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Re: Is 1111 1110 10 equal to 0xfe80 or 0x3fa?

Bob Hinden <bob.hinden@gmail.com> Thu, 06 June 2019 17:45 UTC

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Subject: Re: Is 1111 1110 10 equal to 0xfe80 or 0x3fa?
From: Bob Hinden <bob.hinden@gmail.com>
In-Reply-To: <a71b00b7-0e0c-242a-b3f7-147f4c6b2eb0@gmail.com>
Date: Thu, 06 Jun 2019 10:44:58 -0700
Cc: Bob Hinden <bob.hinden@gmail.com>, IPv6 List <ipv6@ietf.org>
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To: Alexandre Petrescu <alexandre.petrescu@gmail.com>
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> On Jun 6, 2019, at 10:18 AM, Alexandre Petrescu <alexandre.petrescu@gmail.com> wrote:
> 
> Hi 6MANners,
> 
> In private discussion we disagree about this point:
> 
> I maintain that 1111 1110 10 equals 0x3fa, because that's what my Windows Calculator says: I type 1111 1110 10 and it converts to 0x3fa.

The binary string 1111111010 is indeed 0x3FA.  A binary to hex calculator right justifies it, so it is converting 001111111010.

When used as a prefix it is 0xFE8.  In that case it is left justified.

Bob


> 
> On another hand, I am rhetorically asked how can 1111 1110 10 be 0x3fa?
> 
> (the 1111 1110 10 are the 10 leading bits of the IPv6 link local addresses, which is familiarly known to start with an fe80).
> 
> On my side, this is a difficulty to understand this 0xfe80, especially since 1111 1110 10 is so printed in Figure in RFC4291.
> 
> Alex
> 
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