/*

 * Copyright (c) 1998, 2017, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package java.lang;

/**

 * Port of the "Freely Distributable Math Library", version 5.3, from

 * C to Java.

 *

 * <p>The C version of fdlibm relied on the idiom of pointer aliasing

 * a 64-bit double floating-point value as a two-element array of

 * 32-bit integers and reading and writing the two halves of the

 * double independently. This coding pattern was problematic to C

 * optimizers and not directly expressible in Java. Therefore, rather

 * than a memory level overlay, if portions of a double need to be

 * operated on as integer values, the standard library methods for

 * bitwise floating-point to integer conversion,

 * Double.longBitsToDouble and Double.doubleToRawLongBits, are directly

 * or indirectly used.

 *

 * <p>The C version of fdlibm also took some pains to signal the

 * correct IEEE 754 exceptional conditions divide by zero, invalid,

 * overflow and underflow. For example, overflow would be signaled by

 * {@code huge * huge} where {@code huge} was a large constant that

 * would overflow when squared. Since IEEE floating-point exceptional

 * handling is not supported natively in the JVM, such coding patterns

 * have been omitted from this port. For example, rather than {@code

 * return huge * huge}, this port will use {@code return INFINITY}.

 *

 * <p>Various comparison and arithmetic operations in fdlibm could be

 * done either based on the integer view of a value or directly on the

 * floating-point representation. Which idiom is faster may depend on

 * platform specific factors. However, for code clarity if no other

 * reason, this port will favor expressing the semantics of those

 * operations in terms of floating-point operations when convenient to

 * do so.

 */

class FdLibm {

    // Constants used by multiple algorithms

    private static final double INFINITY = Double.POSITIVE_INFINITY;

    private FdLibm() {

        throw new UnsupportedOperationException("No FdLibm instances for you.");

    }

    /**

     * Return the low-order 32 bits of the double argument as an int.

     */

    private static int __LO(double x) {

        long transducer = Double.doubleToRawLongBits(x);

        return (int)transducer;

    }

    /**

     * Return a double with its low-order bits of the second argument

     * and the high-order bits of the first argument..

     */

    private static double __LO(double x, int low) {

        long transX = Double.doubleToRawLongBits(x);

        return Double.longBitsToDouble((transX & 0xFFFF_FFFF_0000_0000L) |

                                       (low    & 0x0000_0000_FFFF_FFFFL));

    }

    /**

     * Return the high-order 32 bits of the double argument as an int.

     */

    private static int __HI(double x) {

        long transducer = Double.doubleToRawLongBits(x);

        return (int)(transducer >> 32);

    }

    /**

     * Return a double with its high-order bits of the second argument

     * and the low-order bits of the first argument..

     */

    private static double __HI(double x, int high) {

        long transX = Double.doubleToRawLongBits(x);

        return Double.longBitsToDouble((transX & 0x0000_0000_FFFF_FFFFL) |

                                       ( ((long)high)) << 32 );

    }

    /**

     * cbrt(x)

     * Return cube root of x

     */

    public static class Cbrt {

        // unsigned

        private static final int B1 = 715094163; /* B1 = (682-0.03306235651)*2**20 */

        private static final int B2 = 696219795; /* B2 = (664-0.03306235651)*2**20 */

        private static final double C =  0x1.15f15f15f15f1p-1; //   19/35   ~= 5.42857142857142815906e-01

        private static final double D = -0x1.691de2532c834p-1; // -864/1225 ~= 7.05306122448979611050e-01

        private static final double E =  0x1.6a0ea0ea0ea0fp0;  //   99/70   ~= 1.41428571428571436819e+00

        private static final double F =  0x1.9b6db6db6db6ep0;  //   45/28   ~= 1.60714285714285720630e+00

        private static final double G =  0x1.6db6db6db6db7p-2; //    5/14   ~= 3.57142857142857150787e-01

        private Cbrt() {

            throw new UnsupportedOperationException();

