Bit twiddling floating point numbers

[Blubaugh, David A.]

Sorry for the reply.  I did not get your message until now.  I was
wondering if there was a way to develop floating-point mathematics
package within a module.  I was wondering if some of your work on bit
twiddling floating - point numbers could be provided to me!!!  Thanks.  
 
 
David Blubaugh
 
 

________________________________

From: Jeff Goldfinkle [mailto:jeff.goldfinkle at gmail.com] 
Sent: Monday, April 28, 2008 2:10 PM
To: Blubaugh, David A.
Subject: Re: Bit twiddling floating point numbers


sure - go right ahead


On Mon, Apr 28, 2008 at 8:17 PM, Blubaugh, David A.
<dblubaugh at belcan.com> wrote:


	Are you still out there?  
	 
	 
	Can I still ask you about my question?
	 
	 
	thanks,
	 
	David
	 
	 

________________________________

	From: Jeff Goldfinkle [mailto:jeff.goldfinkle at gmail.com] 
	Sent: Friday, March 07, 2008 1:04 AM
	To: Blubaugh, David A. 

	Subject: Re: Bit twiddling floating point numbers
	

	Hi David
	
	Sure. I'm not sure what help I can be, but ask away.
	
	Jeff
	
	
	
	
	On Thu, Mar 6, 2008 at 11:25 PM, Blubaugh, David A.
<dblubaugh at belcan.com> wrote:
	

		Jeff,
		
		
		Hello.  This idea or representing a float with long
seems to be
		extremely interesting.  I am currently utilizing the
MyHDL environment
		to map algorithms to hardware.  May I ask you more
questions in order to
		map integer mathematics to emulate floating -point
mathematics, in order
		to maybe develop efficient pseudo-floating-point
hardware??
		
		 Thanks,
		
		David Blubaugh
		
		
		
		
		
		-----Original Message-----
		From: Jeff.Goldfinkle at gmail.com
[mailto:Jeff.Goldfinkle at gmail.com]
		Sent: Thursday, March 06, 2008 4:01 PM
		To: python-list at python.org
		Subject: Re: Bit twiddling floating point numbers
		
		On Mar 6, 11:00 am, Bryan Olson
<fakeaddr... at nowhere.org> wrote:
		> Mark Dickinson wrote:
		
		> > Jeff Goldfin wrote:
		> >> I can pack and unpack a float into a long e.g.
		> >> struct.unpack('I',struct.pack('f',0.123))[0]
		> >> but then I'm not sure how to work with the
resulting long.
		>
		> >> Any suggestions?
		>
		
		> > One alternative to using struct is to use math.ldexp
and math.frexp:
		>
		> >>>> m, e = frexp(pi)
		> >>>> m
		> > 0.78539816339744828
		> >>>> e
		> > 2
		> >>>> int(m*2**53)
		> > 7074237752028440L
		>
		> > Then you can do your bit twiddling on int(m*2**53),
before using
		> > ldexp to 'repack' the float.
		>
		> Ah, those are handy. Jeff described his problem: "In
particular, I
		
		> would like to round my float to the n most significant
bits."
		
		> I think this works:
		>
		>    from math import frexp, ldexp, floor
		>
		>    def round_mantissa(x, nbits):
		>        shifter = 1 << nbits
		>        (m, e) = frexp(x)
		>        m = floor(m * shifter + 0.5) / shifter
		>        return ldexp(m, e)
		>
		> --
		> --Bryan
		Thanks for the help - your function seems to fit the
bill even better
		than gmpy since I don't need an external module. In my
case I'll use m =
		floor(m * shifter) / shifter instead of m = floor(m *
shifter +
		0.5) / shifter
		
		Jeff
		
		
		
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