Jonas Hahnfeld - Doctoral Student at CERN

Jonas Hahnfeld

Doctoral Student at CERN

France

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Summary

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Jonas Hahnfeld is a doctoral student and seasoned systems engineer with 13 years of experience focused on high-performance computing, compiler internals, and scientific simulation. Based at CERN in France, he develops parallel RNTuple writing and has a track record optimizing core components in projects like ROOT, Cling and LLVM, contributing to widely used open-source compilers and tools. His work spans robust backend engineering—fixing memory leaks, improving JIT exception handling, and optimizing random number generators—to performance tuning for GPUs and physics simulations in Geant4. Jonas combines deep low-level C++ expertise with practical systems engineering, evidenced by contributions to the Cling C++ interpreter and LLVM’s OpenMP/device toolchains. Not obviously, he also bridges academic research and production code by prototyping GPU Monte Carlo simulations and building portable, high-performance algorithms that endure in large scientific codebases.

13 years of coding experience

Computer Science, Computer Science at Goethe University Frankfurt

Master of Science - MS, Informatik, Master of Science - MS, Informatik at RWTH Aachen University

Bachelor of Science (B.Sc.), Scientific Programming, Bachelor of Science (B.Sc.), Scientific Programming at Fachhochschule Aachen

German, English, French

Stackoverflow

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Github Skills (47)

algorithm10

simulation10

debugging10

code-optimization10

algorithms10

debug10

cms10

c-language10

simulator10

llvm10

simulations10

offline-web-app10

c1110

interpreter10

offline-app10

Programming languages (22)

JavaC++CRustRPCCMakeTeXMakefile

Github contributions (5)

root-project/cling

Apr 2022 - Jan 2023

The cling C++ interpreter

Role in this project:

Backend Developer

Contributions:24 commits, 3 PRs, 25 comments in 9 months

Contributions summary:Jonas primarily contributed to the Cling C++ interpreter by addressing compiler warnings, improving code stability, and optimizing performance. Their work involved modifying existing code to use logical operators, handling potential crashes related to file operations, and reverting a profiling/debugging feature for compatibility. They also made changes to the code generation process, including fixing issues related to vtable emission and template argument printing.

cppclangc-plus-plusjupytercling

root-project/root

Nov 2020 - Jan 2023

The official repository for ROOT: analyzing, storing and visualizing big data, scientifically

Role in this project:

Back-end Developer & Performance Engineer

Contributions:890 reviews, 197 commits, 832 PRs in 2 years 2 months

Contributions summary:Jonas implemented and optimized the RANLUX++ random number generator within the ROOT framework. They focused on improving the efficiency of the modular multiplication algorithm through various optimizations, including using __int128, unrolling loops, optimizing carry propagation, and handling overflow. Furthermore, they refactored the core components of the generator and made changes for handling multi-dimensional arrays which improved overall performance.

pythonroot-cernmathematicsc-plus-plusscientific-visualization

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