GNU C Library Lands X86_64 FMA'ed Cosh For A ~35% Improvement

Key Takeaways

• FMA-optimized cosh yields ~35% faster execution.
• Patch targets x86_64‑v3 (Intel/AMD) micro‑architecture.
• Included in glibc 2.44 release planned for August.
• Other core‑math functions (tanh, sinh) also receive updates.
• Older CPUs may experience mixed performance or regressions.

Summary

The GNU C Library (glibc) now includes an FMA‑optimized implementation of the hyperbolic cosine function, cosh(), delivering roughly a 35% speed boost on x86_64‑v3 Intel and AMD CPUs. The change was merged by Linaro engineer Adhemerval Zanella alongside other core‑math patches affecting tanh and sinh. This optimization lands in the upcoming glibc 2.44 release scheduled for August, marking the first major performance gain for glibc in some time. The update leverages modern ISA features while older CPUs see mixed effects.

Pulse Analysis

The GNU C Library remains a cornerstone of Linux software stacks, providing the standard implementation of mathematical functions used by countless applications. By introducing a fused‑multiply‑add (FMA) version of cosh(), glibc taps into the higher‑throughput arithmetic pathways present in recent x86_64 processors. FMA reduces instruction count and rounding errors, translating directly into lower latency for the hyperbolic cosine calculation—a function frequently called in scientific simulations, signal processing, and machine‑learning kernels.

Benchmark data released by Phoronix shows the new cosh() implementation delivering roughly a 35% performance uplift when compiled for the x86_64‑v3 feature set. This gain is most pronounced on CPUs that fully support AVX2, FMA3, and related extensions, allowing the library to replace the older SSE2‑based routine. While the improvement is substantial for modern hardware, the patch suite also includes adjustments to tanh and sinh that yield mixed results on legacy architectures, underscoring the careful balance developers must strike between forward‑looking optimizations and backward compatibility.

Looking ahead, the optimization is slated for inclusion in glibc 2.44, expected in August. Its arrival demonstrates the library’s proactive approach to extracting performance from evolving processor designs, a trend that benefits high‑performance computing, cloud services, and embedded systems alike. As more applications rely on glibc’s math routines, such low‑level enhancements can cascade into noticeable end‑user speedups, reinforcing the importance of continuous collaboration between open‑source maintainers and hardware vendors.