[ET Trac] [Einstein Toolkit] #235: Improve performance of Fortran index calculations

[Einstein Toolkit]

#235: Improve performance of Fortran index calculations
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 Reporter:  eschnett     |       Owner:     
     Type:  enhancement  |      Status:  new
 Priority:  minor        |   Milestone:     
Component:  Cactus       |     Version:     
 Keywords:               |  
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 In Fortran, Cactus currently declares grid functions e.g. as (this is the
 expansion of DECLARE_CCTK_ARGUMENTS)

   REAL*8 gxx (X0metric,X1metric,X2metric)

 where X0metric etc. are integers passed into the routine. Each grid
 function group has its own, independent size. This has two disadvantages:

 1. The compiler does not know that all grid functions have the same size
 (namely cctk_lsh), and thus has to perform array index calculations
 separately for each group
 2. The argument list is longer than neded

 The enclosed patch declares grid functions via cctk_lsh. Grid arrays are
 still declared independently.

 This reduces the code size of e.g. GRHydro/GRHydro_Tmunu.F90 from 6836 to
 6241 bytes on my system. I have not attempted to measure a performance
 difference.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/235>
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