Files
trueskill-tt/Cargo.toml
T
logaritmiskandClaude Opus 5 3dd659307a fix: replace the erfc approximation with libm, for free
#41 asked whether the Numerical Recipes `erfcc` approximation — 1.2e-7
relative, and the binding accuracy constraint on the whole crate — was
worth replacing, given it sits in the inference hot loop. It is, and it
costs nothing.

Measured, against an independent incomplete-gamma reference:

    range        previous (NR)        libm
    [-3, 0]            7.95e-8     2.15e-14
    [0, 0.5]           8.69e-8     4.70e-14
    [0.5, 2]           9.38e-8     1.24e-12
    [2, 6]             1.04e-7     5.20e-14
    [6, 26]            1.07e-7     1.75e-13

    erfc(0)          1.00000003          1.0  (exactly)
    |erfc(z)+erfc(-z)-2|  6.00e-8     2.22e-16

Performance, on `benches/batch.rs`: change [-3.34% +2.26%], p = 0.89 —
no change detected.

That result is counterintuitive, because libm's erfc is 1.65x slower
when swept uniformly over [-2.5, 2.5]. The sweep was the wrong input
distribution. Capturing the arguments inference actually passes:

    |x|<0.5    96.16%
    0.5-0.84    2.05%
    0.84-1.25   1.24%
    1.25-2      0.54%
    2-6         0.00%

98% fall below 0.84375, which is exactly where FDLIBM skips the
exponential entirely — while the NR form always pays for one. On the
real trace libm is the faster of the two (3.23 vs 3.78 ns/call).

An ad-hoc `Instant` harness reported a 16% end-to-end speedup; that was
an artifact of its own setup allocating and leaking per run, and
criterion's verdict of "no change" is the one to believe.

What it bought:

- `compute_margin` against exact quantiles: 8.4e-8 -> 1.7e-16.
- `cdf(mu, mu, sigma)` is now exactly 0.5; it was 1.5e-8 out.
- `sf + cdf` sums to one within a ULP, from 3e-8.
- `erfcx`'s two branches now agree to round-off across the crossover
  rather than to 1e-7, so the log-space evidence path and the linear one
  are consistent.
- Ten test tolerances tightened from 1e-6 to 1e-13..1e-15, and the
  prediction floor is now the integrator's rather than `cdf`'s.

Five goldens moved, by 2.4e-9 to 6e-7 — the magnitude of the removed
error, and `test_env_ttt`'s mu still rounds to the same six decimals.
Re-recorded with more digits so future drift stays visible. Verified as
movement toward truth per the goldens policy: every value now derives
from a primitive checked against an independent reference and satisfying
the exact identities, which the previous one did not.

Adds `libm` — zero transitive dependencies, rust-lang maintained.

Closes #41

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011hcFjNDmHXZF8URGLku5zZ
2026-09-07 22:25:00 +02:00

82 lines
2.1 KiB
TOML

[package]
name = "trueskill-tt"
version = "0.4.1"
edition = "2024"
rust-version = "1.85"
description = "TrueSkill Through Time: Bayesian skill rating that tracks how skill evolves over time, via Gaussian message passing"
repository = "https://git.aceofba.se/logaritmisk/trueskill-tt"
authors = ["Anders Olsson"]
# Publishing is restricted to the private kellnr registry; this also makes
# an accidental `cargo publish` to crates.io a hard error rather than a
# irreversible mistake. Index is declared in `.cargo/config.toml`.
publish = ["kellnr"]
readme = "README.md"
keywords = ["trueskill", "rating", "bayesian", "elo", "skill"]
categories = ["algorithms", "science", "game-development"]
license = "MIT OR Apache-2.0"
# `examples/atp.csv` is a 48 MB tennis dataset — 99% of the packaged crate,
# for a library whose source is 312 KB. `examples/atp.rs` opens it by
# relative path at runtime, so excluding the data still compiles; the
# example just needs the file fetched from the repo to run.
exclude = [
"/docs",
"/benches/*.txt",
"/temp",
"/.gitea",
"/examples/atp.csv",
]
[lib]
bench = false
[[bench]]
name = "batch"
harness = false
[[bench]]
name = "gaussian"
harness = false
[[bench]]
name = "history_converge"
harness = false
[[bench]]
name = "scored"
harness = false
[[bench]]
name = "ingest"
harness = false
[dependencies]
approx = { version = "0.5.1", optional = true }
libm = "0.2.16"
rayon = { version = "1", optional = true }
smallvec = "1"
[features]
approx = ["dep:approx"]
rayon = ["dep:rayon"]
[dev-dependencies]
criterion = "0.5"
plotters = { version = "0.3", default-features = false, features = ["svg_backend", "all_elements", "all_series"] }
plotters-backend = "0.3"
proptest = "1.11.0"
time = { version = "0.3", features = ["parsing"] }
trueskill-tt = { path = ".", features = ["approx"] }
# Debug symbols in release are for `just flame` (cargo-flamegraph), which needs
# them to symbolicate. Profile settings in a library are ignored by downstream
# consumers, so these only affect local builds — this is deliberate, not an
# oversight.
[profile.release]
debug = true
[profile.bench]
debug = true
[profile.dev]
debug = true