Re: Efficient Sequential Access to Arrays

[robin.vowels@gmail.com]

On Monday, 16 July 2012 04:40:08 UTC+10, Keean Schupke  wrote:

> However in order to achieve this performance I needed to rework the arrays as the use of Indexes was too slow. An example of this is lets say we are accessing element 5 from array A "A(5)" this requires a multiplication to access (base_address + index * record_size). To access the neighbour A(6) also requires a multiplication. Accessing the array sequentially requires a multiplication per step.

Have you tried turning on high optimisation?

If you are accessing elements sequentially,
the optimiser will probably not do multiplications,
but instead access successive elements by means of additions.

Other factors may be relevant:
1. For example, if the size of a
   record is small-ish, the compiler may use shifts and/or
   adds/subtracts instead of multiplications.

2. The hardware multiplier may be one of the fast kind,
   in which case the time is negligible.