/*
 *  Copyright (C) 1999-2000 Harri Porten (porten@kde.org)
 *  Copyright (C) 2007, 2008, 2013 Apple Inc. All Rights Reserved.
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2 of the License, or (at your option) any later version.
 *
 *  This library 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
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 */

#include "config.h"
#include "MathObject.h"

#include "Lookup.h"
#include "ObjectPrototype.h"
#include "JSCInlines.h"
#include <time.h>
#include <wtf/Assertions.h>
#include <wtf/MathExtras.h>
#include <wtf/RandomNumber.h>
#include <wtf/RandomNumberSeed.h>
#include <wtf/Vector.h>

namespace JSC {

STATIC_ASSERT_IS_TRIVIALLY_DESTRUCTIBLE(MathObject);

static EncodedJSValue JSC_HOST_CALL mathProtoFuncAbs(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncACos(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncACosh(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncASin(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncASinh(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncATan(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncATanh(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncATan2(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncCbrt(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncCeil(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncCos(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncCosh(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncExp(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncExpm1(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncFloor(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncFround(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncHypot(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncLog(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncLog1p(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncLog10(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncLog2(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncMax(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncMin(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncPow(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncRandom(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncRound(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncSign(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncSin(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncSinh(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncSqrt(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncTan(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncTanh(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncTrunc(ExecState*);
static EncodedJSValue JSC_HOST_CALL mathProtoFuncIMul(ExecState*);

}

namespace JSC {

const ClassInfo MathObject::s_info = { "Math", &Base::s_info, 0, CREATE_METHOD_TABLE(MathObject) };

MathObject::MathObject(VM& vm, Structure* structure)
    : JSNonFinalObject(vm, structure)
{
}

void MathObject::finishCreation(VM& vm, JSGlobalObject* globalObject)
{
    Base::finishCreation(vm);
    ASSERT(inherits(info()));

    putDirectWithoutTransition(vm, Identifier(&vm, "E"), jsNumber(exp(1.0)), DontDelete | DontEnum | ReadOnly);
    putDirectWithoutTransition(vm, Identifier(&vm, "LN2"), jsNumber(log(2.0)), DontDelete | DontEnum | ReadOnly);
    putDirectWithoutTransition(vm, Identifier(&vm, "LN10"), jsNumber(log(10.0)), DontDelete | DontEnum | ReadOnly);
    putDirectWithoutTransition(vm, Identifier(&vm, "LOG2E"), jsNumber(1.0 / log(2.0)), DontDelete | DontEnum | ReadOnly);
    putDirectWithoutTransition(vm, Identifier(&vm, "LOG10E"), jsNumber(0.4342944819032518), DontDelete | DontEnum | ReadOnly);
    putDirectWithoutTransition(vm, Identifier(&vm, "PI"), jsNumber(piDouble), DontDelete | DontEnum | ReadOnly);
    putDirectWithoutTransition(vm, Identifier(&vm, "SQRT1_2"), jsNumber(sqrt(0.5)), DontDelete | DontEnum | ReadOnly);
    putDirectWithoutTransition(vm, Identifier(&vm, "SQRT2"), jsNumber(sqrt(2.0)), DontDelete | DontEnum | ReadOnly);

