Re: [ProgSoc] Need info on registers vs stacks

[Telford Tendys <telford@nospam.progsoc.uts.edu.au>]

On Mon, Oct 09, 2000 at 06:39:52PM +1100, Colin Yip wrote:
> 
> Well, I guess the subject heading says it all, so basically I have several
> questions:
> 
> 1) How do each of them work, in layman's terms?

With a stack you can push, pop and roll. This allows you to move data
on and off the stack and also to shuffle the data that is already on the 
stack.

> 2) What advantages/disadvantages does each of the two confer when it comes
> to manipulating data, in terms of at the processor level?

Stack advantages:
-- simplicity of concept, easy to program small tasks.
-- neatly incorporates subroutine calling convention.
-- supports recursion.

Stack disadvantages:
-- when your stack pointer gets screwed, so are you (bad error recovery)
-- slow on most hardware (because most hardware is register oriented,
   also registers are easier to implement in hardwar).
-- can be difficult to remember where you put things on the stack
   (programming complex stuff can be tricky, good tools help).
-- can end up being slow if circumstance results in you needing to
   reshuffle the order of stack data often (rethinking your algorithm
   sometimes fixes this).

Register advantages:
-- can access any register at any time with equal difficulty.
-- most hardware is register oriented so registers are usually fast.
-- can easily associate data with register, so compilers and
   programmers get away with less shuffling.
-- register based hardware is easy to implement.

Register disadvantages:
-- i386 hardware has hardly any registers, and i386 hardware is everywhere.
-- all hardware has a limited number of registers.
-- if you want to support recursion you need a stack anyway.
-- calling conventions between subroutines get complicated when
   using registers (especially when you find that you need a stack
   as well as your registers).

-- 
S1G: 28656193 seconds remaining			- Tel
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