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/**********************************************************************
* $Id: CommonBits.cpp,v 1.2 2004/07/02 13:28:29 strk Exp $
*
* GEOS - Geometry Engine Open Source
* http://geos.refractions.net
*
* 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.
*
**********************************************************************
* $Log: CommonBits.cpp,v $
* Revision 1.2 2004/07/02 13:28:29 strk
* Fixed all #include lines to reflect headers layout change.
* Added client application build tips in README.
*
* Revision 1.1 2004/04/10 22:41:25 ybychkov
* "precision" upgraded to JTS 1.4
*
*
**********************************************************************/
#include <geos/precision.h>
namespace geos {
/**
* Computes the bit pattern for the sign and exponent of a
* double-precision number.
* @param num
* @return the bit pattern for the sign and exponent
*/
int64 CommonBits::signExpBits(int64 num){
return num >> 52;
}
/**
* This computes the number of common most-significant bits in the mantissas
* of two double-precision numbers.
* It does not count the hidden bit, which is always 1.
* It does not determine whether the numbers have the same exponent - if they do
* not, the value computed by this function is meaningless.
* @param db
* @return the number of common most-significant mantissa bits
*/
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;
}
/**
* Zeroes the lower n bits of a bitstring.
* @param bits the bitstring to alter
* @param i the number of bits to zero
* @return the zeroed bitstring
*/
int64 CommonBits::zeroLowerBits(int64 bits, int nBits){
int64 invMask = (1<< nBits)-1;
int64 mask = ~ invMask;
int64 zeroed = bits & mask;
return zeroed;
}
/**
* Extracts the i'th bit of a bitstring.
* @param bits the bitstring to extract from
* @param i the bit to extract
* @return the value of the extracted bit
*/
int CommonBits::getBit(int64 bits, int i){
int64 mask = (1 << i);
return (bits & mask) != 0 ? 1 : 0;
}
CommonBits::CommonBits() {
isFirst = true;
commonMantissaBitsCount = 53;
commonBits = 0;
}
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));
}
double CommonBits::getCommon(){
return (double)commonBits;
}
///**
//* A representation of the Double bits formatted for easy readability
//*/
//String toString(int64 bits)
//{
//double x = Double.int64BitsToDouble(bits);
//String numStr = int64.toBinaryString(bits);
//String padStr = "0000000000000000000000000000000000000000000000000000000000000000" + numStr;
//String bitStr = padStr.substring(padStr.length() - 64);
//String str = bitStr.substring(0, 1) + " "
//+ bitStr.substring(1, 12) + "(exp) "
//+ bitStr.substring(12)
//+ " [ " + x + " ]";
//return str;
//}
}
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