Re: timings. sub proc returns varying string.

[Hans Boldt <boldt@xxxxxxxxxx>]

Steve Richter wrote:
> two procedures.  both return a varying length string.  Just the max size
> differs. 10a vs 32000a.
>
> pTestFunc1        b
> dTestFunc1        pi         32000a   varying
> c                   return    'abc'
> p                 e
>
> pTestFunc2        b
> dTestFunc2        pi            10a   varying
> c                   return    'abc'
> p                 e
>
> When I run them side by side in a timing loop, the 10a return value
> functions runs much quicker than the 32000a version.
> d ch80            s             80a   varying
> c                   eval      ch80 = TestFunc1
> c                   eval      ch80 = TestFunc2
>
> 30,000 times.  66 msec vs 2554 msec.
>
> I was hoping the run times would be comparable.
>
> When I assign a literal value to a varying char variable, the run times are
> the same, regardless of the size of the string.
>
> Any explanation why the run time difference?
The bottleneck is the RETURN statement. Unfortunately, W-Code
doesn't recognize varying length character as a distinct data type,
since W-Code represents a fairly low-level machine model. As a
result, your procedure PTESTFUNC1 always returns 32002 bytes and
your procedure PTESTFUNC2 always returns 12 bytes, regardless of the
actual meaningful length of the return value. In all other places in
the language, we can deal with just the exact number of bytes we
need to, but RETURN has to copy all of the bytes of the variable.

Bummer, eh? The lesson is to declare your string procedures with
more modest return value lengths.

Cheers!  Hans