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NAME
====
P5math - Port of Perl 5's math built-ins to Perl 6
SYNOPSIS
========
use P5math; # exports abs cos crypt exp int log rand sin sqrt
DESCRIPTION
===========
This module tries to mimic the behaviour of the `abs`, `cos`, `crypt`, `exp`, `int`, `log`, `rand`, `sin` and `sqrt` functions of Perl 5 as closely as possible.
PORTING CAVEATS
===============
As of this writing (2018.05), it is **not** possible to actually use `int` in your code because of code generation issue caused by the fact that `int` is a built-in native type in Perl 6.
Other functions may not be callable without actually specifying (no) parameters.
ORIGINAL PERL 5 DOCUMENTATION
=============================
abs VALUE
abs Returns the absolute value of its argument. If VALUE is omitted,
uses $_.
cos EXPR
cos Returns the cosine of EXPR (expressed in radians). If EXPR is
omitted, takes the cosine of $_.
For the inverse cosine operation, you may use the
"Math::Trig::acos()" function, or use this relation:
sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) }
crypt PLAINTEXT,SALT
Creates a digest string exactly like the crypt(3) function in the
C library (assuming that you actually have a version there that
has not been extirpated as a potential munition).
crypt() is a one-way hash function. The PLAINTEXT and SALT are
turned into a short string, called a digest, which is returned.
The same PLAINTEXT and SALT will always return the same string,
but there is no (known) way to get the original PLAINTEXT from the
hash. Small changes in the PLAINTEXT or SALT will result in large
changes in the digest.
There is no decrypt function. This function isn't all that useful
for cryptography (for that, look for Crypt modules on your nearby
CPAN mirror) and the name "crypt" is a bit of a misnomer. Instead
it is primarily used to check if two pieces of text are the same
without having to transmit or store the text itself. An example is
checking if a correct password is given. The digest of the
password is stored, not the password itself. The user types in a
password that is crypt()'d with the same salt as the stored
digest. If the two digests match, the password is correct.
When verifying an existing digest string you should use the digest
as the salt (like "crypt($plain, $digest) eq $digest"). The SALT
used to create the digest is visible as part of the digest. This
ensures crypt() will hash the new string with the same salt as the
digest. This allows your code to work with the standard crypt and
with more exotic implementations. In other words, assume nothing
about the returned string itself nor about how many bytes of SALT
may matter.
Traditionally the result is a string of 13 bytes: two first bytes
of the salt, followed by 11 bytes from the set "[./0-9A-Za-z]",
and only the first eight bytes of PLAINTEXT mattered. But
alternative hashing schemes (like MD5), higher level security
schemes (like C2), and implementations on non-Unix platforms may
produce different strings.
When choosing a new salt create a random two character string
whose characters come from the set "[./0-9A-Za-z]" (like "join '',
('.', '/', 0..9, 'A'..'Z', 'a'..'z')[rand 64, rand 64]"). This set
of characters is just a recommendation; the characters allowed in
the salt depend solely on your system's crypt library, and Perl
can't restrict what salts "crypt()" accepts.
Here's an example that makes sure that whoever runs this program
knows their password:
$pwd = (getpwuid($<))[1];
system "stty -echo";
print "Password: ";
chomp($word = );
print "\n";
system "stty echo";
if (crypt($word, $pwd) ne $pwd) {
die "Sorry...\n";
} else {
print "ok\n";
}
Of course, typing in your own password to whoever asks you for it
is unwise.
The crypt function is unsuitable for hashing large quantities of
data, not least of all because you can't get the information back.
Look at the Digest module for more robust algorithms.
If using crypt() on a Unicode string (which potentially has
characters with codepoints above 255), Perl tries to make sense of
the situation by trying to downgrade (a copy of) the string back
to an eight-bit byte string before calling crypt() (on that copy).
If that works, good. If not, crypt() dies with "Wide character in
crypt".
Portability issues: "crypt" in perlport.
exp EXPR
exp Returns me (the natural logarithm base) to the power of EXPR. If
EXPR is omitted, gives "exp($_)".
int EXPR
int Returns the integer portion of EXPR. If EXPR is omitted, uses $_.
You should not use this function for rounding: one because it
truncates towards 0, and two because machine representations of
floating-point numbers can sometimes produce counterintuitive
results. For example, "int(-6.725/0.025)" produces -268 rather
than the correct -269; that's because it's really more like
-268.99999999999994315658 instead. Usually, the "sprintf",
"printf", or the "POSIX::floor" and "POSIX::ceil" functions will
serve you better than will int().
log EXPR
log Returns the natural logarithm (base e) of EXPR. If EXPR is
omitted, returns the log of $_. To get the log of another base,
use basic algebra: The base-N log of a number is equal to the
natural log of that number divided by the natural log of N. For
example:
sub log10 {
my $n = shift;
return log($n)/log(10);
}
See also "exp" for the inverse operation.
rand EXPR
rand Returns a random fractional number greater than or equal to 0 and
less than the value of EXPR. (EXPR should be positive.) If EXPR is
omitted, the value 1 is used. Currently EXPR with the value 0 is
also special-cased as 1 (this was undocumented before Perl 5.8.0
and is subject to change in future versions of Perl).
Automatically calls "srand" unless "srand" has already been
called. See also "srand".
Apply "int()" to the value returned by "rand()" if you want random
integers instead of random fractional numbers. For example,
int(rand(10))
returns a random integer between 0 and 9, inclusive.
(Note: If your rand function consistently returns numbers that are
too large or too small, then your version of Perl was probably
compiled with the wrong number of RANDBITS.)
"rand()" is not cryptographically secure. You should not rely on
it in security-sensitive situations. As of this writing, a number
of third-party CPAN modules offer random number generators
intended by their authors to be cryptographically secure,
including: Data::Entropy, Crypt::Random, Math::Random::Secure, and
Math::TrulyRandom.
sin EXPR
sin Returns the sine of EXPR (expressed in radians). If EXPR is
omitted, returns sine of $_.
For the inverse sine operation, you may use the "Math::Trig::asin"
function, or use this relation:
sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) }
sqrt EXPR
sqrt Return the positive square root of EXPR. If EXPR is omitted, uses
$_. Works only for non-negative operands unless you've loaded the
"Math::Complex" module.
use Math::Complex;
print sqrt(-4); # prints 2i
AUTHOR
======
Elizabeth Mattijsen
Source can be located at: https://github.com/lizmat/P5math . Comments and Pull Requests are welcome.
COPYRIGHT AND LICENSE
=====================
Copyright 2018 Elizabeth Mattijsen
Re-imagined from Perl 5 as part of the CPAN Butterfly Plan.
This library is free software; you can redistribute it and/or modify it under the Artistic License 2.0.