Decoding:
    SILC_ASN1_CHOICE

    Macro used to specify choices in decoding.  The choice list must
    be terminated with SILC_ASN1_END.  There is no limit how many choices
    can be specified in the list.

    // Decode timeval that is either UTC or generalized time
    silc_asn1_decode(asn1, tree,
                     SILC_ASN1_SEQUENCE,
                       SILC_ASN1_CHOICE,
                         SILC_ASN1_UTC_TIME(&timeval),
                         SILC_ASN1_GEN_TIME(&timeval),
                       SILC_ASN1_END,
                     SILC_ASN1_END, SILC_ASN1_END);