You can see all the details at: https://github.com/mratsim/constantine , but to answer your "how" question briefly here, something Nim shares with most (all?) "systems programming languages" is "easy" integration with assembly languages -- whatever the backend for "most" compiled code is (whatever that "most" even is - weighted by any number of measures of static source size or dynamic instruction counts). Of course, hand-rolled assembly can cost you a lot in portability/effort to port to new platforms/etc.
The entire concept of the "performance of a PLang" in terms of the run-time of programs written "mostly in it" is rather seriously under-specified, TBH. This is (or should be) uncontentious in spite of the slew of articles with titles like the one for this thread.
Exactly, Constantine generates assembly output and links that into normal Nim objects (e.g. C). That can then used in Nim or in Rust, Go, etc.
From its "Why Nim" in the readme:
- Assembly support either inline or a simple {.compile: "myasm.S".} away
- No GC if no GC-ed types are used (automatic memory management is set at the type level and optimized for latency/soft-realtime by default and can be totally deactivated).
- Procedural macros working directly on AST to create generic curve configuration, derive constants write a size-independent inline assembly code generator
The entire concept of the "performance of a PLang" in terms of the run-time of programs written "mostly in it" is rather seriously under-specified, TBH. This is (or should be) uncontentious in spite of the slew of articles with titles like the one for this thread.