Charles Mills
5/18/2005 3:48:00 PM
Wolfgang Nádasi-Donner wrote:
> The german Ruby forum recognized a strange behaviour of the Fixnum
class.
>
> In exponentation Fixnum is much slower than Bignum, which lets us
assume, that some kind of a problem occurs
> in the implementation. Example:
>
> >>>>> Code (Ruby) >>>>>
>
> require 'benchmark'
>
> N = 10**6
> B = 65891264863465298234965902602612457060348499377
> F = 4628
>
> Benchmark.bmbm(10) do |bm|
> bm.report('Bignum') do N.times do
> B ** 0.5
> end end
>
> bm.report('Fixnum') do N.times do
> F ** 0.5
> end end
> end
>
> >>>>> Result >>>>>
> user system total real
>
> Bignum 3.856000 0.000000 3.856000 ( 3.946000)
> Fixnum 7.861000 0.020000 7.881000 ( 8.081000)
>
> >>>>> End of Example >>>>>
>
> Further investigations leads to the responsible C code:
>
> >>>>> Code (C) >>>>>
>
> static VALUE
> fix_pow(x, y)
> VALUE x, y;
> {
> if (FIXNUM_P(y)) {
> long a, b;
>
> b = FIX2LONG(y);
> if (b == 0) return INT2FIX(1);
> if (b == 1) return x;
> a = FIX2LONG(x);
> if (b > 0) {
> return rb_big_pow(rb_int2big(a), y);
> }
> return rb_float_new(pow((double)a, (double)b));
> }
> return rb_num_coerce_bin(x, y); // <-- das dauert
> }
You chould change the above code to and it should solve the speed
problem. untested code:
static VALUE
fix_pow(x, y)
VALUE x, y;
{
if (FIXNUM_P(y)) {
long a, b;
b = FIX2LONG(y);
if (b == 0) return INT2FIX(1);
if (b == 1) return x;
a = FIX2LONG(x);
if (b > 0) {
return rb_big_pow(rb_int2big(a), y);
}
return rb_float_new(pow((double)a, (double)b));
} else if (TYPE(y) == T_FLOAT) {
long a = FIX2LONG(x);
return rb_float_new(pow((double)a, RFLOAT(y)->value));
}
return rb_num_coerce_bin(x, y); // <-- das dauert
}
-Charlie