    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "abs"), 1, mathProtoFuncAbs, AbsIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "acos"), 1, mathProtoFuncACos, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "asin"), 1, mathProtoFuncASin, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "atan"), 1, mathProtoFuncATan, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "acosh"), 1, mathProtoFuncACosh, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "asinh"), 1, mathProtoFuncASinh, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "atanh"), 1, mathProtoFuncATanh, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "atan2"), 2, mathProtoFuncATan2, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "cbrt"), 1, mathProtoFuncCbrt, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "ceil"), 1, mathProtoFuncCeil, CeilIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "cos"), 1, mathProtoFuncCos, CosIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "cosh"), 1, mathProtoFuncCosh, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "exp"), 1, mathProtoFuncExp, ExpIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "expm1"), 1, mathProtoFuncExpm1, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "floor"), 1, mathProtoFuncFloor, FloorIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "fround"), 1, mathProtoFuncFround, FRoundIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "hypot"), 2, mathProtoFuncHypot, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "log"), 1, mathProtoFuncLog, LogIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "log10"), 1, mathProtoFuncLog10, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "log1p"), 1, mathProtoFuncLog1p, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "log2"), 1, mathProtoFuncLog2, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "max"), 2, mathProtoFuncMax, MaxIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "min"), 2, mathProtoFuncMin, MinIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "pow"), 2, mathProtoFuncPow, PowIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "random"), 0, mathProtoFuncRandom, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "round"), 1, mathProtoFuncRound, RoundIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "sign"), 1, mathProtoFuncSign, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "sin"), 1, mathProtoFuncSin, SinIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "sinh"), 1, mathProtoFuncSinh, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "sqrt"), 1, mathProtoFuncSqrt, SqrtIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "tan"), 1, mathProtoFuncTan, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "tanh"), 1, mathProtoFuncTanh, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "trunc"), 1, mathProtoFuncTrunc, NoIntrinsic, DontEnum | Function);
    putDirectNativeFunctionWithoutTransition(vm, globalObject, Identifier(&vm, "imul"), 1, mathProtoFuncIMul, IMulIntrinsic, DontEnum | Function);
}

// ------------------------------ Functions --------------------------------

EncodedJSValue JSC_HOST_CALL mathProtoFuncAbs(ExecState* exec)
{
    return JSValue::encode(jsNumber(fabs(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncACos(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(acos(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncASin(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(asin(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncATan(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(atan(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncATan2(ExecState* exec)
{
    double arg0 = exec->argument(0).toNumber(exec);
    double arg1 = exec->argument(1).toNumber(exec);
    return JSValue::encode(jsDoubleNumber(atan2(arg0, arg1)));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncCeil(ExecState* exec)
{
    return JSValue::encode(jsNumber(ceil(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncCos(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(cos(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncExp(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(exp(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncFloor(ExecState* exec)
{
    return JSValue::encode(jsNumber(floor(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncHypot(ExecState* exec)
{
    unsigned argsCount = exec->argumentCount();
    double max = 0;
    Vector<double, 8> args;
    args.reserveInitialCapacity(argsCount);
    for (unsigned i = 0; i < argsCount; ++i) {
        args.uncheckedAppend(exec->uncheckedArgument(i).toNumber(exec));
        if (exec->hadException())
            return JSValue::encode(jsNull());
        if (std::isinf(args[i]))
            return JSValue::encode(jsDoubleNumber(+std::numeric_limits<double>::infinity()));
        max = std::max(fabs(args[i]), max);
    }
    if (!max)
        max = 1;
    // Kahan summation algorithm significantly reduces the numerical error in the total obtained.
    double sum = 0;
    double compensation = 0;
    for (double argument : args) {
        double scaledArgument = argument / max;
        double summand = scaledArgument * scaledArgument - compensation;
        double preliminary = sum + summand;
        compensation = (preliminary - sum) - summand;
        sum = preliminary;
    }
    return JSValue::encode(jsDoubleNumber(sqrt(sum) * max));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncLog(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(log(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncMax(ExecState* exec)
{
    unsigned argsCount = exec->argumentCount();
    double result = -std::numeric_limits<double>::infinity();
    for (unsigned k = 0; k < argsCount; ++k) {
        double val = exec->uncheckedArgument(k).toNumber(exec);
        if (std::isnan(val)) {
            result = PNaN;
        } else if (val > result || (!val && !result && !std::signbit(val)))
            result = val;
    }
    return JSValue::encode(jsNumber(result));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncMin(ExecState* exec)
{
    unsigned argsCount = exec->argumentCount();
    double result = +std::numeric_limits<double>::infinity();
    for (unsigned k = 0; k < argsCount; ++k) {
        double val = exec->uncheckedArgument(k).toNumber(exec);
        if (std::isnan(val)) {
            result = PNaN;
        } else if (val < result || (!val && !result && std::signbit(val)))
            result = val;
    }
    return JSValue::encode(jsNumber(result));
}

