solvecraft/solidcore/harness/mathprobe

mathprobe: does f64::sin give the same bits everywhere?

difftest proves solidcore matches the C++ bit for bit on Linux x86_64 with glibc. There, Rust's f64::sin and the C++ sin both call glibc's sin, and so does every other measured function except cbrt. compiler_builtins defines its own cbrt, and a pure-Rust Linux binary binds to it unless libm is linked earlier. On other targets, Rust uses a different libm: Apple's on macOS, and on wasm32-unknown-unknown the pure-Rust libm in compiler_builtins. This probe measures how often those differ.

For each std f64 method solidcore calls (sin, cos, tan, asin, acos, atan, atan2, sinh, cosh, ln, log10, cbrt, powf, powi; sqrt is correctly rounded everywhere, so it is left out), gen.py writes 200,000 deterministic inputs. They are weighted toward what a geometry kernel passes: angles within a few turns, values near multiples of π/2, near-±1 arguments for acos/asin, and wide log-uniform ranges. The probe then evaluates them

• on the host, as a Rust binary (src/bin/native.rs);
• as a wasm32-unknown-unknown module run by node (wasmeval.mjs); node passes f64 values through bit for bit, and the math runs inside the module;
• with docker, through Python's math module (a thin wrapper over the C libm) in ubuntu:24.04 on linux/amd64 and linux/arm64. That is glibc 2.39, the same base image as CI's hosted runners;

and compare.py reports, per function, how many results differ from glibc x86_64 in any bit, and by how many ulp at most. It also compares the host's Rust binary with Python on the same host (the host's C libm). A nonzero row there means Rust does not call the platform libm for that function, like cbrt in a pure-Rust Linux binary.

harness/mathprobe/run.sh          # work files in bin/mathprobe/

It needs Python 3.11+, node, a Rust toolchain with the wasm32-unknown-unknown target (set CARGO=/RUSTC= if the cargo on PATH is not rustup's) and, for the glibc columns, docker. Under emulation linux/amd64 must report fma (printed before its row), or glibc takes different code paths than on CI's hardware.

The results, and what they mean for difftest and wasm, are in plan/findings.md (General, "Math libraries differ by platform").