System.Runtime.InteropServices.DllImportAttribute.GetCustomAttribute C# (CSharp) Method

        internal static Attribute GetCustomAttribute(RuntimeMethodInfo method) 
        { 
            if ((method.Attributes & MethodAttributes.PinvokeImpl) == 0)
                return null;

            MetadataImport scope = method.Module.ModuleHandle.GetMetadataImport();
            string entryPoint, dllName = null;
            int token = method.MetadataToken;
            PInvokeAttributes flags = 0;
            
            scope.GetPInvokeMap(token, out flags, out entryPoint, out dllName);

            CharSet charSet = CharSet.None;

            switch (flags & PInvokeAttributes.CharSetMask)
            {
                case PInvokeAttributes.CharSetNotSpec: charSet = CharSet.None; break;
                case PInvokeAttributes.CharSetAnsi: charSet = CharSet.Ansi; break;
                case PInvokeAttributes.CharSetUnicode: charSet = CharSet.Unicode; break;
                case PInvokeAttributes.CharSetAuto: charSet = CharSet.Auto; break;
                default: ASSERT.UNREACHABLE(); break;
            }

            CallingConvention callingConvention = CallingConvention.Cdecl;

            switch (flags & PInvokeAttributes.CallConvMask)
            {
                case PInvokeAttributes.CallConvWinapi :callingConvention = CallingConvention.Winapi; break;
                case PInvokeAttributes.CallConvCdecl :callingConvention = CallingConvention.Cdecl; break;
                case PInvokeAttributes.CallConvStdcall :callingConvention = CallingConvention.StdCall; break;
                case PInvokeAttributes.CallConvThiscall :callingConvention = CallingConvention.ThisCall; break;
                case PInvokeAttributes.CallConvFastcall :callingConvention = CallingConvention.FastCall; break;

                default: ASSERT.UNREACHABLE(); break;
            }

            bool exactSpelling = (flags & PInvokeAttributes.NoMangle) != 0;
            bool setLastError = (flags & PInvokeAttributes.SupportsLastError) != 0;
            bool bestFitMapping = (flags & PInvokeAttributes.BestFitMask) == PInvokeAttributes.BestFitEnabled;
            bool throwOnUnmappableChar = (flags & PInvokeAttributes.ThrowOnUnmappableCharMask) == PInvokeAttributes.ThrowOnUnmappableCharEnabled;
            bool preserveSig = (method.GetMethodImplementationFlags() & MethodImplAttributes.PreserveSig) != 0;

            return new DllImportAttribute(
                dllName, entryPoint, charSet, exactSpelling, setLastError, preserveSig,
                callingConvention, bestFitMapping, throwOnUnmappableChar);
        }