        }

        public static strictfp double compute(double x) {

            double  t = 0.0;

            double sign;

            if (x == 0.0 || !Double.isFinite(x))

                return x; // Handles signed zeros properly

            sign = (x < 0.0) ? -1.0:  1.0;

            x = Math.abs(x);   // x <- |x|

            // Rough cbrt to 5 bits

            if (x < 0x1.0p-1022) {     // subnormal number

                t = 0x1.0p54;          // set t= 2**54

                t *= x;

                t = __HI(t, __HI(t)/3 + B2);

            } else {

                int hx = __HI(x);           // high word of x

                t = __HI(t, hx/3 + B1);

            }

            // New cbrt to 23 bits, may be implemented in single precision

            double  r, s, w;

            r = t * t/x;

            s = C + r*t;

            t *= G + F/(s + E + D/s);

            // Chopped to 20 bits and make it larger than cbrt(x)

            t = __LO(t, 0);

            t = __HI(t, __HI(t) + 0x00000001);

            // One step newton iteration to 53 bits with error less than 0.667 ulps

            s = t * t;          // t*t is exact

            r = x / s;

            w = t + t;

            r = (r - t)/(w + r);  // r-s is exact

            t = t + t*r;

            // Restore the original sign bit

            return sign * t;

        }

    }

    /**

     * hypot(x,y)

     *

     * Method :

     *      If (assume round-to-nearest) z = x*x + y*y

     *      has error less than sqrt(2)/2 ulp, than

     *      sqrt(z) has error less than 1 ulp (exercise).

     *

     *      So, compute sqrt(x*x + y*y) with some care as

     *      follows to get the error below 1 ulp:

     *

     *      Assume x > y > 0;

     *      (if possible, set rounding to round-to-nearest)

     *      1. if x > 2y  use

     *              x1*x1 + (y*y + (x2*(x + x1))) for x*x + y*y

     *      where x1 = x with lower 32 bits cleared, x2 = x - x1; else

     *      2. if x <= 2y use

     *              t1*y1 + ((x-y) * (x-y) + (t1*y2 + t2*y))

     *      where t1 = 2x with lower 32 bits cleared, t2 = 2x - t1,

     *      y1= y with lower 32 bits chopped, y2 = y - y1.

     *

     *      NOTE: scaling may be necessary if some argument is too

     *            large or too tiny

     *

     * Special cases:

     *      hypot(x,y) is INF if x or y is +INF or -INF; else

     *      hypot(x,y) is NAN if x or y is NAN.

     *

     * Accuracy:

     *      hypot(x,y) returns sqrt(x^2 + y^2) with error less

     *      than 1 ulp (unit in the last place)

     */

    public static class Hypot {

        public static final double TWO_MINUS_600 = 0x1.0p-600;

        public static final double TWO_PLUS_600  = 0x1.0p+600;

        private Hypot() {

            throw new UnsupportedOperationException();

        }

        public static strictfp double compute(double x, double y) {

            double a = Math.abs(x);

            double b = Math.abs(y);

            if (!Double.isFinite(a) || !Double.isFinite(b)) {

                if (a == INFINITY || b == INFINITY)

                    return INFINITY;

                else

                    return a + b; // Propagate NaN significand bits

            }

            if (b > a) {

                double tmp = a;

                a = b;

                b = tmp;

            }

            assert a >= b;

            // Doing bitwise conversion after screening for NaN allows

            // the code to not worry about the possibility of

            // "negative" NaN values.

            // Note: the ha and hb variables are the high-order

            // 32-bits of a and b stored as integer values. The ha and

            // hb values are used first for a rough magnitude

            // comparison of a and b and second for simulating higher

            // precision by allowing a and b, respectively, to be

            // decomposed into non-overlapping portions. Both of these

            // uses could be eliminated. The magnitude comparison

            // could be eliminated by extracting and comparing the

            // exponents of a and b or just be performing a

            // floating-point divide.  Splitting a floating-point

            // number into non-overlapping portions can be

            // accomplished by judicious use of multiplies and

            // additions. For details see T. J. Dekker, A Floating

            // Point Technique for Extending the Available Precision ,

            // Numerische Mathematik, vol. 18, 1971, pp.224-242 and

            // subsequent work.

