Question 1

How fast is fastmod compared to regular division?

Accepted Answer

fastmod is specifically faster for constant divisors, with benchmarks on Intel Skylake showing it outperforms compiler optimizations. However, for variable divisors, the need to precompute multipliers can offset performance gains.

Question 2

How to use fastmod with signed integers?

Accepted Answer

For signed operations, use computeM_s32 with the absolute value of the divisor and avoid divisors like -1 or INT32_MIN. The README provides an example showing how to compute mod for negative numbers using fastmod_s32.

Question 3

Is fastmod compatible with my compiler?

Accepted Answer

fastmod supports Clang, GCC, and Visual Studio, and requires C++11 compatibility. Check the README for build instructions; for instance, benchmarks for 64-bit operations are not supported on Visual Studio.

Question 4

What are the benchmarks for fastmod performance?

Accepted Answer

Benchmarks included in the docs show performance gains on Intel Skylake with Clang. You can run your own benchmarks using the provided make commands, but note that 64-bit benchmarks are experimental and not available on all platforms.

Question 5

fastmod vs libdivide: which is better?

Accepted Answer

fastmod focuses on 32-bit operations with constant divisors and is header-only, while libdivide offers similar optimizations but may differ in features. Choose based on your specific needs—fastmod is backed by research on direct computation, but libdivide might be more mature for certain use cases.

Question 6

How to integrate fastmod into a CMake project?

Accepted Answer

Since it's header-only, just include fastmod.h in your source files. For building and testing, use the CMake commands from the README: 'cmake -B build' and 'cmake --build build', which set up the project and run tests.

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