laziness, impatience, and hubris PerlMonks

### comment on

 Need Help??

Probably the key improvement here is the use of hexadecimal notation:   0xffffffff instead of the corresponding, “magic” decimal.   As long as you are very careful to use unsigned arithmetic and specify bitmasks that are no larger than the integer-size you know that you are using, code like this ought to be transportable.   (It might not be readable, heh, but it ought to be int-length agnostic.)

I would almost edit my comment to say, don’t use “arithmetic” at all when you are bit-twiddling, as in code like this:

```\$num = \$num - 4294967296 if \$num > 4294967295;
\$num = \$num + 4294967296 if \$num < -2147483648;
That’s nasty...   And I recognize at least one of those numbers, -2147483648, as an old, familiar 32-bit friend.   I also detect the presence of signed arithmetic, dependent upon the thirty-first bit being the sign-bit.   I suggest that this code should be rewritten to use bit-masking operators ... and to do so, perhaps, in a very specific way, as follows:

If you want to mash-off, say, all but the rightmost 31 bits of an integer quantity, you should take:   qty := qty and ( not 0x7fffffff );.   (I am not using Perl notation here, for clarity.)   The subexpression, (not 0x7fffffff), will evaluate to an int in which all bits are 1 except for the rightmost 31 bits, and it will do so correctly no matter what the sizeof(int) may be.

So, I suggest that you need to go through code like this (fortunately, it is a small piece of code), work out what it is doing and then rewrite it.   Construct a very thorough set of Test::More cases that you can run on both a 32-bit and a 64-bit system to prove that your rewrite is thoroughly correct.

In reply to Re: emulate 32-bit on perl 64 by sundialsvc4
in thread emulate 32-bit on perl 64 by loofort

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or or How to display code and escape characters are good places to start.

Create A New User
Domain Nodelet?
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others chanting in the Monastery: (3)
As of 2022-01-25 16:21 GMT
Sections?
Information?
Find Nodes?
Leftovers?
Voting Booth?
In 2022, my preferred method to securely store passwords is:

Results (67 votes). Check out past polls.

Notices?