            int ha = __HI(a);        // high word of a

            int hb = __HI(b);        // high word of b

            if ((ha - hb) > 0x3c00000) {

                return a + b;  // x / y > 2**60

            }

            int k = 0;

            if (a > 0x1.00000_ffff_ffffp500) {   // a > ~2**500

                // scale a and b by 2**-600

                ha -= 0x25800000;

                hb -= 0x25800000;

                a = a * TWO_MINUS_600;

                b = b * TWO_MINUS_600;

                k += 600;

            }

            double t1, t2;

            if (b < 0x1.0p-500) {   // b < 2**-500

                if (b < Double.MIN_NORMAL) {      // subnormal b or 0 */

                    if (b == 0.0)

                        return a;

                    t1 = 0x1.0p1022;   // t1 = 2^1022

                    b *= t1;

                    a *= t1;

                    k -= 1022;

                } else {            // scale a and b by 2^600

                    ha += 0x25800000;       // a *= 2^600

                    hb += 0x25800000;       // b *= 2^600

                    a = a * TWO_PLUS_600;

                    b = b * TWO_PLUS_600;

                    k -= 600;

                }

            }

            // medium size a and b

            double w = a - b;

            if (w > b) {

                t1 = 0;

                t1 = __HI(t1, ha);

                t2 = a - t1;

                w  = Math.sqrt(t1*t1 - (b*(-b) - t2 * (a + t1)));

            } else {

                double y1, y2;

                a  = a + a;

                y1 = 0;

                y1 = __HI(y1, hb);

                y2 = b - y1;

                t1 = 0;

                t1 = __HI(t1, ha + 0x00100000);

                t2 = a - t1;

                w  = Math.sqrt(t1*y1 - (w*(-w) - (t1*y2 + t2*b)));

            }

            if (k != 0) {

                return Math.powerOfTwoD(k) * w;

            } else

                return w;

        }

    }

    /**

     * Compute x**y

     *                    n

     * Method:  Let x =  2   * (1+f)

     *      1. Compute and return log2(x) in two pieces:

     *              log2(x) = w1 + w2,

     *         where w1 has 53 - 24 = 29 bit trailing zeros.

     *      2. Perform y*log2(x) = n+y' by simulating multi-precision

     *         arithmetic, where |y'| <= 0.5.

     *      3. Return x**y = 2**n*exp(y'*log2)

     *

     * Special cases:

     *      1.  (anything) ** 0  is 1

     *      2.  (anything) ** 1  is itself

     *      3.  (anything) ** NAN is NAN

     *      4.  NAN ** (anything except 0) is NAN

     *      5.  +-(|x| > 1) **  +INF is +INF

     *      6.  +-(|x| > 1) **  -INF is +0

     *      7.  +-(|x| < 1) **  +INF is +0

     *      8.  +-(|x| < 1) **  -INF is +INF

     *      9.  +-1         ** +-INF is NAN

     *      10. +0 ** (+anything except 0, NAN)               is +0

     *      11. -0 ** (+anything except 0, NAN, odd integer)  is +0

     *      12. +0 ** (-anything except 0, NAN)               is +INF

     *      13. -0 ** (-anything except 0, NAN, odd integer)  is +INF

     *      14. -0 ** (odd integer) = -( +0 ** (odd integer) )

     *      15. +INF ** (+anything except 0,NAN) is +INF

     *      16. +INF ** (-anything except 0,NAN) is +0

     *      17. -INF ** (anything)  = -0 ** (-anything)

     *      18. (-anything) ** (integer) is (-1)**(integer)*(+anything**integer)

     *      19. (-anything except 0 and inf) ** (non-integer) is NAN

     *

     * Accuracy:

     *      pow(x,y) returns x**y nearly rounded. In particular

     *                      pow(integer,integer)

     *      always returns the correct integer provided it is

     *      representable.