#if PLATFORM(IOS) && CPU(ARM_THUMB2)

static double fdlibmPow(double x, double y);

static ALWAYS_INLINE bool isDenormal(double x)
{
        static const uint64_t signbit = 0x8000000000000000ULL;
        static const uint64_t minNormal = 0x0001000000000000ULL;
        return (bitwise_cast<uint64_t>(x) & ~signbit) - 1 < minNormal - 1;
}

static ALWAYS_INLINE bool isEdgeCase(double x)
{
        static const uint64_t signbit = 0x8000000000000000ULL;
        static const uint64_t infinity = 0x7fffffffffffffffULL;
        return (bitwise_cast<uint64_t>(x) & ~signbit) - 1 >= infinity - 1;
}

static ALWAYS_INLINE double mathPow(double x, double y)
{
    if (!isDenormal(x) && !isDenormal(y)) {
        double libmResult = pow(x,y);
        if (libmResult || isEdgeCase(x) || isEdgeCase(y))
            return libmResult;
    }
    return fdlibmPow(x,y);
}

#else

ALWAYS_INLINE double mathPow(double x, double y)
{
    return pow(x, y);
}

#endif

EncodedJSValue JSC_HOST_CALL mathProtoFuncPow(ExecState* exec)
{
    // ECMA 15.8.2.1.13

    double arg = exec->argument(0).toNumber(exec);
    double arg2 = exec->argument(1).toNumber(exec);

    if (std::isnan(arg2))
        return JSValue::encode(jsNaN());
    if (std::isinf(arg2) && fabs(arg) == 1)
        return JSValue::encode(jsNaN());
    return JSValue::encode(jsNumber(mathPow(arg, arg2)));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncRandom(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(exec->lexicalGlobalObject()->weakRandomNumber()));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncRound(ExecState* exec)
{
    double arg = exec->argument(0).toNumber(exec);
    double integer = ceil(arg);
    return JSValue::encode(jsNumber(integer - (integer - arg > 0.5)));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncSign(ExecState* exec)
{
    double arg = exec->argument(0).toNumber(exec);
    if (std::isnan(arg))
        return JSValue::encode(jsNaN());
    if (!arg)
        return JSValue::encode(std::signbit(arg) ? jsNumber(-0.0) : jsNumber(0));
    return JSValue::encode(jsNumber(std::signbit(arg) ? -1 : 1));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncSin(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(sin(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncSqrt(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(sqrt(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncTan(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(tan(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncIMul(ExecState* exec)
{
    int32_t left = exec->argument(0).toInt32(exec);
    if (exec->hadException())
        return JSValue::encode(jsNull());
    int32_t right = exec->argument(1).toInt32(exec);
    return JSValue::encode(jsNumber(left * right));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncACosh(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(acosh(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncASinh(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(asinh(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncATanh(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(atanh(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncCbrt(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(cbrt(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncCosh(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(cosh(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncExpm1(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(expm1(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncFround(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(static_cast<float>(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncLog1p(ExecState* exec)
{
    double value = exec->argument(0).toNumber(exec);
    if (value == 0)
        return JSValue::encode(jsDoubleNumber(value));
    return JSValue::encode(jsDoubleNumber(log1p(value)));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncLog10(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(log10(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncLog2(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(log2(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncSinh(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(sinh(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncTanh(ExecState* exec)
{
    return JSValue::encode(jsDoubleNumber(tanh(exec->argument(0).toNumber(exec))));
}

EncodedJSValue JSC_HOST_CALL mathProtoFuncTrunc(ExecState*exec)
{
    return JSValue::encode(jsNumber(exec->argument(0).toIntegerPreserveNaN(exec)));
}


#if PLATFORM(IOS) && CPU(ARM_THUMB2)

// The following code is taken from netlib.org:
//   http://www.netlib.org/fdlibm/fdlibm.h
//   http://www.netlib.org/fdlibm/e_pow.c
//   http://www.netlib.org/fdlibm/s_scalbn.c
//
// And was originally distributed under the following license:

/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice 
 * is preserved.
 * ====================================================
 */
/*
 * ====================================================
 * Copyright (C) 2004 by Sun Microsystems, Inc. All rights reserved.
 *
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice 
 * is preserved.
 * ====================================================
 */

