[J3] [EXTERNAL] [BULK] SCALE(x,i) with complex x

[Clune, Thomas L. (GSFC-6101)]

Hi Steve,

Extending to complex would not seem to pose any challenge.    As to why (well before my time), my guess would be that someone was attempting to emulate a specific bit of functionality in another layer (IEEE?) that did not address the complex case.

Of course back in the day, SCALE() could provide some significant performance advantage via bit-twiddling vs full multiply.     These days, though, unless an arg and result are known to be very small and cache resident, the memory access will dominate.   Given that I think a variant of your 3rd version is actually preferable in most implementations:

PROGRAM FOO
   COMPLEX A, B
   A = (1,1)
   B = (2**2) * A   ! parens added for clarity for reader
   PRINT *, B
END PROGRAM FOO

I find this implementation much more obvious than SCALE() as one needs to 1st remember which argument is which.   Of course, if I used SCALE() frequently, I might feel differently.

Not opposed to the extension – just explaining why I there may be mixed views on priority.

Cheers,


  *   Tom

From: J3 <j3-bounces at mailman.j3-fortran.org> on behalf of j3 <j3 at mailman.j3-fortran.org>
Reply-To: "kargl at uw.edu" <kargl at uw.edu>, j3 <j3 at mailman.j3-fortran.org>
Date: Saturday, November 4, 2023 at 11:29 PM
To: j3 <j3 at mailman.j3-fortran.org>
Cc: "Steven G. Kargl" <kargl at uw.edu>
Subject: [EXTERNAL] [BULK] [J3] SCALE(x,i) with complex x

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