[squeak-dev] Re: [Pharo-dev] Float class comment
Marcus Denker
marcus.denker at inria.fr
Thu Nov 27 08:15:48 UTC 2014
I added an issue tracker entry
14536 Float class comment
https://pharo.fogbugz.com/f/cases/14536
> On 25 Nov 2014, at 18:42, Eliot Miranda <eliot.miranda at gmail.com> wrote:
>
> Hi All,
>
> who wrote the Float class comment? Two things,
>
> - first the comment mentions "I" and thanks several people, but there is no comment stamp to reveal the author. It would be lovely if the author could "sign" this comment
>
> - second, there seems to be a minor error (but I'm no expert), the comment states
>
> "It may help you to know that the basic format is...
> sign 1 bit
> exponent 11 bits with bias of 1023 (16r3FF) to produce an exponent
> in the range -1023 .. +1024
> - 16r000:
> significand = 0: Float zero
> significand ~= 0: Denormalized number (exp = -1024, no hidden '1' bit)
> - 16r7FF:
> significand = 0: Infinity
> significand ~= 0: Not A Number (NaN) representation
> mantissa 53 bits, but only 52 are stored (20 in the first word, 32 in the second). This is because a normalized mantissa, by definition, has a 1 to the right of its floating point, and IEEE-754 omits this redundant bit to gain an extra bit of precision instead. People talk about the mantissa without its leading one as the FRACTION, and with its leading 1 as the SIGNFICAND."
>
> But if the significand has a leading zero then surely the section in the middle should read
>
> sign 1 bit
> exponent 11 bits with bias of 1023 (16r3FF) to produce an exponent
> in the range -1023 .. +1024
> - 16r000:
> mantissa = 0: Float zero
> mantissa ~= 0: Denormalized number (exp = -1024, no hidden '1' bit)
> - 16r7FF:
> mantissa = 0: Infinity
> mantissa ~= 0: Not A Number (NaN) representation
>
> Right?
> --
> best,
> Eliot
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