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[QUOTE="Wolfgang Nádasi-Donner, post: 4470767"]
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:

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
user     system      total        real

Bignum      3.856000   0.000000   3.856000 (  3.946000)
Fixnum      7.861000   0.020000   7.881000 (  8.081000)

Further investigations leads to the responsible C 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));
}
return rb_num_coerce_bin(x, y);  // <-- das dauert
}

/* vs. */
VALUE
rb_big_pow(x, y)
VALUE x, y;
{
double d;
long yy;

if (y == INT2FIX(0)) return INT2FIX(1);
switch (TYPE(y)) {
case T_FLOAT:  // <-- das geht schnell
d = RFLOAT(y)->value;
break;

case T_BIGNUM:
...

case T_FIXNUM:
...

default:
return rb_num_coerce_bin(x, y);
}
return rb_float_new(pow(rb_big2dbl(x), d));
}

Is it possible to put this Mail to right place for "Ruby Problem Reports". I didn't find out the right place.

Best regards, Wolfgang Nádasi-Donner
[/QUOTE]

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