ObjectIDOperations.java
/*
* Copyright (c) 2014 Oracle and/or its affiliates. All rights reserved. This
* code is released under a tri EPL/GPL/LGPL license. You can use it,
* redistribute it and/or modify it under the terms of the:
*
* Eclipse Public License version 1.0
* GNU General Public License version 2
* GNU Lesser General Public License version 2.1
*/
package org.jruby.truffle.runtime;
import com.oracle.truffle.api.ExactMath;
import org.jruby.truffle.runtime.core.RubyBignum;
import java.math.BigInteger;
/**
* <pre>
* Object IDs distribution
*
* We try to respect MRI scheme when it makes sense (Fixnum for the moment).
* Have a look at include/ruby/ruby.h below ruby_special_consts.
*
* Encoding for Fixnum (long):
* ... 0000 = false
* ... 0010 = true
* ... 0100 = nil
*
* ... xxx1 = Fixnum of value (id-1)/2 if -2^62 <= value < 2^62
* ... xxx0 = BasicObject generated id (for id > 4)
*
* Encoding for Bignum:
* ... 0001 | 64-bit long = Fixnum if value < -2^62 or value >= 2^62
* ... 0010 | 64-bit raw double bits = Float
* </pre>
*/
public abstract class ObjectIDOperations {
public static final int FALSE = 0;
public static final int TRUE = 2;
public static final int NIL = 4;
public static final int FIRST_OBJECT_ID = 6;
private static final BigInteger LARGE_FIXNUM_FLAG = BigInteger.ONE.shiftLeft(64);
private static final BigInteger FLOAT_FLAG = BigInteger.ONE.shiftLeft(65);
private static final long SMALL_FIXNUM_MIN = -(1L << 62);
private static final long SMALL_FIXNUM_MAX = (1L << 62) - 1;
// primitive => ID
public static boolean isSmallFixnum(long fixnum) {
// TODO: optimize
return SMALL_FIXNUM_MIN <= fixnum && fixnum <= SMALL_FIXNUM_MAX;
}
public static long smallFixnumToIDOverflow(long fixnum) throws ArithmeticException{
return ExactMath.addExact(ExactMath.multiplyExact(fixnum, 2), 1);
}
public static long smallFixnumToID(long fixnum) {
assert isSmallFixnum(fixnum);
return fixnum * 2 + 1;
}
public static RubyBignum largeFixnumToID(RubyContext context, long fixnum) {
assert !isSmallFixnum(fixnum);
return new RubyBignum(context.getCoreLibrary().getBignumClass(), BigInteger.valueOf(fixnum).or(LARGE_FIXNUM_FLAG));
}
public static RubyBignum floatToID(RubyContext context, double value) {
long bits = Double.doubleToRawLongBits(value);
return new RubyBignum(context.getCoreLibrary().getBignumClass(), BigInteger.valueOf(bits).or(FLOAT_FLAG));
}
// ID => primitive
public static boolean isSmallFixnumID(long id) {
return id % 2 != 0;
}
public static long toFixnum(long id) {
return (id - 1) / 2;
}
public static boolean isLargeFixnumID(RubyBignum id) {
return !id.bigIntegerValue().and(LARGE_FIXNUM_FLAG).equals(BigInteger.ZERO);
}
public static long toFixnum(RubyBignum id) {
return id.longValue();
}
public static boolean isFloatID(RubyBignum id) {
return !id.bigIntegerValue().and(FLOAT_FLAG).equals(BigInteger.ZERO);
}
public static double toFloat(RubyBignum id) {
return Double.longBitsToDouble(id.longValue());
}
}