/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed 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
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package ptolemy.util;

// Remove the dependency on google classes.
//import static com.google.common.base.Preconditions.checkArgument;
import static java.lang.Double.MAX_EXPONENT;
import static java.lang.Double.MIN_EXPONENT;
import static java.lang.Double.POSITIVE_INFINITY;
import static java.lang.Double.doubleToRawLongBits;
import static java.lang.Double.isNaN;
import static java.lang.Double.longBitsToDouble;
import static java.lang.Math.getExponent;

import java.math.BigInteger;

/**
 * Utilities for double primitives.
 *
 * This code is used by ptolemy.actor.util.Time to improve performance.
 *
 * @author Louis Wasserman, based on https://code.google.com/p/guava-libraries/source/browse/guava/src/com/google/common/math/DoubleUtils.java
@version $Id$
@since Ptolemy II 11.0
 */
public final class DoubleUtilities {
    private DoubleUtilities() {
    }

    static double nextDown(double d) {
        return -Math.nextUp(-d);
    }

    static long getSignificand(double d) {
        // Remove check argument and replace with conditionals
        // to remove dependency on google classes.
        //checkArgument(isFinite(d), "not a normal value");
        if (!isFinite(d)) {
            throw new IllegalArgumentException("not a normal value");
        }
        int exponent = getExponent(d);
        long bits = doubleToRawLongBits(d);
        bits &= SIGNIFICAND_MASK;
        return (exponent == MIN_EXPONENT - 1) ? bits << 1 : bits | IMPLICIT_BIT;
    }

    static boolean isFinite(double d) {
        return getExponent(d) <= MAX_EXPONENT;
    }

    static boolean isNormal(double d) {
        return getExponent(d) >= MIN_EXPONENT;
    }

    /*
     * Returns x scaled by a power of 2 such that it is in the range [1, 2). Assumes x is positive,
     * normal, and finite.
     */
    static double scaleNormalize(double x) {
        long significand = doubleToRawLongBits(x) & SIGNIFICAND_MASK;
        return longBitsToDouble(significand | ONE_BITS);
    }

    /** Convert a BigInteger to a double using a fast implementation.
     *  @param x The BigInteger to be converted.
     *  @return the value of the BigInteger as a double.
     */
    public static double bigToDouble(BigInteger x) {
        // This is an extremely fast implementation of BigInteger.doubleValue().  JDK patch pending.
        BigInteger absX = x.abs();
        int exponent = absX.bitLength() - 1;
        // exponent == floor(log2(abs(x)))
        if (exponent < Long.SIZE - 1) {
            return x.longValue();
        } else if (exponent > MAX_EXPONENT) {
            return x.signum() * POSITIVE_INFINITY;
        }

        /*
         * We need the top SIGNIFICAND_BITS + 1 bits, including the "implicit" one bit. To make
         * rounding easier, we pick out the top SIGNIFICAND_BITS + 2 bits, so we have one to help us
         * round up or down. twiceSignifFloor will contain the top SIGNIFICAND_BITS + 2 bits, and
         * signifFloor the top SIGNIFICAND_BITS + 1.
         *
         * It helps to consider the real number signif = absX * 2^(SIGNIFICAND_BITS - exponent).
         */
        int shift = exponent - SIGNIFICAND_BITS - 1;
        long twiceSignifFloor = absX.shiftRight(shift).longValue();
        long signifFloor = twiceSignifFloor >> 1;
        signifFloor &= SIGNIFICAND_MASK; // remove the implied bit

        /*
         * We round up if either the fractional part of signif is strictly greater than 0.5 (which is
         * true if the 0.5 bit is set and any lower bit is set), or if the fractional part of signif is
         * >= 0.5 and signifFloor is odd (which is true if both the 0.5 bit and the 1 bit are set).
         */
        boolean increment = (twiceSignifFloor & 1) != 0
                && ((signifFloor & 1) != 0 || absX.getLowestSetBit() < shift);
        long signifRounded = increment ? signifFloor + 1 : signifFloor;
        long bits = (long) ((exponent + EXPONENT_BIAS)) << SIGNIFICAND_BITS;
        bits += signifRounded;
        /*
         * If signifRounded == 2^53, we'd need to set all of the significand bits to zero and add 1 to
         * the exponent. This is exactly the behavior we get from just adding signifRounded to bits
         * directly.  If the exponent is MAX_DOUBLE_EXPONENT, we round up (correctly) to
         * Double.POSITIVE_INFINITY.
         */
        bits |= x.signum() & SIGN_MASK;
        return longBitsToDouble(bits);
    }

    /**
     * Returns its argument if it is non-negative, zero if it is negative.
     * @param value The value to be checked.
     * @return If value is non-negative, return the value.  If the value
     * is negative, then return zero.
     */
    static double ensureNonNegative(double value) {
        // Remove check argument and replace with conditionals
        // to remove dependency on google classes.
        //checkArgument(!isNaN(value));
        if (isNaN(value)) {
            throw new IllegalArgumentException("not a number");
        }
        if (value > 0.0) {
            return value;
        } else {
            return 0.0;
        }
    }

    ///////////////////////////////////////////////////////////////////
    ////                    static variables                      ////

    // The mask for the significand, according to the {@link
    // Double#doubleToRawLongBits(double)} spec.
    static final long SIGNIFICAND_MASK = 0x000fffffffffffffL;

    // The mask for the exponent, according to the {@link
    // Double#doubleToRawLongBits(double)} spec.
    static final long EXPONENT_MASK = 0x7ff0000000000000L;

    // The mask for the sign, according to the {@link
    // Double#doubleToRawLongBits(double)} spec.
    static final long SIGN_MASK = 0x8000000000000000L;

    // The significands bits
    static final int SIGNIFICAND_BITS = 52;

    // The exponent bias
    static final int EXPONENT_BIAS = 1023;

    // The implicit 1 bit that is omitted in significands of normal doubles.
    static final long IMPLICIT_BIT = SIGNIFICAND_MASK + 1;

    ///////////////////////////////////////////////////////////////////
    ////                      static private variables            ////

    private static final long ONE_BITS = doubleToRawLongBits(1.0);
}