Thanks Steve and David!
To follow up on Steve's example ...
The input is: 01011001
With this element declaration:
<xs:element name="bit3"
type="xs:int"
dfdl:length="3"
dfdl:bitOrder="mostSignificantBitFirst"... />
The value of <bit3> will be binary 010 (decimal 2), right?
With this element declaration:
<xs:element name="bit3"
type="xs:int"
dfdl:length="3"
dfdl:bitOrder="leastSignificantBitFirst"... />
The value of <bit3> will be binary 001 (decimal 1), right?
That is not the behavior that I got with my tests.
/Roger
-----Original Message-----
From: Steve Lawrence <[email protected]>
Sent: Friday, February 15, 2019 8:50 AM
To: [email protected]; David Winant <[email protected]>
Subject: Re: [EXT] Re: I don't understand bitOrder - please help!
That's correct. As a minimal example, let's imagine we had one byte of data
like so, with bits labels A-H:
Label: ABCDEFGH
Bits: 01011001
Imagine we had an element like so:
<xs:element name="bit3" type="xs:int" dfdl:length="3" ... />
So an integer with length 3 bits.
With bitOrder = MSBF, we would read the 3 most significant bits first.
So bits A-C and a value of 2 (010). If there was a following element, the next
bit read would be bit D.
With bitOrdre = LSBF, we would read the 3 least significant bits first.
So bits F-H and a value of 1 (001). If there was a following element, the next
bit read would be bit E.
On 2/15/19 8:33 AM, David Winant wrote:
> Roger,
>
> "Most significant" is implied as leftmost because that is the way we
> write numbers. It means the bit associated with the highest power of
> 2, 2^7 in the case of a byte.
>
> What the bitOrder controls is whether the "first" bit is read from the
> right or read from the left.
>
> David
>
> On Fri, Feb 15, 2019 at 8:13 AM Costello, Roger L. <[email protected]
> <mailto:[email protected]>> wrote:
>
> Hi Mike,____
>
> __ __
>
> * Least significant bit first or LSBF, the first bit is the rightmost
> zero.____
>
> __ __
>
> So the most significant bit is the leftmost one.____
>
> __ __
>
> * Most significant bit first, MSBF, the first bit is the 1 on
> the left.____
>
> __ __
>
> So the least significant bit is the rightmost zero.____
>
> __ __
>
> Aren't they saying the same thing: The most significant bit is the
> leftmost
> one and the least significant bit if the rightmost zero. What's the
> value/benefit/use-case of specifying bitOrder? ____
>
> __ __
>
> /Roger____
>
> __ __
>
> *From:* Beckerle, Mike <[email protected]
> <mailto:[email protected]>>
> *Sent:* Friday, February 15, 2019 8:02 AM
> *To:* [email protected] <mailto:[email protected]>
> *Subject:* [EXT] Re: I don't understand bitOrder - please
> help!____
>
> __ __
>
> Probably bit order should have been called bit numbering system.
> ____
>
> It does nothing for whole bytes.____
>
> It is only about which bits are considered to occupy which index
> positions. ____
>
> So given byte with value 128, base 2 that is 80 hex or 10000000. So is the
> "first" bit a 1 or a zero?____
>
> Least significant bit first or LSBF, the first bit is the rightmost zero.
> Most significant bit first, MSBF, the first bit is the 1 on the
> left. ____
>
> Many format standards describe the bits numbering from right to left.
>
>
>
>
> ____
>
> Get Outlook for Android <https://aka.ms/ghei36>____
>
> __ __
>
>
> ----------------------------------------------------------------------
> ----------
>
> *From:*Costello, Roger L. <[email protected] <mailto:[email protected]>>
> *Sent:* Friday, February 15, 2019 7:33:29 AM
> *To:* [email protected] <mailto:[email protected]>
> *Subject:* I don't understand bitOrder - please help! ____
>
> ____
>
> Hello DFDL community,____
>
> ____
>
> I've read the portions of the specification that discuss bitOrder.
> I'm lost.____
>
> ____
>
> I ran some tests to get a feel for the difference between
> leastSignificantBitFirst and mostSignificantBitFirst. See below. Based on
> my
> tests, it appears there is no difference between leastSignificantBitFirst
> and mostSignificantBitFirst. Would you explain what this bitOrder stuff is
> all about, please? /Roger____
>
> ____
>
> ____
>
>
>
> --
>
> David Winant |*Trident Systems Incorporated *Sr. Software Engineer,
> Integrated Systems Engineering Group
> 10201 Fairfax Boulevard
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