Re: Ada vs C implementation efficiency

[eachus@largo.mitre.org (Robert I. Eachus)]

     There are "benchmarks" which will (almost) always run faster in
Ada than in C, and vice-versa.  In general however, for good compilers
and good benchmarks a program will run fastest in the language it was
originally written in.  Thus, the Dhrystone benchmark, originally in
Ada, normally runs faster in Ada than in C, and people complain that
it overuses the string operations in C.

     If take an application and write it (from scratch) in several
languages with each version written by a team experienced in that
language, it usually turns out that you measure the difference in
cultures not the difference in compilers. 

     I once had the opportunity to do this with a package heavy on
matrix operations in FORTRAN, Pascal, and Ada.  The FORTRAN version
was fastest, the Pascal version had the lowest error bounds on
non-stiff matrices, and the Ada version was the only one that could be
trusted with near singular data.  Which one is "best"?

     We did a "second iteration," putting checking code into the
FORTRAN and Pascal versions, and using the Pascal code in all three
versions (after conditioning), and now the program performance
differences were in the noise.  (The Ada I/O was slower, and the
FORTRAN floating point with overflow checking was much more
cumbersome, etc. so there were input cases where each version was
"fastest," but now all were correct...)

     My personal approach, based on this experiment and others, is to
go for correctness first, and if you need better performance, look at
the algorithms, THEN at the code.  I have gotten to the point of
looking at generated code once or twice, but in every case I have
found a way to coerce the compiler to generate what I wanted.

--

					Robert I. Eachus

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