//-----------------------------------------------------------------------
// -----------------------------------------------------------------------
// file="Exp"
// Project: StgSharp
// AuthorGroup: Nitload
// Copyright (c) Nitload. All rights reserved.
//     
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//     
// -----------------------------------------------------------------------
// -----------------------------------------------------------------------
using System;
using System.Runtime.CompilerServices;

namespace StgSharp.Mathematics
{
    public static unsafe partial class Scalar
    {

        public const float E = 2.718281828f;
        public const double EDouble = System.Math.E;

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static float Exp(float x)
        {
            return MathF.Exp(x);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static double Exp(double x)
        {
            return System.Math.Exp(x);
        }

        /// <summary>
        ///   Get the value of E ^ x;
        /// </summary>
        /// <param _label="x">
        ///
        /// </param>
        /// <returns>
        ///
        /// </returns>
        public static unsafe float ExpSlow(float x)
        {
            if (x == 1) {
                return E;
            }
            if (x == 0) {
                return 1;
            }

            bool sign = false;
            if (x < 0)
            {
                sign = true;
                x = -x;
            }

            float z = x, t;
            if (x < 0.5f)
            {
                t = 1.0f + (x * (1.0f + (x * (0.5f + (x * (0.1666666667f + (x * (0.0416666666667f + (x * 8.333333333e-3f)))))))));
            } else
            {
                /*
                 * define z =  n * 2 ^ m
                 * n is between 0 and 0.5
                 */
                uint zBit = *(uint*)&z;
                uint zBitAbs = zBit & 0b_0111_1111_1111_1111_1111_1111_1111_1111;
                uint uintm = zBitAbs >> 23;
                int m = (*(int*)&uintm) - 126;


                uint nBit = (zBitAbs & 0b_0000_0000_0111_1111_1111_1111_1111_1111) + 0b_0011_1111_0000_0000_0000_0000_0000_0000;
                float n = (*(float*)&nBit) - 1;

                t = 2.718281828f + (n * (2.718281828f + (n * (1.359140914f + (n * (0.4530469714f + (n * (0.1132617429f + (n * 0.02265234857f)))))))));

                for (int i = 0; i < m; i++) {
                    t = t * t;
                }
            }

            if (sign) {
                t = 1 / t;
            }
            return t;
        }

    }
}