Hello Monks,

The business values I operated are floats; meanwhile the module I use to them in shared memory uses integers, that also guarantees the atomicity of writing int-values in shared memory.

Is there any way to pack (not convert) float to integer, without loosing precision? Way# 1

my $packed_integer = int($float * 1_000_000);
my $unpacked_float = $packed_integer / 1_000_000;
[download]

Obviously, I loose precision here. In C I can do to manipulation with pointers, to get the result I like:

assert(sizeof(int) >= sizeof(float));
 
float f = ...;
int *i_ptr = (int*)&f;
int i = *int;
[download]

Then I've found can do something like that via pack/upack build-ins in Perl:

my $v = 1/3;
my $v2 = unpack("F", pack("j", unpack("j", pack("F", $v))));
print ("v = $v\nv = $v2\n");

# v = 0.333333333333333
# v = 0.333333333333333
[download]

Seems fine.

• Is there any hidden problem with pack/unpack here?
• How to emulate C's assert in perl, i.e. how to get sizeof:

  die("float cannot be packed into integer") 
    unless ($int_size >= $float_size);
  [download]

  ?
• May be there is already some module that does that? If there is no, does it worth to make a small module with pack + assert as above?

Thanks!

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.