Function _get_machar

numpy/core/getlimits.py:307–361

Get MachAr instance or MachAr-like instance Get parameters for floating point type, by first trying signatures of various known floating point types, then, if none match, attempting to identify parameters by analysis. Parameters ---------- ftype : class Numpy float

(ftype)

def _get_machar(ftype):
    """ Get MachAr instance or MachAr-like instance

    Get parameters for floating point type, by first trying signatures of
    various known floating point types, then, if none match, attempting to
    identify parameters by analysis.

    Parameters
    ----------
    ftype : class
        Numpy floating point type class (e.g. ``np.float64``)

    Returns
    -------
    ma_like : instance of :class:`MachAr` or :class:`MachArLike`
        Object giving floating point parameters for `ftype`.

    Warns
    -----
    UserWarning
        If the binary signature of the float type is not in the dictionary of
        known float types.
    """
    params = _MACHAR_PARAMS.get(ftype)
    if params is None:
        raise ValueError(repr(ftype))
    # Detect known / suspected types
    # ftype(-1.0) / ftype(10.0) is better than ftype('-0.1') because stold
    # may be deficient
    key = (ftype(-1.0) / ftype(10.)).newbyteorder('<').tobytes()
    ma_like = None
    if ftype == ntypes.longdouble:
        # Could be 80 bit == 10 byte extended precision, where last bytes can
        # be random garbage.
        # Comparing first 10 bytes to pattern first to avoid branching on the
        # random garbage.
        ma_like = _KNOWN_TYPES.get(key[:10])
    if ma_like is None:
        # see if the full key is known.
        ma_like = _KNOWN_TYPES.get(key)
    if ma_like is None and len(key) == 16:
        # machine limits could be f80 masquerading as np.float128,
        # find all keys with length 16 and make new dict, but make the keys
        # only 10 bytes long, the last bytes can be random garbage
        _kt = {k[:10]: v for k, v in _KNOWN_TYPES.items() if len(k) == 16}
        ma_like = _kt.get(key[:10])
    if ma_like is not None:
        return ma_like
    # Fall back to parameter discovery
    warnings.warn(
        f'Signature {key} for {ftype} does not match any known type: '
        'falling back to type probe function.\n'
        'This warnings indicates broken support for the dtype!',
        UserWarning, stacklevel=2)
    return _discovered_machar(ftype)


def _discovered_machar(ftype):