     */

    public static class Pow {

        private Pow() {

            throw new UnsupportedOperationException();

        }

        public static strictfp double compute(final double x, final double y) {

            double z;

            double r, s, t, u, v, w;

            int i, j, k, n;

            // y == zero: x**0 = 1

            if (y == 0.0)

                return 1.0;

            // +/-NaN return x + y to propagate NaN significands

            if (Double.isNaN(x) || Double.isNaN(y))

                return x + y;

            final double y_abs = Math.abs(y);

            double x_abs   = Math.abs(x);

            // Special values of y

            if (y == 2.0) {

                return x * x;

            } else if (y == 0.5) {

                if (x >= -Double.MAX_VALUE) // Handle x == -infinity later

                    return Math.sqrt(x + 0.0); // Add 0.0 to properly handle x == -0.0

            } else if (y_abs == 1.0) {        // y is  +/-1

                return (y == 1.0) ? x : 1.0 / x;

            } else if (y_abs == INFINITY) {       // y is +/-infinity

                if (x_abs == 1.0)

                    return  y - y;         // inf**+/-1 is NaN

                else if (x_abs > 1.0) // (|x| > 1)**+/-inf = inf, 0

                    return (y >= 0) ? y : 0.0;

                else                       // (|x| < 1)**-/+inf = inf, 0

                    return (y < 0) ? -y : 0.0;

            }

            final int hx = __HI(x);

            int ix = hx & 0x7fffffff;

            /*

             * When x < 0, determine if y is an odd integer:

             * y_is_int = 0       ... y is not an integer

             * y_is_int = 1       ... y is an odd int

             * y_is_int = 2       ... y is an even int

             */

            int y_is_int  = 0;

            if (hx < 0) {

                if (y_abs >= 0x1.0p53)   // |y| >= 2^53 = 9.007199254740992E15

                    y_is_int = 2; // y is an even integer since ulp(2^53) = 2.0

                else if (y_abs >= 1.0) { // |y| >= 1.0

                    long y_abs_as_long = (long) y_abs;

                    if ( ((double) y_abs_as_long) == y_abs) {

                        y_is_int = 2 -  (int)(y_abs_as_long & 0x1L);

                    }

                }

            }

            // Special value of x

            if (x_abs == 0.0 ||

                x_abs == INFINITY ||

                x_abs == 1.0) {

                z = x_abs;                 // x is +/-0, +/-inf, +/-1

                if (y < 0.0)

                    z = 1.0/z;     // z = (1/|x|)

                if (hx < 0) {

                    if (((ix - 0x3ff00000) | y_is_int) == 0) {

                        z = (z-z)/(z-z); // (-1)**non-int is NaN

                    } else if (y_is_int == 1)

                        z = -1.0 * z;             // (x < 0)**odd = -(|x|**odd)

                }

                return z;

            }

            n = (hx >> 31) + 1;

            // (x < 0)**(non-int) is NaN

            if ((n | y_is_int) == 0)

                return (x-x)/(x-x);

            s = 1.0; // s (sign of result -ve**odd) = -1 else = 1

            if ( (n | (y_is_int - 1)) == 0)

                s = -1.0; // (-ve)**(odd int)

            double p_h, p_l, t1, t2;

            // |y| is huge

            if (y_abs > 0x1.00000_ffff_ffffp31) { // if |y| > ~2**31

                final double INV_LN2   =  0x1.7154_7652_b82fep0;   //  1.44269504088896338700e+00 = 1/ln2

                final double INV_LN2_H =  0x1.715476p0;            //  1.44269502162933349609e+00 = 24 bits of 1/ln2

                final double INV_LN2_L =  0x1.4ae0_bf85_ddf44p-26; //  1.92596299112661746887e-08 = 1/ln2 tail

                // Over/underflow if x is not close to one

                if (x_abs < 0x1.fffff_0000_0000p-1) // |x| < ~0.9999995231628418

                    return (y < 0.0) ? s * INFINITY : s * 0.0;

                if (x_abs > 0x1.00000_ffff_ffffp0)         // |x| > ~1.0

                    return (y > 0.0) ? s * INFINITY : s * 0.0;

