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NAME ==== Raku port of Perl's math built-ins SYNOPSIS ======== use P5math; # exports abs cos crypt exp int log rand sin sqrt DESCRIPTION =========== This module tries to mimic the behaviour of Perl's `abs`, `cos`, `crypt`, `exp`, `int`, `log`, `rand`, `sin` and `sqrt` builtins as closely as possible in the Raku Programming Language.. 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($word = <STDIN>); print "\n"; system "stty echo"; if (crypt($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 PORTING CAVEATS =============== Can not use int() ----------------- As of this writing (2020.10), 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 Raku. crypt() not supported on all platforms -------------------------------------- The `crypt` function will return `Nil` if it is not supported by the OS. $_ no longer accessible from caller's scope ------------------------------------------- In future language versions of Raku, it will become impossible to access the `$_` variable of the caller's scope, because it will not have been marked as a dynamic variable. So please consider changing: cos; to either: cos($_); or, using the subroutine as a method syntax, with the prefix `.` shortcut to use that scope's `$_` as the invocant: .&cos; AUTHOR ====== Elizabeth Mattijsen <[email protected]> Source can be located at: https://github.com/lizmat/P5math . Comments and Pull Requests are welcome. COPYRIGHT AND LICENSE ===================== Copyright 2018-2020 Elizabeth Mattijsen Re-imagined from Perl 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.