Ed Hartnett wrote:
> "Greg Sjaardema" <gdsjaar@xxxxxxxxxx> writes:
>
>> I have a monstrous file with several thousand dimensions and variables
>> which is running slower than it should. I investigated the runtime
>> and found that strlen was the major time user in the NC_finddim and
>> NC_findvar calls. The obvious optimization was to cache the length of
>> the name instead of calling strlen each time. However, when I went to
>> do this, I discovered that the length is already cached as the nchars
>> field in the NC_string struct.
>>
>> I did some checks in the code and also added some assertions to the
>> code and verified that, as far as I can tell, nchars is the correct
>> length of the string. Is there a reason that it isn't used and
>> strlen() is called instead? Switching the code to use nchars dropped
>> my execution time from 20 units to 6 units. I would like to make the
>> switch, but wondered if there was some strange corner case where the
>> nchars value is incorrect and will cause problems.
>>
>> Thanks,
>> --Greg
>>
>
> Howdy Greg!
>
> Sounds interesting!
>
> Can you send your patch to support-netcdf@xxxxxxxxxxxxxxxx and we can
> take a look?
>
> Thanks,
>
> Ed
>
Actually, I didn't look close enough. The NC_string nchars actually
isn't always the length of the string. I have an alternative way to do
this which I will send tomorrow, but I'm not sure it will be worth it
for "normal-sized" files.
--Greg
