zero fill with pack

Spooky has asked for the wisdom of the Perl Monks concerning the following question:

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Re: zero fill with pack by ikegami (Patriarch) on Jun 22, 2010 at 16:48 UTC
I'd like to use the "pack" function to produce what hoepfully will appear as "00 00 00 00 00 09 fe 00" when viewed in emacs with the "hexl-mode" turned on. That's a 64-bit int, so `pack('q>', $_); # Signed pack('Q>', $_); # Unsigned` [download] "`>`" requires 5.10 (IIRC). "`q`" and "`Q`" require a 64-bit support. If you don't have a 64-bit support and your numbers aren't "very" large (<2³²), you could fake it using `pack('NN', $_<0 ? -1 : 0, $_); # Signed pack('NN', 0, $_); # Unsigned` [download] In using "pack" I need to figure out how to fill with spaces ("\x20") before the actual hex representation of the 654848. Any suggestions? You were talking about converting a number to a native int, now you're talking about its hex representation. It's not clear what you're asking here. Assuming this is a completely separate question, `sprintf('%8X', $_); # Padded with spaces sprintf('%08X', $_); # Padded with zeros` [download] Update: Added answer to second question.	[reply] [d/l] [select]
Re^2: zero fill with pack by Spooky (Beadle) on Jun 22, 2010 at 18:03 UTC
Ikegami, The 'NN' "fake-out" worked nicely. Two things though, I also need to pad the above value with two spaces, i.e., "00 00 00 00 00 09 fe 00 20 20" - need a total byte displacement of ten: how can I pad/add two more spaces at the end of my value? And, what is the significance of the ", 0," in the "pack('NN', 0, $_)" statement? Again, thanks for your prompt response!	[reply]
Re^3: zero fill with pack by ikegami (Patriarch) on Jun 22, 2010 at 18:34 UTC
what is the significance of the ", 0," in the "pack('NN', 0, $_)" statement? The value for the first "N". `Q=654848 ----------------------- 00 00 00 00 00 09 fe 00 ----------- ----------- N=0 N=654848` [download] I also need to pad the above value with two spaces, i.e., "00 00 00 00 00 09 fe 00 20 20" More concisely, you want to add two spaces. pack: `C An unsigned char (octet) value. A A text (ASCII) string, will be space padded.` [download] `pack('NN CC', 0, $_, ord(' '), ord(' ')) pack('NN CC', 0, $_, 0x20, 0x20) pack('NN A2', 0, $_, ' ') pack('NN n', 0, $_, 0x2020)` [download]	[reply] [d/l] [select]
Re^4: zero fill with pack by Spooky (Beadle) on Jun 23, 2010 at 16:54 UTC
Re^4: zero fill with pack by Spooky (Beadle) on Jun 25, 2010 at 13:21 UTC
Re^5: zero fill with pack by Spooky (Beadle) on Jun 25, 2010 at 15:28 UTC
Re^2: zero fill with pack by BrowserUk (Patriarch) on Jun 22, 2010 at 21:54 UTC
Your 32-bit solution is deficient. In that it fails for the 9 quadrillion integers between 232 ad 253 that 32-bit Perls can happily represent.	[reply]
Re: zero fill with pack by BrowserUk (Patriarch) on Jun 22, 2010 at 16:46 UTC
Note: The `print unpack 'H',` is just a simulation of hexl-mode. It's the pack bit which does the work: `print unpack 'H', pack 'Q>', 654848;; 000000000009fe00 ## With a Perl that doesn't support 64-bit ints (Q). ## Corrected &.v.% per ikegami++ print unpack 'H', pack 'NN', int( $n / 2*32 ), $n % 0xffffffff;; 000000000009fe00` [download]	[reply] [d/l] [select]
Re^2: zero fill with pack by ikegami (Patriarch) on Jun 22, 2010 at 16:51 UTC
`$n & 0xffffffff` won't work. You need `$n % 0xffffffff`.	[reply] [d/l] [select]
Re^3: zero fill with pack by BrowserUk (Patriarch) on Jun 22, 2010 at 16:53 UTC
Works for my (64-bit) Perl ;)	[reply]
Re^4: zero fill with pack by ikegami (Patriarch) on Jun 22, 2010 at 17:10 UTC