[DGD] Perfect dump of float

[Jared Maddox]

On Sat, May 28, 2011 at 12:22 AM, Jared Maddox <absinthdraco at gmail.com> wrote:
>> Date: Thu, 26 May 2011 23:42:21 -0700
>> From: Shentino <shentino at gmail.com>
>> To: "All about Dworkin's Game Driver" <dgd at dworkin.nl>
>> Subject: [DGD] Perfect dump of float
>> Message-ID: <BANLkTimm1C6VE=3mTQXgGG1zPvo3wcjtsg at mail.gmail.com>
>> Content-Type: text/plain; charset=UTF-8
>>
>> Since it's not possible to access the raw bit pattern, I was curious.how one
>> might dump a perfect representation of a float that doesn't result in even
>> one bit of data to be lost.
>>
>> My guess is that one would need to do some sort of ldexp to split the
>> mantissa and exponent apart, then use float.h for information on how many
>> fraction bits to extract from the mantissa for dumping out as hex.
>
> My advice is to divide it into two pieces (mantissa and exponent will
> work), convert both to integers (example: if your mantissa is an 8 bit
> unsigned fraction, then your integer is 255 * mantissa, if signed then
> 127 * mantissa), and use the integers. I originally came up with this
> for streaming floats over networks; due to it's purely-mathematical
> basis, it should work for every language with a function that splits
> floats into purely-integer and/or purely-fractional parts.
>

Oops, math mistake. Unless your 'fractional bits' can be equal to 1.0,
the correct values for 8-bit precision would be 256 for unsigned and
128 for signed, otherwise you'd get slightly LESS than 8-bit
precision.