/* __ieee754_pow(x,y) return 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 muti-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.
 *
 * Constants :
 * The hexadecimal values are the intended ones for the following 
 * constants. The decimal values may be used, provided that the 
 * compiler will convert from decimal to binary accurately enough 
 * to produce the hexadecimal values shown.
 */

#define __HI(x) *(1+(int*)&x)
#define __LO(x) *(int*)&x

static const double
bp[] = {1.0, 1.5,},
dp_h[] = { 0.0, 5.84962487220764160156e-01,}, /* 0x3FE2B803, 0x40000000 */
dp_l[] = { 0.0, 1.35003920212974897128e-08,}, /* 0x3E4CFDEB, 0x43CFD006 */
zero    =  0.0,
one    =  1.0,
two    =  2.0,
two53    =  9007199254740992.0,    /* 0x43400000, 0x00000000 */
huge    =  1.0e300,
tiny    =  1.0e-300,
        /* for scalbn */
two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
    /* poly coefs for (3/2)*(log(x)-2s-2/3*s**3 */
L1  =  5.99999999999994648725e-01, /* 0x3FE33333, 0x33333303 */
L2  =  4.28571428578550184252e-01, /* 0x3FDB6DB6, 0xDB6FABFF */
L3  =  3.33333329818377432918e-01, /* 0x3FD55555, 0x518F264D */
L4  =  2.72728123808534006489e-01, /* 0x3FD17460, 0xA91D4101 */
L5  =  2.30660745775561754067e-01, /* 0x3FCD864A, 0x93C9DB65 */
L6  =  2.06975017800338417784e-01, /* 0x3FCA7E28, 0x4A454EEF */
P1   =  1.66666666666666019037e-01, /* 0x3FC55555, 0x5555553E */
P2   = -2.77777777770155933842e-03, /* 0xBF66C16C, 0x16BEBD93 */
P3   =  6.61375632143793436117e-05, /* 0x3F11566A, 0xAF25DE2C */
P4   = -1.65339022054652515390e-06, /* 0xBEBBBD41, 0xC5D26BF1 */
P5   =  4.13813679705723846039e-08, /* 0x3E663769, 0x72BEA4D0 */
lg2  =  6.93147180559945286227e-01, /* 0x3FE62E42, 0xFEFA39EF */
lg2_h  =  6.93147182464599609375e-01, /* 0x3FE62E43, 0x00000000 */
lg2_l  = -1.90465429995776804525e-09, /* 0xBE205C61, 0x0CA86C39 */
ovt =  8.0085662595372944372e-0017, /* -(1024-log2(ovfl+.5ulp)) */
cp    =  9.61796693925975554329e-01, /* 0x3FEEC709, 0xDC3A03FD =2/(3ln2) */
cp_h  =  9.61796700954437255859e-01, /* 0x3FEEC709, 0xE0000000 =(float)cp */
cp_l  = -7.02846165095275826516e-09, /* 0xBE3E2FE0, 0x145B01F5 =tail of cp_h*/
ivln2    =  1.44269504088896338700e+00, /* 0x3FF71547, 0x652B82FE =1/ln2 */
ivln2_h  =  1.44269502162933349609e+00, /* 0x3FF71547, 0x60000000 =24b 1/ln2*/
ivln2_l  =  1.92596299112661746887e-08; /* 0x3E54AE0B, 0xF85DDF44 =1/ln2 tail*/

inline double fdlibmScalbn (double x, int n)
{
    int  k,hx,lx;
    hx = __HI(x);
    lx = __LO(x);
        k = (hx&0x7ff00000)>>20;        /* extract exponent */
        if (k==0) {                /* 0 or subnormal x */
            if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
        x *= two54; 
        hx = __HI(x);
        k = ((hx&0x7ff00000)>>20) - 54; 
            if (n< -50000) return tiny*x;     /*underflow*/
        }
        if (k==0x7ff) return x+x;        /* NaN or Inf */
        k = k+n; 
        if (k >  0x7fe) return huge*copysign(huge,x); /* overflow  */
        if (k > 0)                 /* normal result */
        {__HI(x) = (hx&0x800fffff)|(k<<20); return x;}
        if (k <= -54) {
            if (n > 50000)     /* in case integer overflow in n+k */
        return huge*copysign(huge,x);    /*overflow*/
        else return tiny*copysign(tiny,x);     /*underflow*/
        }
        k += 54;                /* subnormal result */
        __HI(x) = (hx&0x800fffff)|(k<<20);
        return x*twom54;
}

