GitLab

* Began vectorizing CustomNonbondedForce

* Refactored CpuCustomNonbondedForce to support multiple vector sizes

* AVX implementation of CpuCustomNonbondedForce

* Fixed compilation errors

* Began implementing vectorization of Lepton expressions

* Tests for vector expressions

* Implemented CompiledVectorExpression for x86

* Bug fix

* Optimized select() on ARM

* Optimized select() on x86

* CompiledVectorExpression supports AVX

* Bug fix

* Updated docs

* Use VEX encoded instructions for CompiledExpression

* Optimized min() and max() on x86

* Optimized min() and max() on ARM

* Fixed compilation error

* Upgrade AsmJit

* Optimized computing powers in CompiledExpression

* Fixed compilation error

* Attempt at fixing compilation error

* Upgraded to new version of asmjit

* JIT compilation for ARM

* Updated CMake script

* Simplified derivatives of min() and max()

* Fixed compilation error in kernel

* Optimizations to Lepton

* More optimizations to Lepton

See https://github.com/lammps/lammps/pull/1992

Lepton::ParsedExpression::getConstantValue() used to return NaN to indicate non-constant
expressions. This can break with -ffast-math optimization where NaN comparisons are
not defined.

This patch defines bool isConstant() to test whether an expression is constant before
calling getConstantValue(). getConstantValue() now throws an exception if called on a
non-constant expression.

The pragma to ignore 4251 already existed in windowsIncludes.h, and it works
when compiling lepton itself. However, when clients use lepton, they get this
warning. I think this is why @sherm1 put the define as shown here:
https://github.com/simbody/simbody/blob/master/SimTKcommon/include/SimTKcommon/internal/common.h#L168
 (whether or not the shared library is being built or used).

Clang had been generating the following warning:

```
ParsedExpression.cpp:123:13:
warning:
      30 enumeration values not handled in switch: 'CONSTANT', 'VARIABLE',
      'CUSTOM'...
            [-Wswitch]
                switch (node.getOperation().getId()) {
                                ^
                                1 warning generated.
```

To get rid of this warning, I added a default case, which does nothing.