| /* |
| * 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 com.google.common.math; |
| |
| 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 com.google.common.annotations.GwtIncompatible; |
| import com.google.common.annotations.VisibleForTesting; |
| import java.math.BigInteger; |
| |
| /** |
| * Utilities for {@code double} primitives. |
| * |
| * @author Louis Wasserman |
| */ |
| @GwtIncompatible |
| final class DoubleUtils { |
| private DoubleUtils() {} |
| |
| static double nextDown(double d) { |
| return -Math.nextUp(-d); |
| } |
| |
| // 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; |
| |
| static final int SIGNIFICAND_BITS = 52; |
| |
| 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 long getSignificand(double d) { |
| checkArgument(isFinite(d), "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); |
| } |
| |
| 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. */ |
| static double ensureNonNegative(double value) { |
| checkArgument(!isNaN(value)); |
| if (value > 0.0) { |
| return value; |
| } else { |
| return 0.0; |
| } |
| } |
| |
| @VisibleForTesting static final long ONE_BITS = 0x3ff0000000000000L; |
| } |