Re: 3-byte representation

Replies are listed 'Best First'.
Re^2: 3-byte representation by BrowserUk (Patriarch) on Oct 12, 2011 at 18:32 UTC
Hm? Big-endian: `sub pack24{ substr( pack('l>', $_[0]), 1) };; sub unpack24{ unpack('l>', "$_[0]\0") };; print "$_: ", unpack24( pack24( $_ ) ) for ( -8388608, -8388607, -2, -1, 0, 1, 2, 8388606, 8388607 );; -8388608: -2147483648 -8388607: -2147483392 -2: -512 -1: -256 0: 0 1: 256 2: 512 8388606: 2147483136 8388607: 2147483392` [download] Little-endian: `sub pack24{ substr( pack('l<', $_[0]), 1) };; sub unpack24{ unpack('l<', "$_[0]\0") };; print "$_: ", unpack24( pack24( $_ ) ) for ( -8388608, -8388607, -2, -1, 0, 1, 2, 8388606, 8388607 );; -8388608: 16744448 -8388607: 16744448 -2: 16777215 -1: 16777215 0: 0 1: 0 2: 0 8388606: 32767 8388607: 32767` [download] 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] [select]
Re^3: 3-byte representation by ikegami (Patriarch) on Oct 12, 2011 at 18:45 UTC
Thanks, a "`/256`" got accidentally dropped when I posted my code. Fixed.	[reply] [d/l]
Re^2: 3-byte representation by BrowserUk (Patriarch) on Oct 12, 2011 at 19:10 UTC
I tested my solutions before posting them. Really? Really, really? Hm? #! perl -slw use strict; sub pack24be{ substr( pack('l>', $_[0]), 1) } sub unpack24be{ unpack('l>', "$_[0]\0") >> 8 } sub pack24le{ substr( pack('l<', $_[0] ), 0, 3); } sub unpack24le{ unpack( 'l<', "\0$_[0]" ) >> 8 } print( "be: $_: ", unpack24be( pack24be( $_ ) ) ), print( "le: $_: ", unpack24le( pack24le( $_ ) ) ) for ( -8388608, -8388607, -2, -1, 0, 1, 2, 8388606, 8388607 ) __END__ C:\test>junk101 (version 2 ) be: -8388608: -2147483648 le: -8388608: -2147483648 be: -8388607: -2147483392 le: -8388607: -2147483392 be: -2: -512 le: -2: -512 be: -1: -256 le: -1: -256 be: 0: 0 le: 0: 0 be: 1: 256 le: 1: 256 be: 2: 512 le: 2: 512 be: 8388606: 2147483136 le: 8388606: 2147483136 be: 8388607: 2147483392 le: 8388607: 2147483392 C:\test>junk101 (version 3) be: -8388608: 72057594029539328 le: -8388608: 72057594029539328 be: -8388607: 72057594029539329 le: -8388607: 72057594029539329 be: -2: 72057594037927934 le: -2: 72057594037927934 be: -1: 72057594037927935 le: -1: 72057594037927935 be: 0: 0 le: 0: 0 be: 1: 1 le: 1: 1 be: 2: 2 le: 2: 2 be: 8388606: 8388606 le: 8388606: 8388606 be: 8388607: 8388607 le: 8388607: 8388607 [download] 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^2: 3-byte representation by BrowserUk (Patriarch) on Oct 12, 2011 at 19:12 UTC
Update: The >> 8 got dropped when I posted my solution. Fixed. Silently becomes Update: The /256 got dropped when I posted my solution. Fixed. Hm. "Got dropped" huh!	[reply]
Re^3: 3-byte representation by Anonymous Monk on Oct 13, 2011 at 10:48 UTC
Thank you for all your gentle answers, but if I run this: `#!/usr/bin/perl print "Content-type: text/html\n\n"; srand(); $fil="ch"; open(OUT, '>>'.$fil); for($i=1;$i<10001;$i++){ $j=int(rand(20000))+440000; $k=substr(pack('l>',$j),1); print OUT $k; } close(OUT); print "DONE !";` [download] it produces one file with a variable length, but always greater than 30000 characters (for exemple 30045) ! So I suppose something is wrong in the pack line coding...	[reply] [d/l]
Re^4: 3-byte representation by BrowserUk (Patriarch) on Oct 13, 2011 at 12:36 UTC
Add `binmode OUT` after the open. Also, you should be using a mode of '>' not '>>', unless your intention is to append to an existing file. `for($i=1;$i<10001;$i++){` is more easily and clearly written as `for my $i ( 1 .. 10000 ) {` `int(rand(20000))+440000` produces always positive integer. If you don't need signed integers, your question would have been much simpler to answer. `$k=substr(pack('l>',$j),1); print OUT $k;` Packing and writing one value at a time is hugely expensive compared to packing all 10000 values in a single pass and then writing them once. For goodness sake, use a little horizontal whitespace. Don't you find this infinitely more readable? `#!/usr/bin/perl use strict; print "Content-type: text/html\n\n"; srand(); my $fil = "ch"; open( OUT, '>', $fil ) or die $!; binmode OUT; for my $i ( 1 .. 10_000 ) { my $j = int( rand( 20_000 ) ) + 440_000; my $k = substr( pack( 'l>', $j ), 1 ); print OUT $k; } close( OUT ); print "DONE !";` [download] Remember that your source code is the equivalent of the professional chef's plated up meal. His presentation is what makes the difference between a paid for cover and a decent home cooked meal. It is both his edge and his profit margin. 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] [select]
Re^5: 3-byte representation by gerleu (Novice) on Oct 13, 2011 at 14:21 UTC
Re^6: 3-byte representation by BrowserUk (Patriarch) on Oct 13, 2011 at 15:40 UTC
Some notes below your chosen depth have not been shown here
Re^3: 3-byte representation by ikegami (Patriarch) on Oct 13, 2011 at 16:38 UTC
It was /256. Just misremembered cause I changed comps in the middle.	[reply]
Re^4: 3-byte representation by BrowserUk (Patriarch) on Oct 13, 2011 at 16:40 UTC
I actually downloaded the >>8 version before it changed.	[reply]
Re^5: 3-byte representation by ikegami (Patriarch) on Oct 13, 2011 at 17:09 UTC


Your skill will accomplish what the force of many cannot
	PerlMonks