recursion in pasm (and timings)

[Aldo Calpini]

hi there,
the Examples page on www.parrotcode.org states this about subroutines:

    The first five registers (I0-I4, S0-S4, P0-P4, N0-N4) are scratch 
    and do not have to be preserved by the callee. 

this seems to be false for *recursive* subroutines. this is my PASM
code fibo.pasm (it calculates the fibonacci number of 32):

          set I0, 32
          bsr FIBO
          print I0
          print "\n"
          end
FIBO:     lt I0, 2, FIBO_ONE
          set I1, I0
          set I2, I1
          dec I2, 2
          set I0, I2
          save I1
          save I2
          save I3
          bsr FIBO
          restore I3
          restore I2
          restore I1
          set I1, I0
          inc I2
          set I0, I2
          save I1
          save I2
          save I3
          bsr FIBO
          restore I3
          restore I2
          restore I1
          add I0, I0, I1
          branch FIBO_END
FIBO_ONE: set I0, 1
FIBO_END: ret

for this code to work correctly, I need to save and restore I1, I2, I3
on each recursive call. am I missing something or is just something that
needs to be documented?

and now for timings: I tested the new parrot (checked out some minutes ago)
with JIT v2 enabled and these are the results:

                        CPU    MEM
parrot fibo.pbc        8.74    736
parrot -j fibo.pbc     6.13    772

just for reference, these are the times from other languages:

                        CPU    MEM
Visual C++ (6.0)       0.13    452
gcc (2.95.3)           0.20   1344
C# (7.00.9466)         0.24   3888
java (1.4.0-b92)       0.58   4972
python (2.1.1)        14.72   2128
perl (5.6.1)          21.89   1416
ruby (1.6.5)          29.71   1912

note that comparison with parrot is not really fair because all the other 
programs accept the number (32 in our case) from the command line.

cheers,
Aldo

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