On Fri, 26 Jun 1998, Glynn Clements wrote:
>> The result for x+1 is calculated in register, which is then saved
>> into *stack* before calling the function again (or maybe just variable
>> x is saved into stack, but something in any case is saved into stack).
>
>Again, this is an implementation issue. On RISC architectures (which
To be more precise is _only_ a GCC issue. GCC i386 doesn' t use registers
for passing argument to functions only for historical reasons and because
other i386 compilers uses stack (so if GCC would do different things
object and libs couldn' t be sharded between compilers). For example
syscalls on i386 use registers to pass parameters to the kernel and I can'
t see no differences between `int 0x80' and `call' asm inst...
>> The thing about what you were talking was not *stackless* recursion,
>> but in fact, *parameterless* recursion. The parameters are passed
>> in GCC using stack, which is avoided this way but they could be passed
>> in registers *or* as global variables too. But stack is needed anyway.
>
>No, not always. The point of this paper was that if the transformation
>which is applied to the parameters can be inverted (and in many cases
>it can), you don't need to use a stack.
>
>Clearly, this can't always be done (e.g. searching a tree which
>doesn't have `up' pointers), but in many cases it can.
And infact the great avantage of recursion is when we can' t avoid the use
of the stack. For compute a factorial the complexity is so low that there'
s no need to use recursion... I think that the great thing of the
recursion is the stack ;-).
Andrea[s] Arcangeli
