The language I'm implementing has bignums, and I'm wondering about how much
it costs to use BigInteger for everything vs. having Integer for
fixnums and BigInteger
for fixnums. I'm already committed to boxing all numbers, so it seems
to me that
I might just as well use BigIntegers all the way down. When invoking
Java methods,
of course, I'll have to cast from BigInteger to Integer (or Long).
I did a little profiling, which suggested that on the 1.6 JVM the cost of using
BigIntegers in the Integer range is a small constant factor, 3-4, presumably
because of the sign-magnitude rather than two's complement representation.
I've attached the (trivial) program, which uses autoboxing.
Any thoughts?
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import java.math.BigInteger;
import java.util.Random;
class Foo {
public static void main(String[] argv) {
Random r = new Random();
int s = Integer.parseInt(argv[0]);
Integer[] small = new Integer[s];
BigInteger[] big = new BigInteger[s];
for (int i = 0; i < s; i++) {
int j = r.nextInt();
small[i] = j;
big[i] = new BigInteger(Integer.toString(j));
}
long t1 = System.currentTimeMillis();
for (int i = 0; i < s; i++) {
for (int j = 0; j < s; j++) {
Integer k = small[i] * small[j];
}
}
long t2 = System.currentTimeMillis();
for (int i = 0; i < s; i++) {
for (int j = 0; j < s; j++) {
BigInteger k = big[i].multiply(big[j]);
}
}
long t3 = System.currentTimeMillis();
System.out.println((t3 - t2) / (t2 - t1));
}
}
