From: Logan Capaldo <logancapaldo@...>
Date: 2006-06-12T04:26:03+09:00
Subject: Re: Converting a Float back to bytes


On Jun 9, 2006, at 5:44 PM, Harris Reynolds wrote:

> This is good stuff.  I am now getting the correct Float object  
> (21.0) from a string of bytes ("@5\000\000\000\000\000\000").   
> Now... here is a question... is there an easy way to go from the  
> Float back to bytes.  This seems like it may be much more difficult.
>
> something like this...
>
> float_object = 21.0
> bytes = SOME_API_HERE.convert(float_object)
>
> I think a result of this work I am doing should be a general  
> purpose BitConverter class similar to what .Net offers.  This would  
> make working with binary data in Ruby much less painful.
>
> thanks for any help,
>
> ~harris
>
> p.s.  Mike... thanks a bunch for the help on going from Bytes to a  
> Float!!!  I owe you... are you going to be at RailsConf?
>
>
>
> ----- Original Message ----
> From: Mike Stok <mike@stok.ca>
> To: ruby-talk ML <ruby-talk@ruby-lang.org>
> Sent: Thursday, June 8, 2006 10:49:36 PM
> Subject: Re: Converting 8 bytes to a Float
>
>
> On 8-Jun-06, at 10:39 PM, Harris Reynolds wrote:
>
>> Mike... thanks for the tip.  My mileage is varying though... here
>> is the same irb session on my machine:
>>
>> irb(main):004:0> s = ""
>> => ""
>> irb(main):005:0> s << 64 << 53 << "\0" * 6
>> => "@5\000\000\000\000\000\000"
>> irb(main):006:0> s.unpack('D')
>> => [6.73510288410787e-320]
>>
>> I'm not getting the clean result for some reason.
>>
>
> I'm on a PowerPC, and you're probably on an x86.  Our endian-ness is
> different.
>
> D uses native format to unpack the bytes, if your bytes are laid out
> the way you said they are then you probably want to use G which is
> specifically "big endian".
>
> See http://en.wikipedia.org/wiki/Endian for more background.
>
> Hope this helps,
>
> Mike
>
> -- 
> Mike Stok <mike@stok.ca>
> http://www.stok.ca/~mike/
>
> The "`Stok' disclaimers" apply.

[21.0].pack("D") no?