msbin to ieee

[revuesbio]

On 7 mai, 23:38, John Machin <sjmac... at lexicon.net> wrote:
> On May 7, 11:37 pm, revuesbio <revues... at gmail.com> wrote:
>
>
>
> > On 7 mai, 14:56, John Machin <sjmac... at lexicon.net> wrote:
>
> > > On May 7, 10:00 pm, revuesbio <revues... at gmail.com> wrote:
>
> > > > On 7 mai, 13:21, John Machin <sjmac... at lexicon.net> wrote:
>
> > > > > On May 7, 6:18 pm, revuesbio <revues... at gmail.com> wrote:
>
> > > > > > On 7 mai, 03:52, John Machin <sjmac... at lexicon.net> wrote:
>
> > > > > > > On May 7, 7:44 am, revuesbio <revues... at gmail.com> wrote:
>
> > > > > > > > Hi
> > > > > > > > Does anyone have the python version of the conversion from msbin to
> > > > > > > > ieee?
> > > > > > > > Thank u
>
> > > > > > > Yes, Google has it. Google is your friend. Ask Google. It will lead
> > > > > > > you to such as:
>
> > > > > > >http://mail.python.org/pipermail/python-list/2005-August/337817.html
>
> > > > > > > HTH,
> > > > > > > John
>
> > > > > > Thank you,
>
> > > > > > I've already read it but the problem is always present. this script is
> > > > > > for double precision MBF format ( 8 bytes).
>
> > > > > It would have been somewhat more helpful had you said what you had
> > > > > done so far,  even posted your code ...
>
> > > > > > I try to adapt this script for single precision MBF format ( 4 bytes)
> > > > > > but i don't find the right float value.
>
> > > > > > for example : 'P\xad\x02\x95' will return '0.00024924660101532936'
>
> > > > > If you know what the *correct* value is, you might like to consider
> > > > > shifting left by log2(correct_value/erroneous_value) :-)
>
> > > > > Do you have any known correct pairs of (mbf4 string, decimal_float
> > > > > value)? My attempt is below -- this is based on a couple of
> > > > > descriptive sources that my friend Google found, with no test data. I
> > > > > believe the correct answer for the above input is 1070506.0 i.e. you
> > > > > are out by a factor of 2 ** 32
>
> > > > > def mbf4_as_float(s):
> > > > >     m0, m1, m2, m3 = [ord(c) for c in s]
> > > > >     exponent = m3
> > > > >     if not exponent:
> > > > >         return 0.0
> > > > >     sign = m2 & 0x80
> > > > >     m2 |= 0x80
> > > > >     mant = (((m2 << 8) | m1) << 8) | m0
> > > > >     adj = 24 + 128
> > > > >     num = mant * 2.0 ** (exponent - adj)
> > > > >     if sign:
> > > > >         return -num
> > > > >     return num
>
> > > > > HTH,
> > > > > John
>
> > > > well done ! it's exactly what i'm waiting for !!
>
> > > > my code was:>>> from struct import *
> > > > >>> x = list(unpack('BBBB','P\xad\x02\x95'))
> > > > >>> x
> > > > [80, 173, 2, 149]
> > > > >>> def conversion1(bytes):
>
> > > > b=bytes[:]
> > > > sign = bytes[-2] & 0x80
> > > > b[-2] |= 0x80
> > > > exp = bytes[-1] - 0x80 - 56
> > > > acc = 0L
