-by: Antonio Fischetti <antonio.fischetti at intel.com>
>> ---
>> lib/hash.h | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/lib/hash.h b/lib/hash.h
>> index 114a419..9bfebdb 100644
>> --- a/lib/hash.h
>> +++ b/lib/hash.h
>> @@ -70,7 +70,7 @@ static inline uint32_t mhash_add__(uint32_t hash,
>> uint32_t data)
>>
>> static inline uint32_t mhash_add(uint32_t hash, uint32_t data) {
>> -    hash = mhash_add__(hash, data);
>> +    hash = data ? mhash_add__(hash, data): hash;
>
>IMO the zero check is best placed in the function mhash_add__(), where it is
>also more evident that zero-valued data would not change the hash anyway.
>Maybe a comment to that effect would be also nice?
Agree, will do this in v2. 

Bhanu Prakash. 

>
>>     hash = hash_rot(hash, 13);
>>     return hash * 5 + 0xe6546b64;
>> }
>> --
>> 2.4.11
>>
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