Fix unnecessary modulo operations in Index1D.h

[NaNExist]

Description

This PR replaces unnecessary modulo operations with multiplication and subtraction.

Motivation and context

I was browsing through the project code and realised that this was a change that would improve performance.

How has this been tested?

Local compilation passes fine.

Change log

* Fix unnecessary modulo operations in Index1D.h

Checklist:

• I have reviewed the Contributor Guidelines.
• I agree with the terms of the HOOMD-blue Contributor Agreement.
• My name is on the list of contributors (sphinx-doc/credits.rst) in the pull request source branch.

[joaander]

Thanks, I appreciate the effort. However, getPair() is dead code. It is called by only one code path that has not bee used for many years. I plan to remove it in the next release (#1664):

hoomd-blue/hoomd/CellListGPU.cu

Line 315 in ec0b84c

uint2 p = cli.getPair(idx);

[joaander]

#1936 removes the code that unnecessarily invokes the modulus.