class SVP64RMFields(SelectableIntMapping, bits=24, fields={
            "spr": range(24),
            # SVP64 RM fields: see https://libre-soc.org/openpower/sv/svp64/
            "mmode": (0,),
            "mask": range(1, 4),
            "elwidth": range(4, 6),
            "ewsrc": range(6, 8),
            "subvl": range(8, 10),
            "extra": range(10, 19),
            "mode": range(19, 24),
            # these cover the same extra field, split into parts as EXTRA2
            "extra2": dict(enumerate([
                range(10, 12),
                range(12, 14),
                range(14, 16),
                range(16, 18),
            ])),
            "smask": range(16, 19),
            # and here as well, but EXTRA3
            "extra3": dict(enumerate([
                range(10, 13),
                range(13, 16),
                range(16, 19),
            ])),
        }):

    def __init__(self, value=0):
        super().__init__(value=value)
        self.spr = self


SVP64RM_MMODE_SIZE = len(SVP64RMFields.mmode)
SVP64RM_MASK_SIZE = len(SVP64RMFields.mask)
SVP64RM_ELWIDTH_SIZE = len(SVP64RMFields.elwidth)
SVP64RM_EWSRC_SIZE = len(SVP64RMFields.ewsrc)
SVP64RM_SUBVL_SIZE = len(SVP64RMFields.subvl)
SVP64RM_EXTRA2_SPEC_SIZE = len(SVP64RMFields.extra2[0])
SVP64RM_EXTRA3_SPEC_SIZE = len(SVP64RMFields.extra3[0])
SVP64RM_SMASK_SIZE = len(SVP64RMFields.smask)
SVP64RM_MODE_SIZE = len(SVP64RMFields.mode)