As far as I know, Ruby's Fixnum is 30-bit signed integer.
One bit is used as a flag for whether it's a direct value.
Another bit is used for non-Fixnum direct values.
I wondered how Fixnum#[] works and tested it.
def show_binary(i)
result = ''
32.times do |b|
result = i[b].to_s + result
if (b % 8 == 7) and (b != 31)
result = " " + result
end
end
puts result + ": " + i.to_s
end
This is exactly how 32-bit signed integer's binary representations look
like.
My guess is that Fixnum#[] works as if it's 32-bit signed integer.
It's not showing its real binary representation.
Is my guess true?
My another question is that even if (2 ** 31 - 1) is not a Fixnum, the
above code works for it (Actually Bignum#[]).
If the number is bigger than that, [] doesn't work.
Fixnum#[] and Bignum#[] are cleverly hiding the internal facts and are
made to simulate 32-bit signed integers?
As far as I know, Ruby's Fixnum is 30-bit signed integer.
One bit is used as a flag for whether it's a direct value.
Another bit is used for non-Fixnum direct values.
I wondered how Fixnum# works and tested it.
look like.
My guess is that Fixnum# works as if it's 32-bit signed integer.
It's not showing its real binary representation.
Is my guess true?
Yes.
My another question is that even if (2 ** 31 - 1) is not a Fixnum, the
above code works for it (Actually Bignum#).
If the number is bigger than that, doesn't work.
For which numbers do you have problems? I don't see any so far
As far as I know, Ruby's Fixnum is 30-bit signed integer.
One bit is used as a flag for whether it's a direct value.
Another bit is used for non-Fixnum direct values.
I wondered how Fixnum# works and tested it.
def show_binary(i)
result = ''
32.times do |b|
result = i[b].to_s + result
if (b % 8 == 7) and (b != 31)
result = " " + result
end
end
puts result + ": " + i.to_s
end
email :: ara [dot] t [dot] howard [at] noaa [dot] gov
phone :: 303.497.6469
renunciation is not getting rid of the things of this world, but accepting
that they pass away. --aitken roshi
Also, a Fixnum always has an odd object_id, while any other VALUE has an even object_id.
···
On 04 May 2005, at 09:04, camsight@gmail.com wrote:
Hi, people!
As far as I know, Ruby's Fixnum is 30-bit signed integer.
One bit is used as a flag for whether it's a direct value.
Another bit is used for non-Fixnum direct values.
My guess is that Fixnum# works as if it's 32-bit signed integer.
It's not showing its real binary representation.
Is my guess true?
For which numbers do you have problems? I don't see any so far
I mean...
If Bignum# is made to simulate 32-bit signed integers, it can't show
numbers with more than 32-bit representation.
Well, positive numbers will be okay.
But what about negative numbers?
When can I expect the sign bit?
I assume that numbers beyond 32-bit are not suitable for Bignum#.
Do you agree?
IIUC, it's not precisely a "sign bit"; it's more like an entire
bit-flip. -1 is zero, bit-flipped. So if you are trying to use
Integer# to get determine the sign of a number, the question is
simply: how high do you want to go? integer[512] will correctly
determine sign for numbers in the range of (-(2**512-1)..2**512) (that
is, a 512 bit integer). There no way (that I can think of) to use
Integer# to return the correct sign on *any* integer usable in Ruby.
hth,
Mark
···
On 5/4/05, camsight@gmail.com <camsight@gmail.com> wrote:
Thanks, Robert!
> For which numbers do you have problems? I don't see any so far
I mean...
If Bignum# is made to simulate 32-bit signed integers, it can't show
numbers with more than 32-bit representation.
Well, positive numbers will be okay.
But what about negative numbers?
When can I expect the sign bit?
I assume that numbers beyond 32-bit are not suitable for Bignum#.
Do you agree?
<camsight@gmail.com> schrieb im Newsbeitrag news:1115223668.955656.66750@o13g2000cwo.googlegroups.com...
Thanks, Robert!
For which numbers do you have problems? I don't see any so far
I mean...
