UVtools/UVtools.Core/Extensions/SpanExtensions.cs

using System;
using System.Runtime.CompilerServices;
using System.Threading.Tasks;

namespace UVtools.Core.Extensions
{
    public static class SpanExtensions
    {
        public static unsafe void Fill<T>(this Span<T> span, Func<T> provider) where T : struct
        {
            int
                cores = Environment.ProcessorCount,
                batch = span.Length / cores,
                mod = span.Length % cores,
                size = Unsafe.SizeOf<T>();
            ref T r0 = ref span.GetPinnableReference();
            fixed (byte* p0 = &Unsafe.As<T, byte>(ref r0))
            {
                byte* p = p0;
                Parallel.For(0, cores, i =>
                {
                    byte* pi = p + i * batch * size;
                    for (int j = 0; j < batch; j++, pi += size)
                        Unsafe.Write(pi, provider());
                });

                // Remaining values
                if (mod < 1) return;
                for (int i = span.Length - mod; i < span.Length; i++)
                    Unsafe.Write(p + i * size, provider());
            }
        }
    }
}