This repository provides two core Rust libraries: `compiler-builtins` and `libm`. `compiler-builtins` is a pure-Rust port of LLVM's `compiler-rt` intrinsics, including integer arithmetic (division, multiplication, leading/trailing zeros), floating-point operations (add, sub, mul, div, pow, conversion, truncation, extension), memory operations (memcpy, memset, memcmp), and platform-specific atomics. It is used by the Rust compiler to link against required runtime symbols for bare-metal and embedded targets. `libm` is a pure-Rust implementation of the C standard math library, ported from musl, covering trigonometric, exponential, logarithmic, power, Bessel, error, gamma, and rounding functions for f32 and f64, with experimental f16/f128 support. Both crates are `#![no_std]` and rely only on `core`. The codebase exhibits strong engineering: extensive use of generic traits (Float, Int) to abstract over widths, macro-driven code generation (intrinsics!, division algorithm macros, benchmark macros), architecture-specific optimizations (x86 SSE/AVX, ARM NEON, AArch64 outline atomics, Wasm, LoongArch, Hexagon assembly), and rigorous correctness verification against MPFR (via rug) and musl. CI tests run across 20+ targets, including instruction-count and wall-time benchmarks. This code is foundational for the Rust ecosystem, particularly in embedded, WebAssembly, and systems programming.