> > > > for i,byte in enumerate(b[:-1]):
> > > > acc |= (long(byte)<<(i*8))
> > > > return (float(acc)*2.0**exp)*((1.,-1.)[sign!=0])
>
> > > Apart from the 2**32 problem, the above doesn't handle *any* of the
> > > 2**24 different representations of zero. Try feeding \0\0\0\0' to it
> > > and see what you get.
>
> > > > >>> conversion1(x)
>
> > > > 0.00024924660101532936
>
> > > > this script come from google groups but i don't understand bit-string
> > > > manipulation (I'm a  newbie). informations about bit-string
> > > > manipulation with python is too poor on the net.
>
> > > The basic operations (and, or, exclusive-or, shift) are not specific
> > > to any language. Several  languages share the same notation (& | ^ <<
>
> > > >>), having inherited it from C.
>
> > > > thank you very much for your script.
>
> > > Don't thank me, publish some known correct pairs of values so that we
> > > can verify that it's not just accidentally correct for 1 pair of
> > > values.
>
> > pairs of values :
> > (bytes string, mbf4_as_float(s) result)                        right
> > float value
> > ('P\xad\x02\x95', 1070506.0)
> > 1070506.0
> > ('\x00\x00\x00\x02', 5.8774717541114375e-039)         0.0
>
> There is no way that \x00\x00\x00\x02' could represent exactly zero.
> What makes you think it does? Rounding?
>
> > ('\x00\x00\x00\x81', 1.0)
> > 1.0
> > ('\x00\x00\x00\x82', 2.0)
> > 2.0
> > ('\x00\x00@\x82', 3.0)
> > 3.0
> > ('\x00\x00\x00\x83', 4.0)
> > 4.0
> > ('\x00\x00 \x83', 5.0)
> > 5.0
> > ('\xcd\xcc\x0c\x81', 1.1000000238418579)                 1.1
> > ('\xcd\xcc\x0c\x82', 2.2000000476837158)                  2.2
> > ('33S\x82', 3.2999999523162842)                              3.3
> > ('\xcd\xcc\x0c\x83', 4.4000000953674316)                  4.4
>
> It is not apparent whether you regard the output from the function as
> correct or not.
>
> 4.4 "converted" to mbf4 format is '\xcd\xcc\x0c\x83' which is
> 4.4000000953674316 which is the closest possible mbf4 representation
> of 4.4 (difference is 9.5e-008).
>
> The next lower mbf4 value '\xcc\xcc\x0c\x83' is 4.3999996185302734
> (difference is   -3.8e-007).
>
> Note that floating-point representation of many decimal fractions is
> inherently inexact. print repr(4.4) produces 4.4000000000000004
>
> Have you read this:
>    http://docs.python.org/tut/node16.html
> ?
>
> If you need decimal-fraction output that matches what somebody typed
> into the original software, or saw on the screen, you will need to
> know/guess the precision that was involved, and round the numbers
> accordingly -- just like the author of the original software would
> have needed to do.
>
> >>> ['%.*f' % (decplaces, 4.4000000953674316) for decplaces in range(10)]
>
> ['4', '4.4', '4.40', '4.400', '4.4000', '4.40000', '4.400000',
> '4.4000001', '4.40000010', '4.400000095']
>
> HTH,
> John


