Next float?

Mark Dickinson dickinsm at gmail.com
Thu Nov 22 23:41:01 CET 2007


On Nov 21, 11:48 pm, "Mark T" <nos... at nospam.com> wrote:
> Here's some functions to get the binary representation of a float.  Then
> just manipulate the bits (an exercise for the reader):
>
> import struct
>
> def f2b(f):
>     return struct.unpack('I',struct.pack('f',f))[0]
>
> def b2f(b):
>     return struct.unpack('f',struct.pack('I',b))[0]
>
> >>> f2b(1.0)
> 1065353216
> >>> hex(f2b(1.0))
> '0x3f800000'
> >>> b2f(0x3f800000)
> 1.0
> >>> b2f(0x3f800001)
> 1.0000001192092896
> >>> b2f(0x3f7fffff)
>
> 0.99999994039535522

And it's worth noting that thanks to the way the floating-point format
is designed, the 'bit-twiddling' is actually just a matter of adding
or subtracting one from the integer representation above.  This works
all the way from zero, through subnormals, up to and including
infinities.

Mark (but not the same Mark)



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