runtime: .NET 6: System.Random - seeded implementation of .NextInt64* methods is inconsistent with .Next* methods

Description

.NET 6, 5, 3.1, and probably most .NET Frameworks:

var r1 = new Random(123);	
r1.Next().Dump(); // 2114319875
r1.Next().Dump(); // 1949518561
r1.Next().Dump(); // 1596751841
r1.Next().Dump(); // 1742987178

var r1 = new Random(123);	
r1.Next(0).Dump(); // 0 (technically does not need to consume state, but state got iterated)
r1.Next().Dump();  // 1949518561 (2nd call matches)
r1.Next().Dump();  // 1596751841 (3rd call matches)
r1.Next().Dump();  // 1742987178 (4th call matches)

var r1 = new Random(123);	
r1.Next(1).Dump(); // 0 (technically does not need to consume state, but state got iterated)
r1.Next().Dump();  // 1949518561 (2nd call matches)
r1.Next().Dump();  // 1596751841 (3rd call matches)
r1.Next().Dump();  // 1742987178 (4th call matches)

var r1 = new Random(123);
r1.Next((1 << 30) + 1).Dump(); // 1057159938 (iterates state only once)
r1.Next().Dump();              // 1949518561 (2nd call matches)
r1.Next().Dump();              // 1596751841 (3rd call matches)
r1.Next().Dump();              // 1742987178 (4th call matches)

.NET 6:

var r2 = new Random(123);
r2.NextInt64().Dump(); // 5751341171501756545
r2.NextInt64().Dump(); // 1468073721509004893
r2.NextInt64().Dump(); // 4492647383573077195
r2.NextInt64().Dump(); // 7443599010373778036

var r2 = new Random(123);
r2.NextInt64(0).Dump(); // 0 (state not consumed)
r2.NextInt64().Dump();  // 5751341171501756545 (different - 1st state consumption)
r2.NextInt64().Dump();  // 1468073721509004893 (different - 2nd state consumption)
r2.NextInt64().Dump();  // 4492647383573077195 (different - 3rd state consumption)

var r2 = new Random(123);
r2.NextInt64(1).Dump(); // 0 (state not consumed)
r2.NextInt64().Dump();  // 5751341171501756545 (different - 1st state consumption)
r2.NextInt64().Dump();  // 1468073721509004893 (different - 2nd state consumption)
r2.NextInt64().Dump();  // 4492647383573077195 (different - 3rd state consumption)

var r2 = new Random(123);
r2.NextInt64((1 << 62) + 1).Dump(); // 341812549 (state is consumed twice) 
r2.NextInt64().Dump();              // 4492647383573077195 (matches 4th result above)
r2.NextInt64().Dump();              // 7443599010373778036
r2.NextInt64().Dump();              // 1003052373149355376

Conclusions

Legacy seeded System.Random consumes state in stable fixed consumptions per API-call, regardless of parameters passed into API (as long as they are valid).

New .NextInt64* methods deviate from this expected (but not documented) behavior, and consume state in variable number of consumptions per API-call, depending on the input values.

Legacy seeded System.Random has always had the (undocumented) design of state-rotations being a function of the API calls only, but not the specific parameters. New .NextInt64* methods should have the same behavior to ensure consistency and reproducibility.

P.S.

System.Random test-suite is missing these scenarios…

@stephentoub @jkotas