Convert function from c# to swift

I need this function converted from c# to swift.

public static string UnzipString(string compressedText)
{
byte[] array = Convert.FromBase64String(compressedText);
using MemoryStream memoryStream = new MemoryStream();
int num = BitConverter.ToInt32(array, 0);
memoryStream.Write(array, 4, array.Length - 4);
byte[] array2 = new byte[num];
memoryStream.Position = 0L;
using (GZipStream gZipStream = new GZipStream(memoryStream, CompressionMode.Decompress))
{
gZipStream.Read(array2, 0, array2.Length);
}
return Encoding.UTF8.GetString(array2);
}

Here are some example compressed strings.

<string>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</string>
<string>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</string>
<string>pQMAAB+LCAAAAAAABAC9U1tPwjAUfjfxPyzz2bW7sA5TagxINBlqgOh8nFBHzWhJd3Dw7y1VYPKAxge3ZNl36flOtx56uZqXzjvXlVCy4/oedh0uJ2oqZNFxl/B67sfuJTs9ob2s39N5Le9f3vgEHLNMVheratpxZwCLC4Tquvbq0FO6QAHGPsoG6Wgy4/Pc3ZnFz+ZzISvI5YS7JtRx6IMSEqpUVGCxYR5NvNLBFzRExoK4FZMQ+14Y4oiYO6Ao2xueWZJEXtJqRyTx22Gc+Amh6HlbEH2veCQg8EwFEicEx/8fEHsYE0ICvxWbiCj8U8CxT/TbAIoOfgrtcglcW3a7ImN4H2DK4201ig7d9FqCgPV4veAsFcUMnvjm+aDKdSkkp6ihW/9t1S1VxacM9NLIO/jZiyqVHoE2B5idYdw3l4lskNZ1VYpCzk0jbKwWKX8FivaUdfSVhBFsOijYkBfLMtcUNUnrGirIwYzOZn+7d6uM+Qpu7EY2WgNZNc3XXN/lc84G12lE0R6bUUPfZ419ABCZzLWlAwAA</string>