[fpc-devel] Array indexing vs. pointers

[Jim Leonard]

(Sorry if this isn't technical enough for the developer list, but it 
requires understanding of the underlying architecture so I thought it 
was appropriate.)  I'm implementing something in FPC that will perform 
very many comparisons across sets of data, and would like to know 
whether or not FPC is more efficient with array indexing calculations 
vs. doing the pointer math myself.  For example, I have a choice of 
doing either this:

   for b:=0 to num-1 do
     diff:=src^[b]-dst^[b];

...or this:

   for b:=0 to num-1 do begin
     diff:=src^-dst^;
     inc(src);
     inc(dst);
   end;

I read a few posts from 2010 and a post from 2013 that implies FPC's 
array index calcs are just a MUL and suboptimial; is this still the 
case?  Which method produces faster code?  A third way would be to copy 
data into a dynamic array and no pointer use at all, ie. 
"diff:=src[b]-dst[b];"... is this the fastest option?

(Eventually I will be writing performance-critical sections in 
assembler, but would like to avoid doing that during early phases of my 
project.)
-- 
Jim Leonard (trixter at oldskool.org)
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