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Code: Alles auswählen

    for i in xrange(0x100):
        fp = BASIC09FloatingPoint(i)
        print "%3s -> %s" % (
            i,
            " ".join(["$%02x" % i for i in fp.get_bytes()])
        )

Code: Alles auswählen

from __future__ import print_function
import math
from struct import Struct

MFLOAT_STRUCT = Struct('>BI')
FAC_FLOAT_STRUCT = Struct('>BIb')
assert MFLOAT_STRUCT.size == 5 and FAC_FLOAT_STRUCT.size == 6


def _float2cbm_float(value):
    sign = 0
    mantissa, exponent = math.frexp(value)
    
    if mantissa or exponent:
        exponent += 128
        if not 0 <= exponent <= 255:
            raise OverflowError

        if mantissa < 0:
            mantissa = -mantissa
            sign = 1

        mantissa = mantissa * 2**32

    return exponent, int(mantissa + 0.5), sign


def float2cbm_mfloat(value):
    exponent, mantissa, sign = _float2cbm_float(value)
    return MFLOAT_STRUCT.pack(exponent, (mantissa & 0x7fffffff) | (sign << 31))


def float2cbm_fac_float(value):
    exponent, mantissa, sign = _float2cbm_float(value)
    return FAC_FLOAT_STRUCT.pack(exponent, mantissa, -1 if sign else 0)


def cbm_float2float(value):
    if len(value) == 5:
        exponent, mantissa = MFLOAT_STRUCT.unpack(value)
        sign = mantissa >> 31
        if exponent:
            mantissa |= 0x80000000
    elif len(value) == 6:
        exponent, mantissa, sign = FAC_FLOAT_STRUCT.unpack(value)
    else:
        raise ValueError('wrong byte length for a cbm float')

    result = mantissa * 2.0**(exponent - 128 - 32)
    return -result if sign else result


def main():
    for value in [
        0, 0.5, 0.1, -1, -0.25, 100, -1000, -42.23, 3.141592653589793, 10e200
    ]:
        mfloat = float2cbm_mfloat(value)
        fac_float = float2cbm_fac_float(value)
        py_float_a = cbm_float2float(mfloat)
        py_float_b = cbm_float2float(fac_float)
        print(
            mfloat.encode('hex'),
            fac_float.encode('hex'),
            value,
            py_float_a,
            py_float_a == py_float_b,
            value - py_float_a
        )


if __name__ == '__main__':
    main()