[Add] GetRandom(MaxValue) to StdLib Contract

[cschuchardt88]

Description

Adds two new methods to StdLib contract. Still uses syscall GetRandom for getting ranges. Updated GetRandom syscall to have 256 bit integer.

Methods

// A 256-bit unsigned integer that is greater than or equal to 0 and less than MaxValue.
BigInteger GetRandom(BigInteger maxValue); 

Fixes #3817

Type of change

• Optimization (the change is only an optimization)
• Style (the change is only a code style for better maintenance or standard purpose)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Locally Unit Tested

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[cschuchardt88]

@shargon maybe you help me with

/_/tests/Neo.UnitTests/SmartContract/Native/UT_NativeContract.cs(256): error test failed: TestGenesisNativeState (32ms): Assert.AreEqual failed. Expected:

and setting up hardfork.

[shargon]

@shargon maybe you help me with

/_/tests/Neo.UnitTests/SmartContract/Native/UT_NativeContract.cs(256): error test failed: TestGenesisNativeState (32ms): Assert.AreEqual failed. Expected:

and setting up hardfork.

I will do it

[Wi1l-B0t]

The engine.GetRandom() returns 128-bit filled buffers.
So there is another idea:

1. If the maxValue is less than or equal to 128bit, generate a 128-bit random number(between [0, maxValue)) once. Like this: https://cs.opensource.google/go/go/+/master:src/math/rand/rand.go;l=120
2. If the maxValue is greater than 128bit, generate a random number(between [0, maxValue >> 128bit), i.e. rand1) once, and engine.GetRandom() once, the result is engine.GetRandom() & (rand1 << 128).

The operation maxValue * is not needed in this way.

[cschuchardt88]

The bigger the number (and these numbers can be huge, if you look at the tests) the longer it takes to loop. So in this case (so it doesnt take long time) we only want to take no bigger than maxValue bits. That could be a number of 10 or Pow(100, 100). In other words its faster this way or else you run out of gas or takes to long. Also can be up to 256-bits.

[roman-khimov]

Still need some time, likely can be simplified a bit.

[roman-khimov]

Not sure what this buys you. Either we have pseudorandom bits from murmur128 and trust it to have them or this doesn't change much.

[cschuchardt88]

Still need some time, likely can be simplified a bit.

@roman-khimov

[shargon]

random_times is not defined

[cschuchardt88]

where did it go?

[cschuchardt88]

@roman-khimov when are you going to review this?