String adding

tim0304 has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: String adding by Limbic~Region (Chancellor) on Nov 11, 2005 at 19:10 UTC
tim0304, I think this does what you want. `my $hex = '0FB0306F207265616420746869733F'; my $sum; $sum += hex($_) for unpack('A2' x (length($hex) / 2), $hex); print $sum;` [download] Cheers - L~R	[reply] [d/l]
Re^2: String adding by Roy Johnson (Monsignor) on Nov 11, 2005 at 19:20 UTC
`$sum += hex($_) for $hex=~/../g;` [download] Is a bit less intimidating, IMO. Caution: Contents may have been coded under pressure.	[reply] [d/l]
Re^2: String adding by ikegami (Patriarch) on Nov 11, 2005 at 19:14 UTC
and save the result in Hex* to a variable.* Add: `$sum_as_hex = sprintf('%X', $sum);` [download]	[reply] [d/l]
Re^2: String adding by sauoq (Abbot) on Nov 11, 2005 at 20:01 UTC
`unpack('A2' x (length($hex) / 2), $hex);` [download] I'd rewrite that as `unpack('(A2)*', $hex);` [download] -sauoq "My two cents aren't worth a dime.";	[reply] [d/l] [select]
Re^3: String adding by ikegami (Patriarch) on Nov 11, 2005 at 21:14 UTC
That fails in 5.6.x. The parens were added to `pack` in 5.8.0	[reply] [d/l]
Re: String adding by BrowserUk (Patriarch) on Nov 11, 2005 at 19:39 UTC
Sounds like your calculating a checksum? `perl> $hex = '0FB0306F207265616420746869733F';; perl> print unpack '%32C', pack 'H', $hex;; 1329` [download] And if you need the result in hex `perl> print unpack 'H', pack 'N', unpack '%32C', pack 'H*', $hex;; 00000531` [download] Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal? "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l] [select]
Re: String adding by ikegami (Patriarch) on Nov 11, 2005 at 19:16 UTC
Alternative: `use List::Util qw( sum ); my $hex = '0FB0306F207265616420746869733F'; my $sum = sum map hex, $hex =~ /../g; my $sum_as_hex = sprintf '%X', $sum;` [download]	[reply] [d/l] [select]
Re: String adding by sgifford (Prior) on Nov 11, 2005 at 19:24 UTC
You may want to look at using something like bignum with one of the approaches ~~below~~ above. With numbers this large, I believe Perl will convert them into floating-point numbers, and so will lose accuracy. The alternative is to handle the carry-out parts yourself, but that's hard, and is essentially what `bignum` does anyways. Update: Oops, I misread the question; I thought you were adding two strings of hex digits, not adding up the hex pairs in one string. Thanks to ikegami and Roy Johnson for showing me the error of my ways. :)	[reply] [d/l]
Re^2: String adding by ikegami (Patriarch) on Nov 11, 2005 at 19:38 UTC
bignum isn't needed. The example only requires 11 bits, for example. Perl uses doubles which have 52 bits of precision. The above algorithms can safely handle strings (((2^52)-1)/((2^8)-1))2 = 17,661,175,009,296 chararacters long. Using just ints on a 32 bit system, the above algorithms can safely handle strings (((2^32)-1)/((2^8)-1))2 = 16,843,008 chararacters long.	[reply]
Re: String adding by l.frankline (Hermit) on Nov 12, 2005 at 12:21 UTC
Hi Tim, You can also go with this... `$_ = '0FB0306F207265616420746869733F';` `$_ =~s#([A-F0-9]{2})#$1+#g;` `$_=~s#\+$##;` `print hex($_);` regards Franklin Don't put off till tomorrow, what you can do today.	[reply] [d/l] [select]