// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Runtime.Intrinsics;

namespace System.Numerics.Tensors
{
    public static partial class TensorPrimitives
    {
        /// <summary>Computes the element-wise result of raising <c>e</c> to the number powers in the specified tensor, minus 1.</summary>
        /// <param name="x">The tensor, represented as a span.</param>
        /// <param name="destination">The destination tensor, represented as a span.</param>
        /// <exception cref="ArgumentException">Destination is too short.</exception>
        /// <exception cref="ArgumentException"><paramref name="x"/> and <paramref name="destination"/> reference overlapping memory locations and do not begin at the same location.</exception>
        /// <remarks>
        /// <para>
        /// This method effectively computes <c><paramref name="destination" />[i] = <typeparamref name="T"/>.ExpM1(<paramref name="x" />[i])</c>.
        /// </para>
        /// <para>
        /// This method may call into the underlying C runtime or employ instructions specific to the current architecture. Exact results may differ between different
        /// operating systems or architectures.
        /// </para>
        /// </remarks>
        public static void ExpM1<T>(ReadOnlySpan<T> x, Span<T> destination)
            where T : IExponentialFunctions<T>
        {
            if (typeof(T) == typeof(Half) && TryUnaryInvokeHalfAsInt16<T, ExpM1Operator<float>>(x, destination))
            {
                return;
            }

            InvokeSpanIntoSpan<T, ExpM1Operator<T>>(x, destination);
        }

        /// <summary>T.ExpM1(x)</summary>
        private readonly struct ExpM1Operator<T> : IUnaryOperator<T, T>
            where T : IExponentialFunctions<T>
        {
            public static bool Vectorizable => ExpOperator<T>.Vectorizable;

            public static T Invoke(T x) => T.ExpM1(x);
            public static Vector128<T> Invoke(Vector128<T> x) => ExpOperator<T>.Invoke(x) - Vector128<T>.One;
            public static Vector256<T> Invoke(Vector256<T> x) => ExpOperator<T>.Invoke(x) - Vector256<T>.One;
            public static Vector512<T> Invoke(Vector512<T> x) => ExpOperator<T>.Invoke(x) - Vector512<T>.One;
        }
    }
}