# NAME

Math::Random::PCG32 - minimal PCG random number generator

# SYNOPSIS

```
use Math::Random::PCG32;
# probably want a better seed, see Math::Random::Secure
# a game by contrast could want the seed given by YYYYMMDD
my $rng = Math::Random::PCG32->new( 42, 54 );
$rng->coinflip; # 0,1
$rng->decay( 2147483648, 1, 20 ); # 50% odds decay from 1 out to 20
# (results closer to 1 than 20)
$rng->irand; # 32-bit unsigned int
$rng->irand_in( 1, 100 ); # 1..100 result (biased)
$rng->rand; # float [0..1) (biased)
$rng->rand(10); # previous multiplied by ...
$rng->rand_elm( \@a ); # random element of array (biased)
$rng->rand_from( \@a ); # splice out a random element "
$rng->rand_idx( \@a ); # random index of array "
$rng->roll( 3, 6 ); # 3d6 (biased)
```

# DESCRIPTION

This module includes a minimal PCG (Permuted Congruential Generator) for random numbers

and some utility routines for PCG (Procedural Content Generation).

## A RANDOM BENCHMARK

This pits the (very bad) core `rand`

function against the **rand** methods from Math::Random::ISAAC, Math::Random::MTwist, Math::Random::Xorshift, and this module for `cmpthese( -5, ...`

via the Benchmark module on my somehow still functional 2009 macbook.

```
Rate isacc xorsh mtwist pcg rand
isacc 214269/s -- -92% -96% -96% -99%
xorsh 2661857/s 1142% -- -47% -52% -88%
mtwist 5030175/s 2248% 89% -- -9% -78%
pcg 5518583/s 2476% 107% 10% -- -75%
rand 22447322/s 10376% 743% 346% 307% --
```

# METHODS

Various methods may croak if invalid input is detected. Use **new** to obtain an object and then call the others using that. Note that many of these are biased, as this module favors speed and is expected to deal only with small numbers.

**new***initstate**initseq*-
Makes a new object. No peeking! The two seed values must be 64-bit unsigned integers. These could be read off of

`/dev/urandom`

, e.g.`use Fcntl; my $raw; sysopen( my $fh, "/dev/urandom", O_RDONLY ) or die ...; ... = sysread $fh, $raw, 8; my $seed = unpack "Q", $raw;`

or for a game one might use values from Time::HiRes or provided by the user.

*initstate*and*initseq*are documented at: **coinflip**-
Returns

`0`

or`1`

.*Since version 0.17.* **decay***odds**min**max*-
Increments

*min*while successive random values are less than*odds*ending should a random value fail or*max*be reached.*odds*is treated as a`uint32_t`

value (as are*min*and*max*), so 50% odds of decay would be`2147483648`

. Returns the value*min*is incremented to. **irand**-
Returns a random number from an object constructed by

**new**. The return value is a 32-bit unsigned integer.Used to be called

**rand**in older versions of the module. **irand64**-
Returns a 64-bit unsigned integer, possibly by sticking the result of two calls to the RNG together.

**irand_in***min**max*-
Returns a random integer in the range of

*min*to*max*, inclusive. **irand_way***x1**y1**x2**y2*-
Returns a new point as a list that will bring the first point (given by

*x1*,*y1*) towards the second point or`undef`

if the points are the same.Overflows are not checked for; do not use points that will result in deltas or magnitudes greater than can be handled without overflow by 32-bit values.

**rand**[*factor*]-
Returns a floating point value in the range 0.0 <= n < 1.0, or in some other range if a number is given as a

*factor*. **rand_elm***array-reference*-
Returns a random element from the given array, or

`undef`

if the array is empty (or if that is what the array element contained). The reference is not modified. **rand_from***array-reference*-
Like

**rand_elm**but cuts the element out of the array reference before returning it. Pretty similar to`splice`

with a random index:`$rng->rand_from(\@seed); splice @seed, rand @seed, 1;`

*Since version 0.17.* **rand_idx***array-reference*-
Returns a random index from the given array, or

`undef`

if the array is empty. **roll***count**sides*-
Sums the result of rolling the given number of dice.

*Since version 0.17.*Prior to that was called**dice**. Prior to version 0.10 did not exist. **sample***count**array-reference*-
Returns

*count*random elements from*array-reference*as an array reference, or an empty array reference if the*count*is zero or the length of the*array-reference*is zero. The elements are returned in the same order as they appear in the*array-reference*.*Since version 0.23.*

# CAVEATS

This module MUST NOT be used for anything cryptographic or security related. It probably should not be used for any analysis that needs non-biased pseudo random numbers.

Various routines are subject to various forms of modulo bias so will become increasingly unsound as the values used approach `UINT32_MAX`

. If modulo bias is a concern this module is **not** what you need. More reading:

https://www.pcg-random.org/posts/bounded-rands.html

This module does use `%`

(which is biased) in various routines; there are apparently faster methods (or ones more suitable for larger inputs) though benchmarking

```
uint32_t byinteger(uint32_t max) {
uint32_t x = rand();
uint64_t m = (uint64_t) x * (uint64_t) max;
return m >> 32;
}
```

against

` uint32_t bymodulus(uint32_t max) { return rand() % max; }`

did not show any notable speed gain for me (though perhaps my benchmark was flawed, or compiler too old? YMMV).

# BUGS

## Reporting Bugs

Patches might best be applied towards:

https://github.com/thrig/Math-Random-PCG32

## Known Issues

Probably needs a modern compiler for the `stdint`

types. Untested on older versions of Perl. Untested (by me) on 32-bit versions of Perl; `use64bitint=define`

is now required.

Various tradeoffs have been made to always favor speed over safety: modulo bias is ignored and some methods have integer overflow issues. Using numbers well below `INT32_MAX`

should avoid these issues.

# SEE ALSO

https://www.pcg-random.org/using-pcg-c-basic.html

https://github.com/imneme/pcg-c-basic

Math::Random::Secure for good seed choice.

http://xoshiro.di.unimi.it for a different PRNG and tips on compiler flags for use during benchmarks.

```
"though I must say, those PRNG writers, it feels like they are in a
small scale war with each other at times"
-- random chat comment
```

# AUTHOR

thrig - Jeremy Mates (cpan:JMATES) `<jeremy.mates at gmail.com>`

# COPYRIGHT AND LICENSE

Perl module copyright (C) 2018 by Jeremy Mates

Code under src/ directory (c) 2014 M.E. O'Neill / pcg-random.org

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

` L<http://www.apache.org/licenses/LICENSE-2.0>`

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.