                /*

                 * now |1-x| is tiny <= 2**-20, sufficient to compute

                 * log(x) by x - x^2/2 + x^3/3 - x^4/4

                 */

                t = x_abs - 1.0;        // t has 20 trailing zeros

                w = (t * t) * (0.5 - t * (0.3333333333333333333333 - t * 0.25));

                u = INV_LN2_H * t;      // INV_LN2_H has 21 sig. bits

                v =  t * INV_LN2_L - w * INV_LN2;

                t1 = u + v;

                t1 =__LO(t1, 0);

                t2 = v - (t1 - u);

            } else {

                final double CP      =  0x1.ec70_9dc3_a03fdp-1;  //  9.61796693925975554329e-01 = 2/(3ln2)

                final double CP_H    =  0x1.ec709ep-1;           //  9.61796700954437255859e-01 = (float)cp

                final double CP_L    = -0x1.e2fe_0145_b01f5p-28; // -7.02846165095275826516e-09 = tail of CP_H

                double z_h, z_l, ss, s2, s_h, s_l, t_h, t_l;

                n = 0;

                // Take care of subnormal numbers

                if (ix < 0x00100000) {

                    x_abs *= 0x1.0p53; // 2^53 = 9007199254740992.0

                    n -= 53;

                    ix = __HI(x_abs);

                }

                n  += ((ix) >> 20) - 0x3ff;

                j  = ix & 0x000fffff;

                // Determine interval

                ix = j | 0x3ff00000;          // Normalize ix

                if (j <= 0x3988E)

                    k = 0;         // |x| <sqrt(3/2)

                else if (j < 0xBB67A)

                    k = 1;         // |x| <sqrt(3)

                else {

                    k = 0;

                    n += 1;

                    ix -= 0x00100000;

                }

                x_abs = __HI(x_abs, ix);

                // Compute ss = s_h + s_l = (x-1)/(x+1) or (x-1.5)/(x+1.5)

                final double BP[]    = {1.0,

                                       1.5};

                final double DP_H[]  = {0.0,

                                        0x1.2b80_34p-1};        // 5.84962487220764160156e-01

                final double DP_L[]  = {0.0,

                                        0x1.cfde_b43c_fd006p-27};// 1.35003920212974897128e-08

                // Poly coefs for (3/2)*(log(x)-2s-2/3*s**3

                final double L1      =  0x1.3333_3333_33303p-1;  //  5.99999999999994648725e-01

                final double L2      =  0x1.b6db_6db6_fabffp-2;  //  4.28571428578550184252e-01

                final double L3      =  0x1.5555_5518_f264dp-2;  //  3.33333329818377432918e-01

                final double L4      =  0x1.1746_0a91_d4101p-2;  //  2.72728123808534006489e-01

                final double L5      =  0x1.d864_a93c_9db65p-3;  //  2.30660745775561754067e-01

                final double L6      =  0x1.a7e2_84a4_54eefp-3;  //  2.06975017800338417784e-01

                u = x_abs - BP[k];               // BP[0]=1.0, BP[1]=1.5

                v = 1.0 / (x_abs + BP[k]);

                ss = u * v;

                s_h = ss;

                s_h = __LO(s_h, 0);

                // t_h=x_abs + BP[k] High

                t_h = 0.0;

                t_h = __HI(t_h, ((ix >> 1) | 0x20000000) + 0x00080000 + (k << 18) );

                t_l = x_abs - (t_h - BP[k]);

                s_l = v * ((u - s_h * t_h) - s_h * t_l);

                // Compute log(x_abs)

                s2 = ss * ss;

                r = s2 * s2* (L1 + s2 * (L2 + s2 * (L3 + s2 * (L4 + s2 * (L5 + s2 * L6)))));

                r += s_l * (s_h + ss);

                s2  = s_h * s_h;

                t_h = 3.0 + s2 + r;

                t_h = __LO(t_h, 0);

                t_l = r - ((t_h - 3.0) - s2);

                // u+v = ss*(1+...)

                u = s_h * t_h;

                v = s_l * t_h + t_l * ss;