[Numpy-discussion] Custom floating point representation to IEEE 754 double

Daniele Nicolodi daniele at grinta.net
Tue Feb 25 19:35:23 EST 2014

On 26/02/2014 00:12, Oscar Benjamin wrote:
> On 25 February 2014 11:08, Daniele Nicolodi <daniele at grinta.net> wrote:
>> Hello,
>> I'm dealing with an instrument that transfers numerical values through
>> an RS232 port in a custom (?) floating point representation (56 bits, 4
>> bits exponent and 52 bits significand).
>> Of course I need to convert this format to a standard IEEE 754 double to
>> be able to do anything useful with it.  I came up with this simple code:
> My first approach would be that if you have an int and you want it as
> bits then you can use the bin() function e.g.:
>>>> bin(1234)
> '0b10011010010'
> You can then slice and reconstruct as ints with
>>>> int('0b101', 2)
> 5

How would that be helpful?  I believe it is much more computationally
expensive than relying on simple integer math, especially in the optics
of cythonization.

> Similarly my first port of call for simplicity would be to just do
> float(Fraction(mantissa, 2**exponent)). It doesn't really lend itself
> to cythonisation but it should be accurate and easy enough to
> understand.

"simpler" in my original email has to be read as involving less
operations and thus more efficient, not simpler to understand, indeed it
is already a simple implementation of the definition. What I would like
to know is if there are some smart shortcuts to make the computation
more efficient.


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