On 25 January 2018 at 10:18, Dave Wade <[email protected]> wrote:
> I don't know if Fortran H does loop unrolling, but some compilers that are > targeted at Vector Processors do. > FORTRAN can be a pig of a language though, especially with a poor > compiler. Even worse, on two dimensional arrays, the data is stored as > columns, not rows. > (I think that’s correct. So if you vary the last subscript, you leap all > over storage. Typically Fortran users want to write code where the last > subscript varies fastest resulting in excessive paging. > Reversing the subscript order in such programs can produce a significant > performance improvements. > Long time ago we evaluated the vector feature and got the relevant FORTRAN compiler with it. Outcome was that we passed on the vector feature, but kept the compiler as it got 90% of the improvement also on the non-vector CPU :-) In those days I could also speed up a PASCAL/VS program by a factor 5 when I added 6 unused elements to all arrays with 250 elements and defined the index as integer rather than 1..250. Rob