double fdlibmPow(double x, double y)
{
    double z,ax,z_h,z_l,p_h,p_l;
    double y1,t1,t2,r,s,t,u,v,w;
    int i0,i1,i,j,k,yisint,n;
    int hx,hy,ix,iy;
    unsigned lx,ly;

    i0 = ((*(int*)&one)>>29)^1; i1=1-i0;
    hx = __HI(x); lx = __LO(x);
    hy = __HI(y); ly = __LO(y);
    ix = hx&0x7fffffff;  iy = hy&0x7fffffff;

    /* y==zero: x**0 = 1 */
    if((iy|ly)==0) return one;     

    /* +-NaN return x+y */
    if(ix > 0x7ff00000 || ((ix==0x7ff00000)&&(lx!=0)) ||
       iy > 0x7ff00000 || ((iy==0x7ff00000)&&(ly!=0))) 
        return x+y;    

    /* determine if y is an odd int when x < 0
     * yisint = 0    ... y is not an integer
     * yisint = 1    ... y is an odd int
     * yisint = 2    ... y is an even int
     */
    yisint  = 0;
    if(hx<0) {    
        if(iy>=0x43400000) yisint = 2; /* even integer y */
        else if(iy>=0x3ff00000) {
        k = (iy>>20)-0x3ff;       /* exponent */
        if(k>20) {
            j = ly>>(52-k);
            if(static_cast<unsigned>(j<<(52-k))==ly) yisint = 2-(j&1);
        } else if(ly==0) {
            j = iy>>(20-k);
            if((j<<(20-k))==iy) yisint = 2-(j&1);
        }
        }        
    } 

    /* special value of y */
    if(ly==0) {     
        if (iy==0x7ff00000) {    /* y is +-inf */
            if(((ix-0x3ff00000)|lx)==0)
            return  y - y;    /* inf**+-1 is NaN */
            else if (ix >= 0x3ff00000)/* (|x|>1)**+-inf = inf,0 */
            return (hy>=0)? y: zero;
            else            /* (|x|<1)**-,+inf = inf,0 */
            return (hy<0)?-y: zero;
        } 
        if(iy==0x3ff00000) {    /* y is  +-1 */
        if(hy<0) return one/x; else return x;
        }
        if(hy==0x40000000) return x*x; /* y is  2 */
        if(hy==0x3fe00000) {    /* y is  0.5 */
        if(hx>=0)    /* x >= +0 */
        return sqrt(x);    
        }
    }

    ax   = fabs(x);
    /* special value of x */
    if(lx==0) {
        if(ix==0x7ff00000||ix==0||ix==0x3ff00000){
        z = ax;            /*x is +-0,+-inf,+-1*/
        if(hy<0) z = one/z;    /* z = (1/|x|) */
        if(hx<0) {
            if(((ix-0x3ff00000)|yisint)==0) {
            z = (z-z)/(z-z); /* (-1)**non-int is NaN */
            } else if(yisint==1) 
            z = -z;        /* (x<0)**odd = -(|x|**odd) */
        }
        return z;
        }
    }
    
    n = (hx>>31)+1;

    /* (x<0)**(non-int) is NaN */
    if((n|yisint)==0) return (x-x)/(x-x);

    s = one; /* s (sign of result -ve**odd) = -1 else = 1 */
    if((n|(yisint-1))==0) s = -one;/* (-ve)**(odd int) */

