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/* ====================================================================
   Licensed to the Apache Software Foundation (ASF) under one or more
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   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

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package org.apache.poi.ss.util;

import java.math.BigInteger;

final class MutableFPNumber {


	// TODO - what about values between (1014-0.5) and (1014-0.05) ?
	/**
	 * The minimum value in 'Base-10 normalised form'.
* When {@link #_binaryExponent} == 46 this is the the minimum {@link #_frac} value * (1014-0.05) * 2^17 *
* Values between (1014-0.05) and 1014 will be represented as '1' * followed by 14 zeros. * Values less than (1014-0.05) will get shifted by one more power of 10 * * This frac value rounds to '1' followed by fourteen zeros with an incremented decimal exponent */ private static final BigInteger BI_MIN_BASE = new BigInteger("0B5E620F47FFFE666", 16); /** * For 'Base-10 normalised form'
* The maximum {@link #_frac} value when {@link #_binaryExponent} == 49 * (10^15-0.5) * 2^14 */ private static final BigInteger BI_MAX_BASE = new BigInteger("0E35FA9319FFFE000", 16); /** * Width of a long */ private static final int C_64 = 64; /** * Minimum precision after discarding whole 32-bit words from the significand */ private static final int MIN_PRECISION = 72; private BigInteger _significand; private int _binaryExponent; public MutableFPNumber(BigInteger frac, int binaryExponent) { _significand = frac; _binaryExponent = binaryExponent; } public MutableFPNumber copy() { return new MutableFPNumber(_significand, _binaryExponent); } public void normalise64bit() { int oldBitLen = _significand.bitLength(); int sc = oldBitLen - C_64; if (sc == 0) { return; } if (sc < 0) { throw new IllegalStateException("Not enough precision"); } _binaryExponent += sc; if (sc > 32) { int highShift = (sc-1) & 0xFFFFE0; _significand = _significand.shiftRight(highShift); sc -= highShift; oldBitLen -= highShift; } if (sc < 1) { throw new IllegalStateException(); } _significand = Rounder.round(_significand, sc); if (_significand.bitLength() > oldBitLen) { sc++; _binaryExponent++; } _significand = _significand.shiftRight(sc); } public int get64BitNormalisedExponent() { return _binaryExponent + _significand.bitLength() - C_64; } public boolean isBelowMaxRep() { int sc = _significand.bitLength() - C_64; return _significand.compareTo(BI_MAX_BASE.shiftLeft(sc)) < 0; } public boolean isAboveMinRep() { int sc = _significand.bitLength() - C_64; return _significand.compareTo(BI_MIN_BASE.shiftLeft(sc)) > 0; } public NormalisedDecimal createNormalisedDecimal(int pow10) { // missingUnderBits is (0..3) int missingUnderBits = _binaryExponent-39; int fracPart = (_significand.intValue() << missingUnderBits) & 0xFFFF80; long wholePart = _significand.shiftRight(C_64-_binaryExponent-1).longValue(); return new NormalisedDecimal(wholePart, fracPart, pow10); } public void multiplyByPowerOfTen(int pow10) { TenPower tp = TenPower.getInstance(Math.abs(pow10)); if (pow10 < 0) { mulShift(tp._divisor, tp._divisorShift); } else { mulShift(tp._multiplicand, tp._multiplierShift); } } private void mulShift(BigInteger multiplicand, int multiplierShift) { _significand = _significand.multiply(multiplicand); _binaryExponent += multiplierShift; // check for too much precision int sc = (_significand.bitLength() - MIN_PRECISION) & 0xFFFFFFE0; // mask makes multiples of 32 which optimises BigInteger.shiftRight if (sc > 0) { // no need to round because we have at least 8 bits of extra precision _significand = _significand.shiftRight(sc); _binaryExponent += sc; } } private static final class Rounder { private static final BigInteger[] HALF_BITS; static { BigInteger[] bis = new BigInteger[33]; long acc=1; for (int i = 1; i < bis.length; i++) { bis[i] = BigInteger.valueOf(acc); acc <<=1; } HALF_BITS = bis; } /** * @param nBits number of bits to shift right */ public static BigInteger round(BigInteger bi, int nBits) { if (nBits < 1) { return bi; } return bi.add(HALF_BITS[nBits]); } } /** * Holds values for quick multiplication and division by 10 */ private static final class TenPower { private static final BigInteger FIVE = new BigInteger("5"); private static final TenPower[] _cache = new TenPower[350]; public final BigInteger _multiplicand; public final BigInteger _divisor; public final int _divisorShift; public final int _multiplierShift; private TenPower(int index) { BigInteger fivePowIndex = FIVE.pow(index); int bitsDueToFiveFactors = fivePowIndex.bitLength(); int px = 80 + bitsDueToFiveFactors; BigInteger fx = BigInteger.ONE.shiftLeft(px).divide(fivePowIndex); int adj = fx.bitLength() - 80; _divisor = fx.shiftRight(adj); bitsDueToFiveFactors -= adj; _divisorShift = -(bitsDueToFiveFactors+index+80); int sc = fivePowIndex.bitLength() - 68; if (sc > 0) { _multiplierShift = index + sc; _multiplicand = fivePowIndex.shiftRight(sc); } else { _multiplierShift = index; _multiplicand = fivePowIndex; } } static TenPower getInstance(int index) { TenPower result = _cache[index]; if (result == null) { result = new TenPower(index); _cache[index] = result; } return result; } } public ExpandedDouble createExpandedDouble() { return new ExpandedDouble(_significand, _binaryExponent); } }




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