/**********************************************************************
 *
 * GEOS - Geometry Engine Open Source
 * http://geos.osgeo.org
 *
 * Copyright (C) 2005-2006 Refractions Research Inc.
 * Copyright (C) 2001-2002 Vivid Solutions Inc.
 *
 * This is free software; you can redistribute and/or modify it under
 * the terms of the GNU Lesser General Public Licence as published
 * by the Free Software Foundation.
 * See the COPYING file for more information.
 *
 **********************************************************************/

#include <geos/platform.h> // for int64
#include <geos/precision/CommonBits.h>

namespace geos {
namespace precision { // geos.precision

/*static public*/
int64
CommonBits::signExpBits(int64 num)
{
	return num >> 52;
}

/*static public*/
int
CommonBits::numCommonMostSigMantissaBits(int64 num1, int64 num2)
{
	int count = 0;
	for (int i = 52; i >= 0; i--){
		if (getBit(num1, i) != getBit(num2, i))
			return count;
		count++;
	}
	return 52;
}

/*static public*/
int64
CommonBits::zeroLowerBits(int64 bits, int nBits)
{
	if (nBits >= 64 || nBits < 0) return 0;
	int64 bits_ = static_cast<int64>(bits);
	int64 invMask = (1ull << nBits) - 1;
	int64 mask = ~ invMask;
	int64 zeroed = bits_ & mask;
	return static_cast<int64>(zeroed);
}

/*static public*/
int
CommonBits::getBit(int64 bits, int i)
{
	int64 mask = (1ull << i);
	return (bits & mask) != 0 ? 1 : 0;
}

/*public*/
CommonBits::CommonBits() {
	isFirst = true;
	commonMantissaBitsCount = 53;
	commonBits = 0;
}

/*public*/
void
CommonBits::add(double num)
{
	int64 numBits=(int64)num;
	if (isFirst) {
		commonBits = numBits;
		commonSignExp = signExpBits(commonBits);
		isFirst = false;
		return;
	}
	int64 numSignExp = signExpBits(numBits);
	if (numSignExp != commonSignExp) {
		commonBits = 0;
		return;
	}
	//    System.out.println(toString(commonBits));
	//    System.out.println(toString(numBits));
	commonMantissaBitsCount = numCommonMostSigMantissaBits(commonBits, numBits);
	commonBits = zeroLowerBits(commonBits, 64 - (12 + commonMantissaBitsCount));
	//    System.out.println(toString(commonBits));
}

/*public*/
double
CommonBits::getCommon()
{
	return (double)commonBits;
}

} // namespace geos.precision
} // namespace geos
