//-----------------------------------------------------------------------
// -----------------------------------------------------------------------
// file="Exp.cs"
// Project: StgSharp
// AuthorGroup: Nitload Space
// Copyright (c) Nitload Space. 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 Scaler
    {

        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;
        }

    }
}