[python-win32] ATT DSP32C to IEEE

[Ray Schumacher]

Following myself, I just made two new methods using array and struct, if anyone's interested:


def _DSP32ToIEEE(fh, address):
    """  bytes == 4 
    to convert from DSP32C binary files
    smmmmmmm mmmmmmmm mmmmmmmm eeeeeeee
    to IEEE float
    seeeeeee emmmmmmm mmmmmmmm mmmmmmmm
    """

    fh.seek(address)
    dat = struct.unpack('L', fh.read(4))[0]
    
    s = dat>>31
    m = (dat & 0x7fffffff)>>8
    e = (dat & 0x000000ff)
    #print s, m, e
    
    arrf = array.array('f')
    if s==0:
        arrL[0] = (e<<23) + m ## a long
        arrf.fromstring(arrL.tostring())
        arrf[0] = arrf[0]/2.
    else:
        arrL[0] = (s<<31) + (e<<23) + ~m ## a long, mantissa complemented
        arrf.fromstring(arrL.tostring())
    fh.seek(address)
    return arrf[0]

-OR-

arrf = array.array('f')
then...
IEEEValue = DSP32ToIEEE(arrf, struct.unpack('L', fh.read(4))[0])

def DSP32ToIEEE(arrf, longVal):
    """  arrf is an array() instance
    len(longVal) == 4 
    to convert from DSP32C binary value
    smmmmmmm mmmmmmmm mmmmmmmm eeeeeeee
    to IEEE float
    seeeeeee emmmmmmm mmmmmmmm mmmmmmmm
    """
    if not longVal>>31:
        arrL[0] = ((longVal & 0x000000ff)<<23) + \
            ((longVal & 0x7fffffff)>>8) ## a long
        arrf.fromstring(arrL.tostring())
        arrf[0] = arrf[0]/2.
    else:
        arrL[0] = (1<<31) + ((longVal & 0x000000ff)<<23) + \
            ~((longVal & 0x7fffffff)>>8) ## a long, mantissa complemented
        arrf.fromstring(arrL.tostring())
    
    return arrf.pop() ## remove the only item



May want some re-factoring, but is now much faster...

Ray



















At 08:00 AM 1/6/2006, Thomas Heller wrote:

>RayS <rays at blue-cove.com> writes:
>
>> I'm trying to find an efficient way to convert from DSP32C binary files
>> smmmmmmm mmmmmmmm mmmmmmmm eeeeeeee
>> to IEEE float
>> seeeeeee emmmmmmm mmmmmmmm mmmmmmmm
>>
>> I tried struct and bit-shifting from a C manual example, but it 
>> failed. Has someone else coded this in Python? I'll post the early 
>> attempt when I get into the office later, if not.
>>
>> I re-coded from scratch, converting each 32 bit ATT value to a binary 
>> string, slice-rearranging bits, then re-packing to IEEE. A bit 
>> slowwwww. At least they're small files.
>
>You could try ctypes bitfield structures, maybe, to access the fields?
>
>Thomas
>
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