Source code for irfpy.ica.floats

"""Handling of minifloats (f8) as used by ICA

.. codeauthor:: Martin Wieser

Module: irfpy.ica.floats

Functions to convert between f8 minifloats and integers.
ICA minifloats are 8 bit in size and have the following structure:

s: sign bits
e: exponent bits
m: mantissa bits

s.e.m   excess  integer range covered
0.4.4   -4(?)   0 to 507904

.. autosummary::


"""

import logging
logging.basicConfig()
_logger = logging.getLogger('ica.floats')
_logger.setLevel(logging.DEBUG)


def u24_f8(u24):
    """ Convert an 24 bit integer to a f8 minifloat.
    In case of overflow 0xFF is returned
    """
    if u24 > 507904:
        return 0xFF
    elif u24 < 0x10:
        return u24
    else:
        e = 1
        m = u24
        while m >= 0x20:
            m = m >> 1
            e = e + 1
        # x is now 0x10 .. 0x1F
        m = m & 0xF  # mask away 0x10
        return (e << 4) + m


def f8_u16(f8):
    """ Convert a f8 minifloat to 16-bit integer. In case of overflow 0xFFFF is returned
    """
    e = f8 & 0xF0
    if e < 0x10:
        return f8
    e = (e >> 4) - 1
    if e > 11:
        return 0xFFFF
    return ((f8 & 0xF) | 0x10) << e


def f8_u24(f8):
    """ Convert a f8 minifloat to 24-bit integer. no overflow possible
    """
    e = f8 & 0xF0
    if e < 0x10:
        return f8
    e = (e >> 4) - 1
    return ((f8 & 0xF) | 0x10) << e