convert floats to their 4 byte representation

[godavemon]

I need to take floats and dump out their 4 byte hex representation.
This is easy with ints with the built in hex function or even better
for my purpose

def hex( number, size ):
s = "%"+str(siz e) + "X"
return (s % number).replace (' ', '0')

but I haven't been able to find anything for floats. Any help would be
great.

[Alex Martelli]

Re: convert floats to their 4 byte representation

godavemon <davefowler@gma il.com> wrote:
[color=blue]
> I need to take floats and dump out their 4 byte hex representation.
> This is easy with ints with the built in hex function or even better
> for my purpose
>
> def hex( number, size ):
> s = "%"+str(siz e) + "X"
> return (s % number).replace (' ', '0')
>
> but I haven't been able to find anything for floats. Any help would be
> great.[/color]

floats' internal representation in Python is 8 bytes (equivalent to a C
"double"). However, you can import struct and use struct.pack('f' ,x) to
get a 4-byte ("single precision") approximation of x's 8-byte value,
returned as a string of 4 bytes; you may force little-endian by using as
the format '<f' or big-endian by using '>f'; then loop on each character
of the string and get its ord(c) [a number from 0 to 255] to format as
you wish.

For example

import struct
def float_hex4(f):
return ''.join(('%2.2x '%ord(c)) for c in struct.pack('f' , f))

or variants thereof.


Alex

[Tim Chase]

Re: convert floats to their 4 byte representation

> s = "%"+str(siz e) + "X"[color=blue]
> return (s % number).replace (' ', '0')[/color]

While I don't have a fast and easy way to represent floats, you
may want to tweak this to be

return ("%0*X" % (size,number))

which will zero-pad the number in hex to "size" number of places
in a single step. It also helps prevent problems where there might
[color=blue]
> but I haven't been able to find anything for floats. Any help
> would be great.[/color]

My first stab at such an attempt:
[color=blue][color=green][color=darkred]
>>> from struct import pack, unpack
>>> s = pack("d", 3.14)
>>> i = unpack("q", s)
>>> "%X"%i[/color][/color][/color]
'40091EB851EB85 1F'[color=blue][color=green][color=darkred]
>>> def floatAsHex(f, size):[/color][/color][/color]
.... return "%0*X" % (size, unpack("q", pack("d", f))[0])
....[color=blue][color=green][color=darkred]
>>> floatAsHex(3.14 , 20)[/color][/color][/color]
'000040091EB851 EB851F'

It's ugly, it's hackish, it's likely architecture-dependant, but
it seems to do what you're describing.

-tkc

[Grant Edwards]

Re: convert floats to their 4 byte representation

On 2006-06-14, godavemon <davefowler@gma il.com> wrote:
[color=blue]
> I need to take floats and dump out their 4 byte hex representation.[/color]

struct

--
Grant Edwards grante Yow! Darling, my ELBOW
at is FLYING over FRANKFURT,
visi.com Germany...

[Scott David Daniels]

Re: convert floats to their 4 byte representation

godavemon wrote:[color=blue]
> I need to take floats and dump out their 4 byte hex representation.
> This is easy with ints with the built in hex function or even better
> for my purpose
>
> def hex( number, size ):
> s = "%"+str(siz e) + "X"
> return (s % number).replace (' ', '0')[/color]

This should be a trifle nicer:
def hexx(number, size): # don't shadow the "hex" builtin
s = "%0s" + str(size) + "X"
return s % number
[color=blue]
> but I haven't been able to find anything for floats. Any help would be
> great.[/color]

Getting to float bytes is tougher.
First, python Floats are C Doubles, so you probably mean 8=byte hex.

import array

def eights(number, swap=False):
data = array.array('d' , [number])
if swap:
data.byteswap()
return ' '.join(hexx(ord (char), 2) for char in data.tostring() )

def fours(number, swap=False):
data = array.array('f' , [number])
if swap:
data.byteswap()
return ' '.join(hexx(ord (char), 2) for char in data.tostring() )

--Scott David Daniels
scott.daniels@a cm.org

[godavemon]

Re: convert floats to their 4 byte representation

I've been a member for a while but I had no idea how helpful this form
is. I had a one hour meeting and when I came back there were 4
replies. Thanks for your help!


Scott David Daniels wrote:[color=blue]
> godavemon wrote:[color=green]
> > I need to take floats and dump out their 4 byte hex representation.
> > This is easy with ints with the built in hex function or even better
> > for my purpose
> >
> > def hex( number, size ):
> > s = "%"+str(siz e) + "X"
> > return (s % number).replace (' ', '0')[/color]
>
> This should be a trifle nicer:
> def hexx(number, size): # don't shadow the "hex" builtin
> s = "%0s" + str(size) + "X"
> return s % number
>[color=green]
> > but I haven't been able to find anything for floats. Any help would be
> > great.[/color]
>
> Getting to float bytes is tougher.
> First, python Floats are C Doubles, so you probably mean 8=byte hex.
>
> import array
>
> def eights(number, swap=False):
> data = array.array('d' , [number])
> if swap:
> data.byteswap()
> return ' '.join(hexx(ord (char), 2) for char in data.tostring() )
>
> def fours(number, swap=False):
> data = array.array('f' , [number])
> if swap:
> data.byteswap()
> return ' '.join(hexx(ord (char), 2) for char in data.tostring() )
>
> --Scott David Daniels
> scott.daniels@a cm.org[/color]

[Cameron Laird]

Re: convert floats to their 4 byte representation

In article <1150301012.403 651.198440@g10g 2000cwb.googleg roups.com>,
godavemon <davefowler@gma il.com> wrote:[color=blue]
>I've been a member for a while but I had no idea how helpful this form
>is. I had a one hour meeting and when I came back there were 4
>replies. Thanks for your help!
>
>
>Scott David Daniels wrote:[color=green]
>> godavemon wrote:[color=darkred]
>> > I need to take floats and dump out their 4 byte hex representation.[/color][/color][/color]