Scalar::Number(3pm)

NAME

Scalar::Number - numeric aspects of scalars

SYNOPSIS

use Scalar::Number qw(scalar_num_part);

$num = scalar_num_part($scalar);

use Scalar::Number qw(sclnum_is_natint sclnum_is_float);

if(sclnum_is_natint($value)) { ...
if(sclnum_is_float($value)) { ...

use Scalar::Number qw(sclnum_val_cmp sclnum_id_cmp);

@sorted_nums = sort { sclnum_val_cmp($a, $b) } @floats;
@sorted_nums = sort { sclnum_id_cmp($a, $b) } @floats;

DESCRIPTION

This module is about the numeric part of plain (string) Perl scalars.
A scalar has a numeric value, which may be expressed in either the
native integer type or the native floating point type. Many values are expressible both ways, in which case the exact representation is
insignificant. To fully understand Perl arithmetic it is necessary to know about both of these representations, and the differing behaviours of numbers according to which way they are expressible.

This module provides functions to extract the numeric part of a scalar, classify a number by expressibility, and compare numbers across
representations.

This module is implemented in XS, with a pure Perl backup version for
systems that can't handle XS.

FUNCTIONS

Each "sclnum_" function takes one or more scalar numeric arguments to
operate on. These arguments must be numeric; giving non-numeric
arguments will cause mayhem. See "is_number" in Params::Classify for a way to check for numericness. Only the numeric value of the scalar is used; the string value is completely ignored, so dualvars are not a
problem.
Decomposition: scalar_num_part(SCALAR)
Extracts the numeric value of SCALAR, and returns it as a pure
numeric scalar. The argument is permitted to be any scalar.

Every scalar has both a string value and a numeric value. In pure string scalars, those resulting from string literals or string
operations, the numeric value is determined from the string value. In pure numeric scalars, those resulting from numeric literals or
numeric operations, the string value is determined from the numeric value. In the general case, however, a plain scalar's string and
numeric values may be set independently, which is known as a
dualvar. Non-plain scalars, principally references, determine
their string and numeric values in other ways, and in particular a reference to a blessed object can stringify and numerify however
the class wishes.

This function does not warn if given an ostensibly non-numeric
argument, because the whole point of it is to extract the numeric
value of scalars that are not pure numeric.
Classification: sclnum_is_natint(VALUE)
Returns a truth value indicating whether the provided VALUE can be represented in the native integer data type. If the floating point type includes signed zeroes then they do not qualify; the only zero representable in the integer type is unsigned.; sclnum_is_float(VALUE)
Returns a truth value indicating whether the provided VALUE can be represented in the native floating point data type. If the
floating point type includes signed zeroes then an unsigned zero
(from the native integer type) does not qualify.
Comparison: sclnum_val_cmp(A, B)
Numerically compares the values A and B. Integer and floating
point values are compared correctly with each other, even if there is no available format in which both values can be accurately
represented. Returns -1, 0, +1, or undef, indicating whether A is less than, equal to, greater than, or not comparable with B. The
"not comparable" situation arises if either value is a floating
point NaN (not-a-number). All flavours of zero compare equal.

This is very similar to Perl's built-in <=> operator. The only
difference is the capability to compare integer against floating
point (where neither can be represented exactly in the other's
format). <=> performs such comparisons in floating point, losing
accuracy of the integer value.; sclnum_id_cmp(A, B)
This is a comparison function supplying a total ordering of scalar numeric values. Returns -1, 0, or +1, indicating whether A is to
be sorted before, the same as, or after B.

The ordering is of the identities of numeric values, not their
numerical values. If floating point zeroes are signed, then the
three types (positive, negative, and unsigned) are considered to be distinct. NaNs compare equal to each other, but different from all numeric values. The exact ordering provided is mostly numerical
order: NaNs come first, followed by negative infinity, then
negative finite values, then negative zero, then unsigned zero,
then positive zero, then positive finite values, then positive
infinity.

In addition to sorting, this function can be useful to check for a zero of a particular sign.

BUGS

In Perl 5.6, if configured with a wider-than-usual native integer type such that there are native integers that can't be represented exactly
in the native floating point type, it is not always possible to
distinguish between integer and floating point values in pure Perl
code. In order to get the full benefit of either type, one is expected (by the numeric semantics) to know in advance which of them one is
using. The pure Perl version of this module can't operate on such a
system, but the XS version works fine. This problem is resolved by
Perl 5.8's new numeric semantics.

AUTHOR

Andrew Main (Zefram) <zefram@fysh.org>

COPYRIGHT

LICENSE

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

docs.sk

comprehensive documentation repository

See also