Re^3: Bit order in bytes

Actually, it's the same results - these templates apparently know whether they're on a big-endian or little-endian machine, and adjust themselves accordingly to standardise the output.

Hm. That is a surprise.

Now I am really confused by the apparent nybble swapping:

print unpack 'b*', "\x12\x34";;
0100 1000 0010 1100
   2    1    4    3

print unpack 'B*', "\x12\x34";;
0001 0010 0011 0100
   1    2    3    4

print unpack 'b*', pack 'v', 0x1234;;
0010 1100 0100 1000
   4    3    2    1

print unpack 'b*', pack 'n', 0x1234;;
0100 1000 0010 1100
   2    1    4    3
[download]

I can't make sense of that at all.

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

Comment on Re^3: Bit order in bytes Download Code

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Re^4: Bit order in bytes by syphilis (Archbishop) on Dec 10, 2013 at 13:38 UTC
Your `pack 'v'` and `pack 'n'` arrange the bytes in reverse order - and `unpack 'b'` just unpacks them both from the same end ... hence the bytes come out in the reverse order - but each byte is read in ascending bit order, in accordance with the 'b' template spec. Where you're unpacking the `\x12\x34`, that's also correct. Both 'b' and 'B*' read the bytes in the same order, but read those bytes from opposing ends. I don't think there's any nybble-swapping. You've just got one byte that's read either as `01001000` or (reversed) `00010010` (depending upon the template) - and another byte that's being read as either `00101100` or (reversed) `00110100` (depending upon the template). ... I think ... Cheers, Rob	[reply] [d/l] [select]
Re^5: Bit order in bytes by BrowserUk (Patriarch) on Dec 10, 2013 at 14:15 UTC
I did say "apparent* nybble swapping"* :) Its one of those things that has caused me to look twice on many occasions, but never caused me enough concern nor affected anything I was doing, to require investigation. Now looking at it, it becomes clear that it just comes down to the fact that when we right `"\x12"`, we write the high nybble 0x1 before the low nybble 0x2. Thus, when it is displayed with 'b', lsb -> msb, the digits appear to swap places. Another red-herring laid bare :) With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l]
Re^4: Bit order in bytes by hdb (Monsignor) on Dec 10, 2013 at 13:03 UTC
Not sure about your statement on swapping but I cannot see any. hex 12 is decimal 18 = 16 + 2 is binary 00010010 and hex 34 is decimal 52 is binary 00110100. `print unpack 'b', "\x12\x34";; 01001000 00101100 18 52 print unpack 'B', "\x12\x34";; 00010010 00110100 18 52` [download]	[reply] [d/l]
Re^5: Bit order in bytes by BrowserUk (Patriarch) on Dec 10, 2013 at 13:10 UTC
Nybbles == 4-bits, so looking at the byte values in decimal doesn't show it. Look at the patterns of the nybbles (in hex): `## 'b' lists bits lsb->msb print unpack 'b', "\x12\x34";; 1248 1248 1248 1248 0100 1000 0010 1100 2 1 4 3 ## 'B' lists bits msb <- lsb print unpack 'B', "\x12\x34";; 8421 8421 8421 8421 0001 0010 0011 0100 1 2 3 4` [download] With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l]