another couples and round number corresponding to the right value

('\x00\x00\x00\x02', 5.8774717541114375e-039, '0.000')
('0\x8b\x01\x95', 1061222.0, '1061222.000')
('\xb8\x1e=\x83', 5.9099998474121094, '5.910')
(')\\O\x83', 6.4800000190734863, '6.480')
('\x9a\x99A\x83', 6.0500001907348633, '6.050')
('\x00\x00P\x83', 6.5, '6.500')
('8BY\x95', 1779783.0, '1779783.000')
('\x00\x00\x00\x02', 5.8774717541114375e-039, '0.000')
('\xe0\xa0\x02\x95', 1070108.0, '1070108.000')
('33{\x83', 7.8499999046325684, '7.850')
('q=z\x83', 7.820000171661377, '7.820')
('33s\x83', 7.5999999046325684, '7.600')
(')\\\x7f\x83', 7.9800000190734863, '7.980')
('\x00\x9aX\x92', 221800.0, '221800.000')
('\x00\x00\x00\x02', 5.8774717541114375e-039, '0.000')
('0\xa1\x02\x95', 1070118.0, '1070118.000')
('\x85\xebq\x83', 7.559999942779541, '7.560')
('\x14\xaeo\x83', 7.4899997711181641, '7.490')
('\xcd\xccT\x83', 6.6500000953674316, '6.650')
('\x00\x00p\x83', 7.5, '7.500')
('\x00\xa4N\x92', 211600.0, '211600.000')
('\x00\x00\x00\x02', 5.8774717541114375e-039, '0.000')
('\x90\xa1\x02\x95', 1070130.0, '1070130.000')
('\xaeGa\x83', 7.0399999618530273, '7.040')
('\xc3\xf5p\x83', 7.5300002098083496, '7.530')
('\x8f\xc2e\x83', 7.179999828338623, '7.180')
('H\xe1b\x83', 7.0900001525878906, '7.090')
('\xc0\xe27\x93', 376598.0, '376598.000')
('\x00\x00\x00\x02', 5.8774717541114375e-039, '0.000')
('\x08\xa4\x02\x95', 1070209.0, '1070209.000')
('\x9a\x99a\x83', 7.0500001907348633, '7.050')
('\xd7\xa3x\x83', 7.7699999809265137, '7.770')
('H\xe1r\x83', 7.5900001525878906, '7.590')
('{\x14v\x83', 7.690000057220459, '7.690')
('\x80.W\x93', 440692.0, '440692.000')
('\x00\x00\x00\x02', 5.8774717541114375e-039, '0.000')
('h\xa4\x02\x95', 1070221.0, '1070221.000')
('\x8f\xc2\x01\x84', 8.1099996566772461, '8.110')
('=\n\x03\x84', 8.1899995803833008, '8.190')
('\xcd\xcc\x00\x84', 8.0500001907348633, '8.050')
('ffv\x83', 7.6999998092651367, '7.700')
('\x80X\x1a\x94', 632200.0, '632200.000')
('\x00\x00\x00\x02', 5.8774717541114375e-039, '0.000')
('\x08\xa7\x02\x95', 1070305.0, '1070305.000')
('33s\x83', 7.5999999046325684, '7.600')
('q=r\x83', 7.570000171661377, '7.570')
('\\\x8fj\x83', 7.3299999237060547, '7.330')
('33k\x83', 7.3499999046325684, '7.350')
('\xc0a\r\x94', 579100.0, '579100.000')
('\x00\x00\x00\x02', 5.8774717541114375e-039, '0.000')
('X\xa7\x02\x95', 1070315.0, '1070315.000')
('\xcd\xcc|\x83', 7.9000000953674316, '7.900')
('q=z\x83', 7.820000171661377, '7.820')
('\x00\x00p\x83', 7.5, '7.500')
('\x00\x00p\x83', 7.5, '7.500')
('\x00\x1b7\x92', 187500.0, '187500.000')
('\x00\x00\x00\x02', 5.8774717541114375e-039, '0.000')
('\xb8\xa7\x02\x95', 1070327.0, '1070327.000')
('{\x14~\x83', 7.940000057220459, '7.940')
('\xcd\xcc\x04\x84', 8.3000001907348633, '8.300')
('\xe1z\x00\x84', 8.0299997329711914, '8.030')
('\xcd\xcc\x10\x84', 9.0500001907348633, '9.050')
('\x00R\x00\x95', 1051200.0, '1051200.000')
('\x00\x00\x00\x02', 5.8774717541114375e-039, '0.000')
('P\xaa\x02\x95', 1070410.0, '1070410.000')
('R\xb8\x1e\x84', 9.9200000762939453, '9.920')
('\xd7\xa3\x1c\x84', 9.7899999618530273, '9.790')
('\x85\xeb\x19\x84', 9.619999885559082, '9.620')
('\x9a\x99\x19\x84', 9.6000003814697266, '9.600')
('\x98\x1c\x0c\x95', 1147795.0, '1147795.000')
('\x00\x00\x00\x02', 5.8774717541114375e-039, '0.000')
('\xa0\xaa\x02\x95', 1070420.0, '1070420.000')
('=\n\x0f\x84', 8.9399995803833008, '8.940')
('ff\x0e\x84', 8.8999996185302734, '8.900')
('\xe1z\x0c\x84', 8.7799997329711914, '8.780')
('\x1f\x85\x0f\x84', 8.9700002670288086, '8.970')
('\x00\x1d&\x92', 170100.0, '170100.000')
('\x00\x00\x00\x02', 5.8774717541114375e-039, '0.000')
('8\xad\x02\x95', 1070503.0, '1070503.000')
('\xf6(\x0c\x84', 8.7600002288818359, '8.760')
('\xe1z\x14\x84', 9.2799997329711914, '9.280')


all is ok.
thank u