    /* |y| is huge */
    if(iy>0x41e00000) { /* if |y| > 2**31 */
        if(iy>0x43f00000){    /* if |y| > 2**64, must o/uflow */
        if(ix<=0x3fefffff) return (hy<0)? huge*huge:tiny*tiny;
        if(ix>=0x3ff00000) return (hy>0)? huge*huge:tiny*tiny;
        }
    /* over/underflow if x is not close to one */
        if(ix<0x3fefffff) return (hy<0)? s*huge*huge:s*tiny*tiny;
        if(ix>0x3ff00000) return (hy>0)? s*huge*huge:s*tiny*tiny;
    /* now |1-x| is tiny <= 2**-20, suffice to compute 
       log(x) by x-x^2/2+x^3/3-x^4/4 */
        t = ax-one;        /* t has 20 trailing zeros */
        w = (t*t)*(0.5-t*(0.3333333333333333333333-t*0.25));
        u = ivln2_h*t;    /* ivln2_h has 21 sig. bits */
        v = t*ivln2_l-w*ivln2;
        t1 = u+v;
        __LO(t1) = 0;
        t2 = v-(t1-u);
    } else {
        double ss,s2,s_h,s_l,t_h,t_l;
        n = 0;
    /* take care subnormal number */
        if(ix<0x00100000)
        {ax *= two53; n -= 53; ix = __HI(ax); }
        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;}
        __HI(ax) = ix;

    /* compute ss = s_h+s_l = (x-1)/(x+1) or (x-1.5)/(x+1.5) */
        u = ax-bp[k];        /* bp[0]=1.0, bp[1]=1.5 */
        v = one/(ax+bp[k]);
        ss = u*v;
        s_h = ss;
        __LO(s_h) = 0;
    /* t_h=ax+bp[k] High */
        t_h = zero;
        __HI(t_h)=((ix>>1)|0x20000000)+0x00080000+(k<<18); 
        t_l = ax - (t_h-bp[k]);
        s_l = v*((u-s_h*t_h)-s_h*t_l);
    /* compute log(ax) */
        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;
        __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;
    /* 2/(3log2)*(ss+...) */
        p_h = u+v;
        __LO(p_h) = 0;
        p_l = v-(p_h-u);
        z_h = cp_h*p_h;        /* cp_h+cp_l = 2/(3*log2) */
        z_l = cp_l*p_h+p_l*cp+dp_l[k];
    /* log2(ax) = (ss+..)*2/(3*log2) = n + dp_h + z_h + z_l */
        t = (double)n;
        t1 = (((z_h+z_l)+dp_h[k])+t);
        __LO(t1) = 0;
        t2 = z_l-(((t1-t)-dp_h[k])-z_h);
    }

    /* split up y into y1+y2 and compute (y1+y2)*(t1+t2) */
    y1  = y;
    __LO(y1) = 0;
    p_l = (y-y1)*t1+y*t2;
    p_h = y1*t1;
    z = p_l+p_h;
    j = __HI(z);
    i = __LO(z);
    if (j>=0x40900000) {                /* z >= 1024 */
        if(((j-0x40900000)|i)!=0)            /* if z > 1024 */
        return s*huge*huge;            /* overflow */
        else {
        if(p_l+ovt>z-p_h) return s*huge*huge;    /* overflow */
        }
    } else if((j&0x7fffffff)>=0x4090cc00 ) {    /* z <= -1075 */
        if(((j-0xc090cc00)|i)!=0)         /* z < -1075 */
        return s*tiny*tiny;        /* underflow */
        else {
        if(p_l<=z-p_h) return s*tiny*tiny;    /* underflow */
        }
    }
    /*
     * compute 2**(p_h+p_l)
     */
    i = j&0x7fffffff;
    k = (i>>20)-0x3ff;
    n = 0;
    if(i>0x3fe00000) {        /* if |z| > 0.5, set n = [z+0.5] */
        n = j+(0x00100000>>(k+1));
        k = ((n&0x7fffffff)>>20)-0x3ff;    /* new k for n */
        t = zero;
        __HI(t) = (n&~(0x000fffff>>k));
        n = ((n&0x000fffff)|0x00100000)>>(20-k);
        if(j<0) n = -n;
        p_h -= t;
    } 
    t = p_l+p_h;
    __LO(t) = 0;
    u = t*lg2_h;
    v = (p_l-(t-p_h))*lg2+t*lg2_l;
    z = u+v;
    w = v-(z-u);
    t  = z*z;
    t1  = z - t*(P1+t*(P2+t*(P3+t*(P4+t*P5))));
    r  = (z*t1)/(t1-two)-(w+z*w);
    z  = one-(r-z);
    j  = __HI(z);
    j += (n<<20);
    if((j>>20)<=0) z = fdlibmScalbn(z,n);    /* subnormal output */
    else __HI(z) += (n<<20);
    return s*z;
}

#endif

} // namespace JSC