Beefy Boxes and Bandwidth Generously Provided by pair Networks
Clear questions and runnable code
get the best and fastest answer
 
PerlMonks  

Re^3: long integer to hexadecimal conversion

by Marshall (Prior)
on Oct 01, 2009 at 13:14 UTC ( #798644=note: print w/ replies, xml ) Need Help??


in reply to Re^2: long integer to hexadecimal conversion
in thread long integer to hexadecimal conversion

The basic problem appears to be that you have a 32 bit machine and you need a bigger integer than can be represented in 32 bits.

If you have 4 bits, the biggest unsigned number that you can represent is with all 4 bits "on", is, "1111", or 15 in decimal, 2**4-1=15, or 'F'. 0123456789ABCDEF is all 16 possibilities with 4 bits.

The biggest unsigned 32 bit number is 2**32-1= 4,294,967,295.

The normal convention for representing a "signed" number is what is called 2's complement arithmetic. If you have 4 bits and have say 0001, to get "-1", you complement (reverse) all bits and then add one. 1110+1=1111. Now we come to the interpretation of whether "1111" means "15" or "-1". Basically the most significant bit becomes the "sign bit". 0111 with 4 bits is the max positive number or 2**3-1=7. 1000 is the max negative number which weirdly enough is -8.

So if you have 32 bits as signed 2's complement, you get "0111 1111 1111 1111 1111 1111 1111 1111" or 2,147,483,647 as the max positive number and -2,147,483,648 as the max negative number.

I think a Perl float uses more than 32 bits for the "mantissa". I think it maybe as many as 53 bits. I'm not sure. I think the "safest" way is to use these big int modules. The 32 bit integer to think about is 2 billion. When you get to that size integer number, things can get more complicated.

123,143,230,627 is a lot bigger than 2,147,483,647 and hence the problems.


Comment on Re^3: long integer to hexadecimal conversion

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://798644]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others cooling their heels in the Monastery: (6)
As of 2015-07-07 01:54 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    The top three priorities of my open tasks are (in descending order of likelihood to be worked on) ...









    Results (86 votes), past polls