Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!srhqla!demott!kdq
From: kdq@demott.COM (Kevin D. Quitt)
Newsgroups: comp.lang.c
Subject: Re: Just a minor new twist on free()
Message-ID: <687@demott.COM>
Date: 6 Oct 90 17:03:52 GMT
References: <1990Oct04.110928.16788@virtech.uucp>
Reply-To: kdq@demott.COM (Kevin D. Quitt)
Organization: DeMott Electronics Co., Van Nuys CA
Lines: 44

In article <1990Oct04.110928.16788@virtech.uucp> cpcahil@virtech.uucp (Conor P. Cahill) writes:
>It appears you took my comments as a personal attack, which they were not
>meant to be.  However, you raised some points that I will respond to...
>
>In article <PDS.90Oct3103126@lemming.webo.dg.com> pds@lemming.webo.dg.com (Paul D. Smith) writes:
>>While your simple case might indeed not be much of a performance hit,
>>what about something like:
>>
>>    #define ARRAY_LEN   10000
>>    char *array[ARRAY_LEN], *ap;
>>    int i;
>>
>>    for (ap = array, i = 0; i < ARRAY_LEN; ++i, ++ap)
>>    {
>>        if (ap != NULL)
>>            free(ap)
>>    }
>>
>>Now, *this* is a significant performance hit, if you consider an extra
>
>No it is not.  Actually, if array has greater than a small percentage 
>of NULL pointers, the savings of the function call by the if test will
>be substantial.   Rember, comparisons (especially comparisons against 
>zero) are a very cheap operation.  Function calls are not.
>
>>10000 comparisons.  Before you retort about using memset() or bzero(),
>>please read the FAQ on NULL pointers ... and no, I wouldn't do it this

    On the three systems I'm using, this is faster than the call without
the if, not slower! Testing for 0 is *much* faster than the overhead of
a function call - which function starts with a test for zero.  So if I
test first, I pay the penalty for comparing against zero.  If it's zero
I have a major win; if it's not, I pay a few percent in performance
penalty.  Have you folks actually tried timing your examples instead
of just using gedanken experiments?


-- 
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Kevin D. Quitt         demott!kdq   kdq@demott.com
DeMott Electronics Co. 14707 Keswick St.   Van Nuys, CA 91405-1266
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