If Bignum# is made to simulate 32-bit signed integers, it can't show
numbers with more than 32-bit representation.
Well, positive numbers will be okay.
But what about negative numbers?
When can I expect the sign bit?
Well, since Bignums can be arbitrary size, you have to decide. The values returned by Fixnum# and Bignum# represent bits of a two complement's arbitrary size binary number. If you view it from this perspective, you'll see that there is no single sign bit. Negative numbers have *all* the higher bits set to 1.
I assume that numbers beyond 32-bit are not suitable for Bignum#.
Do you agree?
Btw, you'll notice the same effect with Fixnum# - because these methods do not represent the actual binary representation in mem but try to represent the general concept of signed binary numbers:
In article <de63abca05050410051035e0c2@mail.gmail.com>,
···
Mark Hubbart <discordantus@gmail.com> wrote:
On 5/4/05, camsight@gmail.com <camsight@gmail.com> wrote:
Thanks, Robert!
> For which numbers do you have problems? I don't see any so far
I mean...
If Bignum# is made to simulate 32-bit signed integers, it can't show
numbers with more than 32-bit representation.
Well, positive numbers will be okay.
But what about negative numbers?
When can I expect the sign bit?
I assume that numbers beyond 32-bit are not suitable for Bignum#.
Do you agree?
IIUC, it's not precisely a "sign bit"; it's more like an entire
bit-flip. -1 is zero, bit-flipped.
Guy's this is very neat and it also brings back some memories.
Some years ago I did quite a lot of programming on CDC 6600 & 7600 at the
ULCC. These machines use exactly the same notation. I remember revelling in
having two zeros because I used to use one to mean null (-1) and the other
zero. Yes programming in FORTRAN and writing COMPASS assembler subroutines
when FORTRAN was stumped. Mmm about 1974-1976 I think.
Kind regards,
Andrew Ballantine
···
----- Original Message -----
From: "Robert Klemme" <bob.news@gmx.net>
Newsgroups: comp.lang.ruby
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
Sent: Wednesday, May 04, 2005 6:09 PM
Subject: Re: Fixnum's binary representation
<camsight@gmail.com> schrieb im Newsbeitrag
news:1115223668.955656.66750@o13g2000cwo.googlegroups.com...
> Thanks, Robert!
>
>> For which numbers do you have problems? I don't see any so far
>
> I mean...
> If Bignum# is made to simulate 32-bit signed integers, it can't show
> numbers with more than 32-bit representation.
> Well, positive numbers will be okay.
> But what about negative numbers?
> When can I expect the sign bit?
Well, since Bignums can be arbitrary size, you have to decide. The values
returned by Fixnum# and Bignum# represent bits of a two complement's
arbitrary size binary number. If you view it from this perspective,
you'll
see that there is no single sign bit. Negative numbers have *all* the
higher bits set to 1.
> I assume that numbers beyond 32-bit are not suitable for Bignum#.
> Do you agree?
yeah! that's what it is. IANACSM (I am not a CS major) and I still
have terminology to learn. I am woefully ignorant of it, and really
should read some programming theory. When I get the time.
cheers,
Mark
···
On 5/4/05, Phil Tomson <ptkwt@aracnet.com> wrote:
In article <de63abca05050410051035e0c2@mail.gmail.com>,
Mark Hubbart <discordantus@gmail.com> wrote:
>On 5/4/05, camsight@gmail.com <camsight@gmail.com> wrote:
>> Thanks, Robert!
>>
>> > For which numbers do you have problems? I don't see any so far
>>
>> I mean...
>> If Bignum# is made to simulate 32-bit signed integers, it can't show
>> numbers with more than 32-bit representation.
>> Well, positive numbers will be okay.
>> But what about negative numbers?
>> When can I expect the sign bit?
>> I assume that numbers beyond 32-bit are not suitable for Bignum#.
>> Do you agree?
>
>IIUC, it's not precisely a "sign bit"; it's more like an entire
>bit-flip. -1 is zero, bit-flipped.
