feat(examples): Add a useful set of high quality pseudo-random number generators

[wyhaines]

I ported a number of my pseudo-random number generator implementations from Ruby to gno while traveling to the retreat last weekend as an exercise in expanding my comfort level with gno code while contributing code that others may find interesting or useful.

I added two xorshift generators, xorshift64* and xorshiftr128+. These are both many times faster than the PCG generator that is the gno default, and produce high quality randomness with great statistical qualities. In addition to these, I added both the 32-bit ISAAC implementation (with an added function to return 64 bit values), and the 64-bit ISAAC implementation. ISAAC is a stellar pseudo-random number generator. Both implementations are significantly faster than PCG (though not near so fast as the xorshift algorithms), while producing extremely high quality, cryptographically secure randomness that can not be differentiated from real randomness.

All of these were built to be compatible with the standard Rand() implementation. This means that any of these can be used as a drop-in replacement for the default PCG algorithm:

source = isaac.New()
prng := rand.New(source)

All of these leverage the gno.land/p/demo/entropy package to assist with seeding if no seed is provided. In the case of the ISAAC algorithms, they require 256 uint values for their seed, so they leverage a combination of entropy and xorshiftr128+ to generate any missing numbers in the provided seed.

I also added a function to entropy to return uint64, to facilitate using it for seeding.

I added tests to entropy, and wrote tests for the other generators, as well.

There are a few other things that ended up in this PR. In order to make some fact based assertions about the performance of these generators, I included some code that can be ran via gno run -expr. i.e. gno run -expr 'averageISAAC()' isaac.gno that can be used to get some benchmarks and some very simple self-statistical-analysis on the results, and when I did so, I discovered that the current ufmt.Sprintf implementation didn't support %f output. So, I added that to it's capabilities, which, in turn, required adding FormatFloat to the strconv.gno/strconv.go implementation in the standard library. I added a test to cover this.

I also noticed that there is a test in tm2/pkg/p2p that is failing on both master and my branch, so I took what may be a naive approach to fixing it.

Contributors' checklist...

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 60.97%. Comparing base (a2b4d4b) to head (2ce7d3d).
Report is 6 commits behind head on master.

Files with missing lines	Patch %	Lines
gnovm/stdlibs/strconv/strconv.go	83.33%	1 Missing ⚠️
tm2/pkg/p2p/switch.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2868      +/-   ##
==========================================
+ Coverage   60.95%   60.97%   +0.01%     
==========================================
  Files         564      564              
  Lines       75273    75298      +25     
==========================================
+ Hits        45885    45910      +25     
- Misses      26018    26019       +1     
+ Partials     3370     3369       -1     

Flag	Coverage Δ
contribs/gnodev	61.46% <ø> (ø)
gno.land	67.92% <ø> (ø)
gnovm	65.81% <96.55%> (+0.03%)	⬆️
tm2	61.99% <0.00%> (-0.08%)	⬇️

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