Below are some thoughts WRT C static vars and Perl6 INIT blocks.
Comments welcome,
leo
Supporting C static storage
There are some related Perl6 features, namely INIT and FIRST closure
traits [1], which aren't really covered by Parrot yet.
Parrot supports INIT blocks via :immediate, which allows e.g.
translation of:
constant Num pi = { atan(1,1)*4 }; # [2]
But C statics can of course change. The problems is, where to
store the static variable, especially native integers.
double gen_random(double max) { # [3]
static long last = 42;
...
}
We could use closures, coroutines [4], or globals. The former provide
a persistent register frame, where the static can be kept. Translating
a sub with a C static to a coroutine seems to be a bit unnatural
though. And all these solutions are a bit slow and lexicals/globals
are only providing PMC support.
I think, we should use the constant table and allow storing into
the constant table.
E.g.
.static int last = 42 # ldc_i_ic
(We can't use the C<set_i_ic> opcode, as this is loading constants
from the bytecode, which, when mmaped, is readonly and doesn't allow
storing)
last += 10 # add_i_ic / set_ic_i
.static float f = 3.14 # set_n_nc
f += 2.0 # add_n_nc / set_nc_n
f = 5.0 # set_n_nc / set_nc_n
.static .Integer i = "42" # set_p_pc
The 'static' variables are therefore working mostly like constants,
except that they are modifyable. One difference is of course, that
there would be no constant folding, each .static needs a distinct
storage in the constant table.
We'd need a few new opcodes:
ldc_i_ic # load int constant from constant table
set_ic_i # store int into constant table
set_nc_n # store num
assign_pc_p # assign to PMC static value
And maybe some permutations like set_pc_i.
What do you think?
leo
[1] S04 / Closure traits
[2] # t/pmc/sub_38.pir
.sub make_pi :immediate, :anon
$N0 = atan 1.0, 1.0
$N0 *= 4
$P0 = new .Float
$P0 = $N0
.return ($P0)
.end
.sub main :main
.const .Sub pi = "make_pi"
print pi
print "\n"
.end
[3]
http://shootout.alioth.debian.org/sandbox/benchmark.php?test=random&lang=icc&id=0
[4] examples/shootout/random.pir
